I will piece together the pages from the manual Language Refence:

http://127.0.0.1/php/php.net-ref/manual/langref.html


Language Reference

    * Basic syntax
          o Escaping from HTML
          o Instruction separation
          o Comments
    * Types
          o Introduction
          o Booleans
          o Integers
          o Floating point numbers
          o Strings
          o Arrays
          o Objects
          o Resources
          o NULL
          o Pseudo-types and variables used in this documentation
          o Type Juggling
    * Variables
          o Basics
          o Predefined Variables
          o Variable scope
          o Variable variables
          o Variables From External Sources
    * Constants
          o Syntax
          o Magic constants
    * Expressions
    * Operators
          o Operator Precedence
          o Arithmetic Operators
          o Assignment Operators
          o Bitwise Operators
          o Comparison Operators
          o Error Control Operators
          o Execution Operators
          o Incrementing/Decrementing Operators
          o Logical Operators
          o String Operators
          o Array Operators
          o Type Operators
    * Control Structures
          o Introduction
          o if
          o else
          o elseif/else if
          o Alternative syntax for control structures
          o while
          o do-while
          o for
          o foreach
          o break
          o continue
          o switch
          o declare
          o return
          o require
          o include
          o require_once
          o include_once
          o goto
    * Functions
          o User-defined functions
          o Function arguments
          o Returning values
          o Variable functions
          o Internal (built-in) functions
          o Anonymous functions
    * Classes and Objects
          o Introduction
          o The Basics
          o Properties
          o Class Constants
          o Autoloading Classes
          o Constructors and Destructors
          o Visibility
          o Object Inheritance
          o Scope Resolution Operator (::)
          o Static Keyword
          o Class Abstraction
          o Object Interfaces
          o Overloading
          o Object Iteration
          o Patterns
          o Magic Methods
          o Final Keyword
          o Object Cloning
          o Comparing Objects
          o Type Hinting
          o Late Static Bindings
          o Objects and references
          o Object Serialization
          o OOP Changelog
    * Namespaces
          o Namespaces overview
          o Defining namespaces
          o Declaring sub-namespaces
          o Defining multiple namespaces in the same file
          o Using namespaces: Basics
          o Namespaces and dynamic language features
          o namespace keyword and __NAMESPACE__ constant
          o Using namespaces: Aliasing/Importing
          o Global space
          o Using namespaces: fallback to global function/constant
          o Name resolution rules
          o FAQ: things you need to know about namespaces
    * Exceptions
          o Extending Exceptions
    * References Explained
          o What References Are
          o What References Do
          o What References Are Not
          o Passing by Reference
          o Returning References
          o Unsetting References
          o Spotting References
    * Predefined Variables
          o Superglobals — Superglobals are built-in variables that are always available in all scopes
          o $GLOBALS — References all variables available in global scope
          o $_SERVER — Server and execution environment information
          o $_GET — HTTP GET variables
          o $_POST — HTTP POST variables
          o $_FILES — HTTP File Upload variables
          o $_REQUEST — HTTP Request variables
          o $_SESSION — Session variables
          o $_ENV — Environment variables
          o $_COOKIE — HTTP Cookies
          o $php_errormsg — The previous error message
          o $HTTP_RAW_POST_DATA — Raw POST data
          o $http_response_header — HTTP response headers
          o $argc — The number of arguments passed to script
          o $argv — Array of arguments passed to script
    * Predefined Exceptions
          o Exception
          o ErrorException
    * Predefined Interfaces
          o Traversable — The Traversable interface
          o Iterator — The Iterator interface
          o IteratorAggregate — The IteratorAggregate interface
          o ArrayAccess — The ArrayAccess interface
          o Serializable — The Serializable interface
    * Context options and parameters
          o Socket context options — Socket context option listing
          o HTTP context options — HTTP context option listing
          o FTP context options — FTP context option listing
          o SSL context options — SSL context option listing
          o CURL context options — CURL context option listing
          o Phar context options — Phar context option listing
          o Context parameters — Context parameter listing
    * Supported Protocols and Wrappers
          o file:// — Accessing local filesystem
          o http:// — Accessing HTTP(s) URLs
          o ftp:// — Accessing FTP(s) URLs
          o php:// — Accessing various I/O streams
          o zlib:// — Compression Streams
          o data:// — Data (RFC 2397)
          o glob:// — Find pathnames matching pattern
          o phar:// — PHP Archive
          o ssh2:// — Secure Shell 2
          o rar:// — RAR
          o ogg:// — Audio streams
          o expect:// — Process Interaction Streams

=====================================================================
=====================================================================
    * Basic syntax
=====================================================================

Escaping from HTML

When PHP parses a file, it looks for opening and closing tags, which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows PHP to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser. Most of the time you will see PHP embedded in HTML documents, as in this example.
<p>This is going to be ignored.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored.</p>

You can also use more advanced structures:

Example #1 Advanced escaping
<?php
if ($expression) {
    ?>
    <strong>This is true.</strong>
    <?php
} else {
    ?>
    <strong>This is false.</strong>
    <?php
}
?>
This works as expected, because when PHP hits the ?> closing tags, it simply starts outputting whatever it finds (except for an immediately following newline - see instruction separation ) until it hits another opening tag. The example given here is contrived, of course, but for outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo() or print().

There are four different pairs of opening and closing tags which can be used in PHP. Two of those, <?php ?> and <script language="php"> </script>, are always available. The other two are short tags and ASP style tags, and can be turned on and off from the php.ini configuration file. As such, while some people find short tags and ASP style tags convenient, they are less portable, and generally not recommended.

Note:
  Also note that if you are embedding PHP within XML or XHTML you will need to use the <?php ?> tags to remain compliant with standards.

Example #2 PHP Opening and Closing Tags
1.  <?php echo 'if you want to serve XHTML or XML documents, do it like this'; ?>

2.  <script language="php">
        echo 'some editors (like FrontPage) don\'t
              like processing instructions';
    </script>

3.  <? echo 'this is the simplest, an SGML processing instruction'; ?>
    <?= expression ?> This is a shortcut for "<? echo expression ?>"

4.  <% echo 'You may optionally use ASP-style tags'; %>
    <%= $variable; # This is a shortcut for "<% echo . . ." %>

While the tags seen in examples one and two are both always available, example one is the most commonly used, and recommended, of the two.

Short tags (example three) are only available when they are enabled via the short_open_tag php.ini configuration file directive, or if PHP was configured with the --enable-short-tags option.

ASP style tags (example four) are only available when they are enabled via the asp_tags php.ini configuration file directive.

Note:
  Using short tags should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.

Note:
  In PHP 5.2 and earlier, the parser does not allow the <?php opening tag to be the only thing in a file. This is allowed as of PHP 5.3.

=====================================================================


Instruction separation

As in C or Perl, PHP requires instructions to be terminated with a semicolon at the end of each statement. The closing tag of a block of PHP code automatically implies a semicolon; you do not need to have a semicolon terminating the last line of a PHP block. The closing tag for the block will include the immediately trailing newline if one is present.
<?php
    echo 'This is a test';
?>

<?php echo 'This is a test' ?>

<?php echo 'We omitted the last closing tag';

    Note:

    The closing tag of a PHP block at the end of a file is optional, and in some cases omitting it is helpful when using include() or require(), so unwanted whitespace will not occur at the end of files, and you will still be able to add headers to the response later. It is also handy if you use output buffering, and would not like to see added unwanted whitespace at the end of the parts generated by the included files.

=====================================================================


Comments

PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:
<?php
    echo 'This is a test'; // This is a one-line c++ style comment
    /* This is a multi line comment
       yet another line of comment */
    echo 'This is yet another test';
    echo 'One Final Test'; # This is a one-line shell-style comment
?>

The "one-line" comment styles only comment to the end of the line or the current block of PHP code, whichever comes first. This means that HTML code after // ... ?> or # ... ?> WILL be printed: ?> breaks out of PHP mode and returns to HTML mode, and // or # cannot influence that. If the asp_tags configuration directive is enabled, it behaves the same with // %> and # %>. However, the </script> tag doesn't break out of PHP mode in a one-line comment.

<h1>This is an <?php # echo 'simple';?> example</h1>
<p>The header above will say 'This is an  example'.</p>

'C' style comments end at the first */ encountered. Make sure you don't nest 'C' style comments. It is easy to make this mistake if you are trying to comment out a large block of code.

<?php
 /*
    echo 'This is a test'; /* This comment will cause a problem */
 */
?>

=====================================================================
=====================================================================
    * Types
=====================================================================


Introduction

PHP supports eight primitive types.

Four scalar types:

    * boolean
    * integer
    * float (floating-point number, aka double)
    * string

Two compound types:

    * array
    * object

And finally two special types:

    * resource
    * NULL

This manual also introduces some pseudo-types for readability reasons:

    * mixed
    * number
    * callback

And the pseudo-variable $....

Some references to the type "double" may remain in the manual. Consider double the same as float; the two names exist only for historic reasons.

The type of a variable is not usually set by the programmer; rather, it is decided at runtime by PHP depending on the context in which that variable is used.

    Note: To check the type and value of an expression, use the var_dump() function.

    To get a human-readable representation of a type for debugging, use the gettype() function. To check for a certain type, do not use gettype(), but rather the is_type functions. Some examples:
    <?php
    $a_bool = TRUE;   // a boolean
    $a_str  = "foo";  // a string
    $a_str2 = 'foo';  // a string
    $an_int = 12;     // an integer

    echo gettype($a_bool); // prints out:  boolean
    echo gettype($a_str);  // prints out:  string

    // If this is an integer, increment it by four
    if (is_int($an_int)) {
        $an_int += 4;
    }

    // If $a_bool is a string, print it out
    // (does not print out anything)
    if (is_string($a_bool)) {
        echo "String: $a_bool";
    }
    ?>

To forcibly convert a variable to a certain type, either cast the variable or use the settype() function on it.

Note that a variable may be evaluated with different values in certain situations, depending on what type it is at the time. For more information, see the section on Type Juggling. The type comparison tables may also be useful, as they show examples of various type-related comparisons.

=====================================================================


Booleans

This is the simplest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

    Note: The boolean type was introduced in PHP 4. 

Syntax

To specify a boolean literal, use the keywords TRUE or FALSE. Both are case-insensitive.
<?php
$foo = True; // assign the value TRUE to $foo
?>

Typically, the result of an operator which returns a boolean value is passed on to a control structure.
<?php
// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
    echo "The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...because this can be used with exactly the same meaning:
if ($show_separators) {
    echo "<hr>\n";
}
?>
Converting to boolean

To explicitly convert a value to boolean, use the (bool) or (boolean) casts. However, in most cases the cast is unnecessary, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

See also Type Juggling.

When converting to boolean, the following values are considered FALSE:

    * the boolean FALSE itself
    * the integer 0 (zero)
    * the float 0.0 (zero)
    * the empty string, and the string "0"
    * an array with zero elements
    * an object with zero member variables (PHP 4 only)
    * the special type NULL (including unset variables)
    * SimpleXML objects created from empty tags

Every other value is considered TRUE (including any resource).
Warning

-1 is considered TRUE, like any other non-zero (whether negative or positive) number!
<?php
var_dump((bool) "");        // bool(false)
var_dump((bool) 1);         // bool(true)
var_dump((bool) -2);        // bool(true)
var_dump((bool) "foo");     // bool(true)
var_dump((bool) 2.3e5);     // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array());   // bool(false)
var_dump((bool) "false");   // bool(true)
?>

=====================================================================


Integers

An integer is a number of the set ℤ = {..., -2, -1, 0, 1, 2, ...}.

See also:

    * Arbitrary length integer / GMP
    * Floating point numbers
    * Arbitrary precision / BCMath

Syntax

Integers can be specified in decimal (base 10), hexadecimal (base 16), or octal (base 8) notation, optionally preceded by a sign (- or +).

To use octal notation, precede the number with a 0 (zero). To use hexadecimal notation precede the number with 0x.

Example #1 Integer literals
<?php
$a = 1234; // decimal number
$a = -123; // a negative number
$a = 0123; // octal number (equivalent to 83 decimal)
$a = 0x1A; // hexadecimal number (equivalent to 26 decimal)
?>

Formally, the structure for integer literals is:

decimal     : [1-9][0-9]*
            | 0

hexadecimal : 0[xX][0-9a-fA-F]+

octal       : 0[0-7]+

integer     : [+-]?decimal
            | [+-]?hexadecimal
            | [+-]?octal

The size of an integer is platform-dependent, although a maximum value of about two billion is the usual value (that's 32 bits signed). 64-bit platforms usually have a maximum value of about 9E18. PHP does not support unsigned integers. Integer size can be determined using the constant PHP_INT_SIZE, and maximum value using the constant PHP_INT_MAX since PHP 4.4.0 and PHP 5.0.5.

Warning
If an invalid digit is given in an octal integer (i.e. 8 or 9), the rest of the number is ignored.

Example #2 Octal weirdness

<?php
var_dump(01090); // 010 octal = 8 decimal
?>

----------------
Integer overflow

If PHP encounters a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, an operation which results in a number beyond the bounds of the integer type will return a float instead.

Example #3 Integer overflow on a 32-bit system
<?php
$large_number = 2147483647;
var_dump($large_number);                     // int(2147483647)

$large_number = 2147483648;
var_dump($large_number);                     // float(2147483648)

$million = 1000000;
$large_number =  50000 * $million;
var_dump($large_number);                     // float(50000000000)
?>

Example #4 Integer overflow on a 64-bit system
<?php
$large_number = 9223372036854775807;
var_dump($large_number);                     // int(9223372036854775807)

$large_number = 9223372036854775808;
var_dump($large_number);                     // float(9.2233720368548E+18)

$million = 1000000;
$large_number =  50000000000000 * $million;
var_dump($large_number);                     // float(5.0E+19)
?>

There is no integer division operator in PHP. 1/2 yields the float 0.5. The value can be casted to an integer to round it downwards, or the round() function provides finer control over rounding.
<?php
var_dump(25/7);         // float(3.5714285714286) 
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7));  // float(4) 
?>
Converting to integer

To explicitly convert a value to integer, use either the (int) or (integer) casts. However, in most cases the cast is not needed, since a value will be automatically converted if an operator, function or control structure requires an integer argument. A value can also be converted to integer with the intval() function.

See also: type-juggling.
From booleans

FALSE will yield 0 (zero), and TRUE will yield 1 (one).
From floating point numbers

When converting from float to integer, the number will be rounded towards zero.

If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms), the result is undefined, since the float doesn't have enough precision to give an exact integer result. No warning, not even a notice will be issued when this happens!
Warning

Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.
<?php
echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
?>

See also the warning about float precision.
From strings

See String conversion to numbers
From other types

Caution
  The behaviour of converting to integer is undefined for other types. Do not rely on any observed behaviour, as it can change without notice.

=====================================================================


Floating point numbers

Floating point numbers (also known as "floats", "doubles", or "real numbers") can be specified using any of the following syntaxes:
<?php
$a = 1.234; 
$b = 1.2e3; 
$c = 7E-10;
?>

Formally:

LNUM          [0-9]+
DNUM          ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM [+-]?(({LNUM} | {DNUM}) [eE][+-]? {LNUM})

The size of a float is platform-dependent, although a maximum of ~1.8e308 with a precision of roughly 14 decimal digits is a common value (the 64 bit IEEE format).
Warning
Floating point precision

Floating point numbers have limited precision. Although it depends on the system, PHP typically uses the IEEE 754 double precision format, which will give a maximum relative error due to rounding in the order of 1.11e-16. Non elementary arithmetic operations may give larger errors, and, of course, error progragation must be considered when several operations are compounded.

Additionally, rational numbers that are exactly representable as floating point numbers in base 10, like 0.1 or 0.7, do not have an exact representation as floating point numbers in base 2, which is used internally, no matter the size of the mantissa. Hence, they cannot be converted into their internal binary counterparts without a small loss of precision. This can lead to confusing results: for example, floor((0.1+0.7)*10) will usually return 7 instead of the expected 8, since the internal representation will be something like 7.9999999999999991118....

So never trust floating number results to the last digit, and never compare floating point numbers for equality. If higher precision is necessary, the arbitrary precision math functions and gmp functions are available.
Converting to float

For information on converting strings to float, see String conversion to numbers. For values of other types, the conversion is performed by converting the value to integer first and then to float. See Converting to integer for more information. As of PHP 5, a notice is thrown if an object is converted to float.

=====================================================================


Strings

A string is series of characters, where a character is the same as a byte. This means that PHP only supports a 256-character set, and hence does not offer native Unicode support. See utf8_encode() and utf8_decode() for some basic Unicode functionality.

    Note: It is no problem for a string to become very large. PHP imposes no boundary on the size of a string; the only limit is the available memory of the computer on which PHP is running. 

Syntax

A string literal can be specified in four different ways:

    * single quoted
    * double quoted
    * heredoc syntax
    * nowdoc syntax (since PHP 5.3.0)

Single quoted

The simplest way to specify a string is to enclose it in single quotes (the character ').

To specify a literal single quote, escape it with a backslash (\). To specify a literal backslash, double it (\\). All other instances of backslash will be treated as a literal backslash: this means that the other escape sequences you might be used to, such as \r or \n, will be output literally as specified rather than having any special meaning.

    Note: Unlike the double-quoted and heredoc syntaxes, variables and escape sequences for special characters will not be expanded when they occur in single quoted strings. 

<?php
echo 'this is a simple string';

echo 'You can also have embedded newlines in 
strings this way as it is
okay to do';

// Outputs: Arnold once said: "I'll be back"
echo 'Arnold once said: "I\'ll be back"';

// Outputs: You deleted C:\*.*?
echo 'You deleted C:\\*.*?';

// Outputs: You deleted C:\*.*?
echo 'You deleted C:\*.*?';

// Outputs: This will not expand: \n a newline
echo 'This will not expand: \n a newline';

// Outputs: Variables do not $expand $either
echo 'Variables do not $expand $either';
?>
Double quoted

If the string is enclosed in double-quotes ("), PHP will interpret more escape sequences for special characters:
Escaped characters Sequence 	Meaning
\n 	linefeed (LF or 0x0A (10) in ASCII)
\r 	carriage return (CR or 0x0D (13) in ASCII)
\t 	horizontal tab (HT or 0x09 (9) in ASCII)
\v 	vertical tab (VT or 0x0B (11) in ASCII) (since PHP 5.2.5)
\f 	form feed (FF or 0x0C (12) in ASCII) (since PHP 5.2.5)
\\ 	backslash
\$ 	dollar sign
\" 	double-quote
\[0-7]{1,3} 	the sequence of characters matching the regular expression is a character in octal notation
\x[0-9A-Fa-f]{1,2} 	the sequence of characters matching the regular expression is a character in hexadecimal notation

As in single quoted strings, escaping any other character will result in the backslash being printed too. Before PHP 5.1.1, the backslash in \{$var} had not been printed.

The most important feature of double-quoted strings is the fact that variable names will be expanded. See string parsing for details.
Heredoc

A third way to delimit strings is the heredoc syntax: <<<. After this operator, an identifier is provided, then a newline. The string itself follows, and then the same identifier again to close the quotation.

The closing identifier must begin in the first column of the line. Also, the identifier must follow the same naming rules as any other label in PHP: it must contain only alphanumeric characters and underscores, and must start with a non-digit character or underscore.
Warning

It is very important to note that the line with the closing identifier must contain no other characters, except possibly a semicolon (;). That means especially that the identifier may not be indented, and there may not be any spaces or tabs before or after the semicolon. It's also important to realize that the first character before the closing identifier must be a newline as defined by the local operating system. This is \n on UNIX systems, including Mac OS X. The closing delimiter (possibly followed by a semicolon) must also be followed by a newline.

If this rule is broken and the closing identifier is not "clean", it will not be considered a closing identifier, and PHP will continue looking for one. If a proper closing identifier is not found before the end of the current file, a parse error will result at the last line.

Heredocs can not be used for initializing class properties. Since PHP 5.3, this limitation is valid only for heredocs containing variables.

Example #1 Invalid example
<?php
class foo {
    public $bar = <<<EOT
bar
    EOT;
}
?>

Heredoc text behaves just like a double-quoted string, without the double quotes. This means that quotes in a heredoc do not need to be escaped, but the escape codes listed above can still be used. Variables are expanded, but the same care must be taken when expressing complex variables inside a heredoc as with strings.

Example #2 Heredoc string quoting example
<?php
$str = <<<EOD
Example of string
spanning multiple lines
using heredoc syntax.
EOD;

/* More complex example, with variables. */
class foo
{
    var $foo;
    var $bar;

    function foo()
    {
        $this->foo = 'Foo';
        $this->bar = array('Bar1', 'Bar2', 'Bar3');
    }
}

$foo = new foo();
$name = 'MyName';

echo <<<EOT
My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should print a capital 'A': \x41
EOT;
?>

The above example will output:

My name is "MyName". I am printing some Foo.
Now, I am printing some Bar2.
This should print a capital 'A': A

It is also possible to use the Heredoc syntax to pass data to function arguments:

Example #3 Heredoc in arguments example
<?php
var_dump(array(<<<EOD
foobar!
EOD
));
?>

As of PHP 5.3.0, it's possible to initialize static variables and class properties/constants using the Heredoc syntax:

Example #4 Using Heredoc to initialize static values
<?php
// Static variables
function foo()
{
    static $bar = <<<LABEL
Nothing in here...
LABEL;
}

// Class properties/constants
class foo
{
    const BAR = <<<FOOBAR
Constant example
FOOBAR;

    public $baz = <<<FOOBAR
Property example
FOOBAR;
}
?>

Starting with PHP 5.3.0, the opening Heredoc identifier may optionally be enclosed in double quotes:

Example #5 Using double quotes in Heredoc
<?php
echo <<<"FOOBAR"
Hello World!
FOOBAR;
?>

    Note:

    Heredoc support was added in PHP 4.

Nowdoc

Nowdocs are to single-quoted strings what heredocs are to double-quoted strings. A nowdoc is specified similarly to a heredoc, but no parsing is done inside a nowdoc. The construct is ideal for embedding PHP code or other large blocks of text without the need for escaping. It shares some features in common with the SGML <![CDATA[ ]]> construct, in that it declares a block of text which is not for parsing.

A nowdoc is identified with the same <<< sequence used for heredocs, but the identifier which follows is enclosed in single quotes, e.g. <<<'EOT'. All the rules for heredoc identifiers also apply to nowdoc identifiers, especially those regarding the appearance of the closing identifier.

Example #6 Nowdoc string quoting example
<?php
$str = <<<'EOD'
Example of string
spanning multiple lines
using nowdoc syntax.
EOD;

/* More complex example, with variables. */
class foo
{
    public $foo;
    public $bar;

    function foo()
    {
        $this->foo = 'Foo';
        $this->bar = array('Bar1', 'Bar2', 'Bar3');
    }
}

$foo = new foo();
$name = 'MyName';

echo <<<'EOT'
My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should not print a capital 'A': \x41
EOT;
?>

The above example will output:

My name is "$name". I am printing some $foo->foo.
Now, I am printing some {$foo->bar[1]}.
This should not print a capital 'A': \x41

    Note:

    Unlike heredocs, nowdocs can be used in any static data context. The typical example is initializing class properties or constants:

    Example #7 Static data example
    <?php
    class foo {
        public $bar = <<<'EOT'
    bar
    EOT;
    }
    ?>

    Note:

    Nowdoc support was added in PHP 5.3.0.

Variable parsing

When a string is specified in double quotes or with heredoc, variables are parsed within it.

There are two types of syntax: a simple one and a complex one. The simple syntax is the most common and convenient. It provides a way to embed a variable, an array value, or an object property in a string with a minimum of effort.

The complex syntax was introduced in PHP 4, and can be recognised by the curly braces surrounding the expression.
Simple syntax

If a dollar sign ($) is encountered, the parser will greedily take as many tokens as possible to form a valid variable name. Enclose the variable name in curly braces to explicitly specify the end of the name.
<?php
$juice = "apple";

echo "He drank some $juice juice.".PHP_EOL;
echo "He drank some juice made of $juices."; // Invalid. "s" is a valid character for a variable name, but the variable is $juice.
?>

The above example will output:

He drank some apple juice.
He drank some juice made of .

Similarly, an array index or an object property can be parsed. With array indices, the closing square bracket (]) marks the end of the index. The same rules apply to object properties as to simple variables.

Example #8 Simple syntax example
<?php
$juices = array("apple", "orange", "koolaid1" => "purple");

echo "He drank some $juices[0] juice.".PHP_EOL;
echo "He drank some $juices[1] juice.".PHP_EOL;
echo "He drank some juice made of $juice[0]s.".PHP_EOL; // Won't work
echo "He drank some $juices[koolaid1] juice.".PHP_EOL;

class people {
    public $john = "John Smith";
    public $jane = "Jane Smith";
    public $robert = "Robert Paulsen";
    
    public $smith = "Smith";
}

$people = new people();

echo "$people->john drank some $juices[0] juice.".PHP_EOL;
echo "$people->john then said hello to $people->jane.".PHP_EOL;
echo "$people->john's wife greeted $people->robert.".PHP_EOL;
echo "$people->robert greeted the two $people->smiths."; // Won't work
?>

The above example will output:

He drank some apple juice.
He drank some orange juice.
He drank some juice made of s.
He drank some purple juice.
John Smith drank some apple juice.
John Smith then said hello to Jane Smith.
John Smith's wife greeted Robert Paulsen.
Robert Paulsen greeted the two .

For anything more complex, you should use the complex syntax.
Complex (curly) syntax

This isn't called complex because the syntax is complex, but because it allows for the use of complex expressions.

Any scalar variable, array element or object property with a string representation can be included via this syntax. Simply write the expression the same way as it would appear outside the string, and then wrap it in { and }. Since { can not be escaped, this syntax will only be recognised when the $ immediately follows the {. Use {\$ to get a literal {$. Some examples to make it clear:
<?php
// Show all errors
error_reporting(E_ALL);

$great = 'fantastic';

// Won't work, outputs: This is { fantastic}
echo "This is { $great}";

// Works, outputs: This is fantastic
echo "This is {$great}";
echo "This is ${great}";

// Works
echo "This square is {$square->width}00 centimeters broad."; 


// Works, quoted keys only work using the curly brace syntax
echo "This works: {$arr['key']}";


// Works
echo "This works: {$arr[4][3]}";

// This is wrong for the same reason as $foo[bar] is wrong  outside a string.
// In other words, it will still work, but only because PHP first looks for a
// constant named foo; an error of level E_NOTICE (undefined constant) will be
// thrown.
echo "This is wrong: {$arr[foo][3]}"; 

// Works. When using multi-dimensional arrays, always use braces around arrays
// when inside of strings
echo "This works: {$arr['foo'][3]}";

// Works.
echo "This works: " . $arr['foo'][3];

echo "This works too: {$obj->values[3]->name}";

echo "This is the value of the var named $name: {${$name}}";

echo "This is the value of the var named by the return value of getName(): {${getName()}}";

echo "This is the value of the var named by the return value of \$object->getName(): {${$object->getName()}}";

// Won't work, outputs: This is the return value of getName(): {getName()}
echo "This is the return value of getName(): {getName()}";
?>

It is also possible to access class properties using variables within strings using this syntax.
<?php
class foo {
    var $bar = 'I am bar.';
}

$foo = new foo();
$bar = 'bar';
$baz = array('foo', 'bar', 'baz', 'quux');
echo "{$foo->$bar}\n";
echo "{$foo->$baz[1]}\n";
?>

The above example will output:

I am bar.
I am bar.

    Note:

    Functions, method calls, static class variables, and class constants inside {$} work since PHP 5. However, the value accessed will be interpreted as the name of a variable in the scope in which the string is defined. Using single curly braces ({}) will not work for accessing the return values of functions or methods or the values of class constants or static class variables.

<?php
// Show all errors.
error_reporting(E_ALL);

class beers {
    const softdrink = 'rootbeer';
    public static $ale = 'ipa';
}

$rootbeer = 'A & W';
$ipa = 'Alexander Keith\'s';

// This works; outputs: I'd like an A & W
echo "I'd like an {${beers::softdrink}}\n";

// This works too; outputs: I'd like an Alexander Keith's
echo "I'd like an {${beers::$ale}}\n";
?>
String access and modification by character

Characters within strings may be accessed and modified by specifying the zero-based offset of the desired character after the string using square array brackets, as in $str[42]. Think of a string as an array of characters for this purpose. The functions substr() and substr_replace() can be used when you want to extract or replace more than 1 character.

    Note: Strings may also be accessed using braces, as in $str{42}, for the same purpose. 

Warning

Writing to an out of range offset pads the string with spaces. Non-integer types are converted to integer. Illegal offset type emits E_NOTICE. Negative offset emits E_NOTICE in write but reads empty string. Only the first character of an assigned string is used. Assigning empty string assigns NULL byte.

Example #9 Some string examples
<?php
// Get the first character of a string
$str = 'This is a test.';
$first = $str[0];

// Get the third character of a string
$third = $str[2];

// Get the last character of a string.
$str = 'This is still a test.';
$last = $str[strlen($str)-1]; 

// Modify the last character of a string
$str = 'Look at the sea';
$str[strlen($str)-1] = 'e';

?>

    Note:

    Accessing variables of other types (not including arrays or objects implementing the appropriate interfaces) using [] or {} silently returns NULL.

Useful functions and operators

Strings may be concatenated using the '.' (dot) operator. Note that the '+' (addition) operator will not work for this. See String operators for more information.

There are a number of useful functions for string manipulation.

See the string functions section for general functions, and the regular expression functions or the Perl-compatible regular expression functions for advanced find & replace functionality.

There are also functions for URL strings, and functions to encrypt/decrypt strings (mcrypt and mhash).

Finally, see also the character type functions.
Converting to string

A value can be converted to a string using the (string) cast or the strval() function. String conversion is automatically done in the scope of an expression where a string is needed. This happens when using the echo() or print() functions, or when a variable is compared to a string. The sections on Types and Type Juggling will make the following clearer. See also the settype() function.

A boolean TRUE value is converted to the string "1". Boolean FALSE is converted to "" (the empty string). This allows conversion back and forth between boolean and string values.

An integer or float is converted to a string representing the number textually (including the exponent part for floats). Floating point numbers can be converted using exponential notation (4.1E+6).

    Note:

    The decimal point character is defined in the script's locale (category LC_NUMERIC). See the setlocale() function.

Arrays are always converted to the string "Array"; because of this, echo() and print() can not by themselves show the contents of an array. To view a single element, use a construction such as echo $arr['foo']. See below for tips on viewing the entire contents.

Objects in PHP 4 are always converted to the string "Object". To print the values of object properties for debugging reasons, read the paragraphs below. To get an object's class name, use the get_class() function. As of PHP 5, the __toString method is used when applicable.

Resources are always converted to strings with the structure "Resource id #1", where 1 is the unique number assigned to the resource by PHP at runtime. Do not rely upon this structure; it is subject to change. To get a resource's type, use the get_resource_type() function.

NULL is always converted to an empty string.

As stated above, directly converting an array, object, or resource to a string does not provide any useful information about the value beyond its type. See the functions print_r() and var_dump() for more effective means of inspecting the contents of these types.

Most PHP values can also be converted to strings for permanent storage. This method is called serialization, and is performed by the serialize() function. If the PHP engine was built with WDDX support, PHP values can also be serialized as well-formed XML text.
String conversion to numbers

When a string is evaluated in a numeric context, the resulting value and type are determined as follows.

If the string does not contain any of the characters '.', 'e', or 'E' and the numeric value fits into integer type limits (as defined by PHP_INT_MAX), the string will be evaluated as an integer. In all other cases it will be evaluated as a float.

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.
<?php
$foo = 1 + "10.5";                // $foo is float (11.5)
$foo = 1 + "-1.3e3";              // $foo is float (-1299)
$foo = 1 + "bob-1.3e3";           // $foo is integer (1)
$foo = 1 + "bob3";                // $foo is integer (1)
$foo = 1 + "10 Small Pigs";       // $foo is integer (11)
$foo = 4 + "10.2 Little Piggies"; // $foo is float (14.2)
$foo = "10.0 pigs " + 1;          // $foo is float (11)
$foo = "10.0 pigs " + 1.0;        // $foo is float (11)     
?>

For more information on this conversion, see the Unix manual page for strtod(3).

To test any of the examples in this section, cut and paste the examples and insert the following line to see what's going on:
<?php
echo "\$foo==$foo; type is " . gettype ($foo) . "<br />\n";
?>

Do not expect to get the code of one character by converting it to integer, as is done in C. Use the ord() and chr() functions to convert between ASCII codes and characters.

=====================================================================


Arrays

An array in PHP is actually an ordered map. A map is a type that associates values to keys. This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and probably more. As array values can be other arrays, trees and multidimensional arrays are also possible.

Explanation of those data structures is beyond the scope of this manual, but at least one example is provided for each of them. For more information, look towards the considerable literature that exists about this broad topic.
Syntax
Specifying with array()

An array can be created by the array() language construct. It takes as parameters any number of comma-separated key => value pairs.

array(  key =>  value
     , ...
     )
// key may only be an integer or string
// value may be any value of any type

<?php
$arr = array("foo" => "bar", 12 => true);

echo $arr["foo"]; // bar
echo $arr[12];    // 1
?>

A key may be either an integer or a string. If a key is the standard representation of an integer, it will be interpreted as such (i.e. "8" will be interpreted as 8, while "08" will be interpreted as "08"). Floats in key are truncated to integer. The indexed and associative array types are the same type in PHP, which can both contain integer and string indices.

A value can be any PHP type.

Note:
  Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an E_NOTICE-level error message will be issued, and the result will be NULL.

<?php
$arr = array("somearray" => array(6 => 5, 13 => 9, "a" => 42));

echo $arr["somearray"][6];    // 5
echo $arr["somearray"][13];   // 9
echo $arr["somearray"]["a"];  // 42
?>

If a key is not specified for a value, the maximum of the integer indices is taken and the new key will be that value plus 1. If a key that already has an assigned value is specified, that value will be overwritten.

<?php
// This array is the same as ...
array(5 => 43, 32, 56, "b" => 12);

// ...this array
array(5 => 43, 6 => 32, 7 => 56, "b" => 12);
?>

Warning
  Before PHP 4.3.0, appending to an array in which the current maximum key was negative would create a new key as described above. Since PHP 4.3.0, the new key will be 0.

Using TRUE as key will evaluate to integer 1 as a key. Using FALSE as key will evaluate to integer 0 as a key. Using NULL as a key will evaluate to the empty string. Using the empty string as a key will create (or overwrite) a key with the empty string and its value; it is not the same as using empty brackets.

Arrays and objects can not be used as keys. Doing so will result in a warning: Illegal offset type.

---------------------------------------------
Creating/modifying with square bracket syntax

An existing array can be modified by explicitly setting values in it.

This is done by assigning values to the array, specifying the key in brackets. The key can also be omitted, resulting in an empty pair of brackets ([]).

$arr[key] = value;
$arr[] = value;
// key may be an integer or string
// value may be any value of any type

If $arr doesn't exist yet, it will be created, so this is also an alternative way to create an array. 

To change a certain value, assign a new value to that element using its key. 

To remove a key/value pair, call the unset() function on it.

<?php
$arr = array(5 => 1, 12 => 2);

$arr[] = 56;    // This is the same as $arr[13] = 56;
                // at this point of the script

$arr["x"] = 42; // This adds a new element to
                // the array with key "x"
                
unset($arr[5]); // This removes the element from the array

unset($arr);    // This deletes the whole array
?>

Note:
  As mentioned above, if no key is specified, the maximum of the existing integer indices is taken, and the new key will be that maximum value plus 1. If no integer indices exist yet, the key will be 0 (zero).

  Note that the maximum integer key used for this need not currently exist in the array. It need only have existed in the array at some time since the last time the array was re-indexed. The following example illustrates:

<?php
  // Create a simple array.
  $array = array(1, 2, 3, 4, 5);
  print_r($array);

  // Now delete every item, but leave the array itself intact:
  foreach ($array as $i => $value) {
    unset($array[$i]);
  }
  print_r($array);

  // Append an item (note that the new key is 5, instead of 0).
  $array[] = 6;
  print_r($array);

  // Re-index:
  $array = array_values($array);
  $array[] = 7;
  print_r($array);
?>

The above example will output:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
)
Array
(
)
Array
(
    [5] => 6
)
Array
(
    [0] => 6
    [1] => 7
)

----------------
Useful functions

There are quite a few useful functions for working with arrays. See the array functions section.
http://127.0.0.1/php/php.net-ref/manual/book.array.html

Note:
  The unset() function allows removing keys from an array. Be aware that the array will not be reindexed. If a true "remove and shift" behavior is desired, the array can be reindexed using the array_values() function.

<?php
  $a = array(1 => 'one', 2 => 'two', 3 => 'three');
  unset($a[2]);
  /* will produce an array that would have been defined as
     $a = array(1 => 'one', 3 => 'three');
     and NOT
     $a = array(1 => 'one', 2 =>'three');
  */

  $b = array_values($a);
  // Now $b is array(0 => 'one', 1 =>'three')
?>

The foreach control structure exists specifically for arrays. It provides an easy way to traverse an array.

---------------------
Array do's and don'ts

Why is $foo[bar] wrong?

Always use quotes around a string literal array index. For example, $foo['bar'] is correct, while $foo[bar] is not. But why? It is common to encounter this kind of syntax in old scripts:

<?php
  $foo[bar] = 'enemy';
  echo $foo[bar];
  // etc
?>

This is wrong, but it works. The reason is that this code has an undefined constant (bar) rather than a string ('bar' - notice the quotes). PHP may in future define constants which, unfortunately for such code, have the same name. It works because PHP automatically converts a bare string (an unquoted string which does not correspond to any known symbol) into a string which contains the bare string. For instance, if there is no defined constant named bar, then PHP will substitute in the string 'bar' and use that.

Note: This does not mean to always quote the key. 
Do not quote keys which are constants or variables, as this will prevent PHP from interpreting them.

<?php
    error_reporting(E_ALL);
    ini_set('display_errors', true);
    ini_set('html_errors', false);

    // Simple array:
    $array = array(1, 2);
    $count = count($array);
    for ($i = 0; $i < $count; $i++) {
        echo "\nChecking $i: \n";
        echo "Bad: " . $array['$i'] . "\n";
        echo "Good: " . $array[$i] . "\n";
        echo "Bad: {$array['$i']}\n";
        echo "Good: {$array[$i]}\n";
    }
?>

    The above example will output:

    Checking 0: 
    Notice: Undefined index:  $i in /path/to/script.html on line 9
    Bad: 
    Good: 1
    Notice: Undefined index:  $i in /path/to/script.html on line 11
    Bad: 
    Good: 1

    Checking 1: 
    Notice: Undefined index:  $i in /path/to/script.html on line 9
    Bad: 
    Good: 2
    Notice: Undefined index:  $i in /path/to/script.html on line 11
    Bad: 
    Good: 2

More examples to demonstrate this behaviour:
<?php
  // Show all errors
  error_reporting(E_ALL);

  $arr = array('fruit' => 'apple', 'veggie' => 'carrot');

  // Correct
  print $arr['fruit'];  // apple
  print $arr['veggie']; // carrot

  // Incorrect.  This works but also throws a PHP error of level E_NOTICE 
  // because of an undefined constant named fruit
  // 
  // Notice: Use of undefined constant fruit - assumed 'fruit' in...
  print $arr[fruit];    // apple

  // This defines a constant to demonstrate what's going on.  The value 'veggie'
  // is assigned to a constant named fruit.
  define('fruit', 'veggie');

  // Notice the difference now
  print $arr['fruit'];  // apple
  print $arr[fruit];    // carrot

  // The following is okay, as it's inside a string. Constants are not 
  // looked for/ within strings, so no E_NOTICE occurs here
  print "Hello $arr[fruit]";      // Hello apple

  // With one exception: braces surrounding arrays within strings allows 
  // constants to be interpreted
  print "Hello {$arr[fruit]}";    // Hello carrot
  print "Hello {$arr['fruit']}";  // Hello apple

  // This will not work, and will result in a parse error, such as:
  // Parse error: parse error, expecting T_STRING' or T_VARIABLE' or 
  // T_NUM_STRING' 
  // This of course applies to using superglobals in strings as well
  print "Hello $arr['fruit']";
  print "Hello $_GET['foo']";

  // Concatenation is another option
  print "Hello " . $arr['fruit']; // Hello apple
?>

When error_reporting is set to show E_NOTICE level errors (by setting it to E_ALL, for example), such uses will become immediately visible. By default, error_reporting is set not to show notices.

As stated in the syntax section, what's inside the square brackets ('[' and ']') must be an expression. This means that code like this works:

<?php
  echo $arr[somefunc($bar)];
?>

This is an example of using a function return value as the array index. PHP also knows about constants:

<?php
  $error_descriptions[E_ERROR]   = "A fatal error has occured";
  $error_descriptions[E_WARNING] = "PHP issued a warning";
  $error_descriptions[E_NOTICE]  = "This is just an informal notice";
?>

Note that E_ERROR is also a valid identifier, just like bar in the first example. But the last example is in fact the same as writing:

<?php
  $error_descriptions[1] = "A fatal error has occured";
  $error_descriptions[2] = "PHP issued a warning";
  $error_descriptions[8] = "This is just an informal notice";
?>

because E_ERROR equals 1, etc.

So why is it bad then?

At some point in the future, the PHP team might want to add another constant or keyword, or a constant in other code may interfere. For example, it is already wrong to use the words empty and default this way, since they are reserved keywords.

    Note: To reiterate, inside a double-quoted string, it's valid to not surround array indexes with quotes so "$foo[bar]" is valid. See the above examples for details on why as well as the section on variable parsing in strings. 

-------------------
Converting to array

For any of the types: integer, float, string, boolean and resource, converting a value to an array results in an array with a single element with index zero and the value of the scalar which was converted. In other words, (array)$scalarValue is exactly the same as array($scalarValue).

If an object is converted to an array, the result is an array whose elements are the object's properties. The keys are the member variable names, with a few notable exceptions: integer properties are unaccessible; private variables have the class name prepended to the variable name; protected variables have a '*' prepended to the variable name. These prepended values have null bytes on either side. This can result in some unexpected behaviour:

<?php

class A {
    private $A; // This will become '\0A\0A'
}

class B extends A {
    private $A; // This will become '\0B\0A'
    public $AA; // This will become 'AA'
}

var_dump((array) new B());
?>

The above will appear to have two keys named 'AA', although one of them is actually named '\0A\0A'.

Converting NULL to an array results in an empty array.
Comparing

It is possible to compare arrays with the array_diff() function and with array operators.
Examples

The array type in PHP is very versatile. Here are some examples:
<?php
// This:
$a = array( 'color' => 'red',
            'taste' => 'sweet',
            'shape' => 'round',
            'name'  => 'apple',
            4        // key will be 0
          );

$b = array('a', 'b', 'c');

// . . .is completely equivalent with this:
$a = array();
$a['color'] = 'red';
$a['taste'] = 'sweet';
$a['shape'] = 'round';
$a['name']  = 'apple';
$a[]        = 4;        // key will be 0

$b = array();
$b[] = 'a';
$b[] = 'b';
$b[] = 'c';

// After the above code is executed, $a will be the array
// array('color' => 'red', 'taste' => 'sweet', 'shape' => 'round', 
// 'name' => 'apple', 0 => 4), and $b will be the array 
// array(0 => 'a', 1 => 'b', 2 => 'c'), or simply array('a', 'b', 'c').
?>

Example #1 Using array()
<?php
// Array as (property-)map
$map = array( 'version'    => 4,
              'OS'         => 'Linux',
              'lang'       => 'english',
              'short_tags' => true
            );
            
// strictly numerical keys
$array = array( 7,
                8,
                0,
                156,
                -10
              );
// this is the same as array(0 => 7, 1 => 8, ...)

$switching = array(         10, // key = 0
                    5    =>  6,
                    3    =>  7, 
                    'a'  =>  4,
                            11, // key = 6 (maximum of integer-indices was 5)
                    '8'  =>  2, // key = 8 (integer!)
                    '02' => 77, // key = '02'
                    0    => 12  // the value 10 will be overwritten by 12
                  );
                  
// empty array
$empty = array();         
?>

Example #2 Collection
<?php
$colors = array('red', 'blue', 'green', 'yellow');

foreach ($colors as $color) {
    echo "Do you like $color?\n";
}

?>

The above example will output:

Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?

Changing the values of the array directly is possible since PHP 5 by passing them by reference. Before that, a workaround is necessary:

Example #3 Changing element in the loop
<?php
// PHP 5
foreach ($colors as &$color) {
    $color = strtoupper($color);
}
unset($color); /* ensure that following writes to
$color will not modify the last array element */

// Workaround for older versions
foreach ($colors as $key => $color) {
    $colors[$key] = strtoupper($color);
}

print_r($colors);
?>

The above example will output:

Array
(
    [0] => RED
    [1] => BLUE
    [2] => GREEN
    [3] => YELLOW
)

This example creates a one-based array.

Example #4 One-based index
<?php
$firstquarter  = array(1 => 'January', 'February', 'March');
print_r($firstquarter);
?>

The above example will output:

Array 
(
    [1] => 'January'
    [2] => 'February'
    [3] => 'March'
)

Example #5 Filling an array
<?php
// fill an array with all items from a directory
$handle = opendir('.');
while (false !== ($file = readdir($handle))) {
    $files[] = $file;
}
closedir($handle); 
?>

Arrays are ordered. The order can be changed using various sorting functions. See the array functions section for more information. The count() function can be used to count the number of items in an array.

Example #6 Sorting an array
<?php
sort($files);
print_r($files);
?>

Because the value of an array can be anything, it can also be another array. This enables the creation of recursive and multi-dimensional arrays.

Example #7 Recursive and multi-dimensional arrays
<?php
$fruits = array ( "fruits"  => array ( "a" => "orange",
                                       "b" => "banana",
                                       "c" => "apple"
                                     ),
                  "numbers" => array ( 1,
                                       2,
                                       3,
                                       4,
                                       5,
                                       6
                                     ),
                  "holes"   => array (      "first",
                                       5 => "second",
                                            "third"
                                     )
                );

// Some examples to address values in the array above 
echo $fruits["holes"][5];    // prints "second"
echo $fruits["fruits"]["a"]; // prints "orange"
unset($fruits["holes"][0]);  // remove "first"

// Create a new multi-dimensional array
$juices["apple"]["green"] = "good"; 
?>

Array assignment always involves value copying. Use the reference operator to copy an array by reference.
<?php
$arr1 = array(2, 3);
$arr2 = $arr1;
$arr2[] = 4; // $arr2 is changed,
             // $arr1 is still array(2, 3)
             
$arr3 = &$arr1;
$arr3[] = 4; // now $arr1 and $arr3 are the same
?>

=====================================================================


Objects
Object Initialization

To create a new object, use the new statement to instantiate a class:
<?php
class foo
{
    function do_foo()
    {
        echo "Doing foo."; 
    }
}

$bar = new foo;
$bar->do_foo();
?>

For a full discussion, see the Classes and Objects chapter.
Converting to object

If an object is converted to an object, it is not modified. If a value of any other type is converted to an object, a new instance of the stdClass built-in class is created. If the value was NULL, the new instance will be empty. Arrays convert to an object with properties named by keys, and corresponding values. For any other value, a member variable named scalar will contain the value.
<?php
$obj = (object) 'ciao';
echo $obj->scalar;  // outputs 'ciao'
?>

=====================================================================


Resources

A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions. See the appendix for a listing of all these functions and the corresponding resource types.

    Note: The resource type was introduced in PHP 4 

See also the get_resource_type() function.
Converting to resource

As resource variables hold special handlers to opened files, database connections, image canvas areas and the like, converting to a resource makes no sense.
Freeing resources

Thanks to the reference-counting system introduced with PHP 4's Zend Engine, a resource with no more references to it is detected automatically, and it is freed by the garbage collector. For this reason, it is rarely necessary to free the memory manually.

    Note: Persistent database links are an exception to this rule. They are not destroyed by the garbage collector. See the persistent connections section for more information. 

=====================================================================


NULL

The special NULL value represents a variable with no value. NULL is the only possible value of type NULL.

    Note: The null type was introduced in PHP 4. 

A variable is considered to be null if:

    *

      it has been assigned the constant NULL.
    *

      it has not been set to any value yet.
    *

      it has been unset().

Syntax

There is only one value of type null, and that is the case-insensitive keyword NULL.
<?php
$var = NULL;       
?>

See also the functions is_null() and unset().
Casting to NULL

Casting a variable to null will remove the variable and unset its value.

=====================================================================


Pseudo-types and variables used in this documentation
mixed

mixed indicates that a parameter may accept multiple (but not necessarily all) types.

gettype() for example will accept all PHP types, while str_replace() will accept strings and arrays.
number

number indicates that a parameter can be either integer or float.
callback

Some functions like call_user_func() or usort() accept user-defined callback functions as a parameter. Callback functions can not only be simple functions, but also object methods, including static class methods.

A PHP function is passed by its name as a string. Any built-in or user-defined function can be used, except language constructs such as: array(), echo(), empty(), eval(), exit(), isset(), list(), print() or unset().

A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1.

Static class methods can also be passed without instantiating an object of that class by passing the class name instead of an object at index 0.

Apart from common user-defined function, create_function() can also be used to create an anonymous callback function. As of PHP 5.3.0 it is possible to also pass a closure to a callback parameter.

Example #1 Callback function examples
<?php 

// An example callback function
function my_callback_function() {
    echo 'hello world!';
}

// An example callback method
class MyClass {
    static function myCallbackMethod() {
        echo 'Hello World!';
    }
}

// Type 1: Simple callback
call_user_func('my_callback_function'); 

// Type 2: Static class method call
call_user_func(array('MyClass', 'myCallbackMethod')); 

// Type 3: Object method call
$obj = new MyClass();
call_user_func(array($obj, 'myCallbackMethod'));

// Type 4: Static class method call (As of PHP 5.2.3)
call_user_func('MyClass::myCallbackMethod');

// Type 5: Relative static class method call (As of PHP 5.3.0)
class A {
    public static function who() {
        echo "A\n";
    }
}

class B extends A {
    public static function who() {
        echo "B\n";
    }
}

call_user_func(array('B', 'parent::who')); // A
?>

Example #2 Callback example using a Closure
<?php
// Our closure
$double = function($a) {
    return $a * 2;
};

// This is our range of numbers
$numbers = range(1, 5);

// Use the closure as a callback here to 
// double the size of each element in our 
// range
$new_numbers = array_map($double, $numbers);

print implode(' ', $new_numbers);
?>

The above example will output:

2 4 6 8 10

    Note: In PHP4, it was necessary to use a reference to create a callback that points to the actual object, and not a copy of it. For more details, see References Explained. 

    Note:

    Callbacks registered with functions such as call_user_func() and call_user_func_array() will not be called if there is an uncaught exception thrown in a previous callback.

void

void as a return type means that the return value is useless. void in a parameter list means that the function doesn't accept any parameters.
...

$... in function prototypes means and so on. This variable name is used when a function can take an endless number of arguments.

=====================================================================


Type Juggling

PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which the variable is used. That is to say, if a string value is assigned to variable $var, $var becomes a string. If an integer value is then assigned to $var, it becomes an integer.

An example of PHP's automatic type conversion is the addition operator '+'. If either operand is a float, then both operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer. Note that this does not change the types of the operands themselves; the only change is in how the operands are evaluated and what the type of the expression itself is.
<?php
$foo = "0";  // $foo is string (ASCII 48)
$foo += 2;   // $foo is now an integer (2)
$foo = $foo + 1.3;  // $foo is now a float (3.3)
$foo = 5 + "10 Little Piggies"; // $foo is integer (15)
$foo = 5 + "10 Small Pigs";     // $foo is integer (15)
?>

If the last two examples above seem odd, see String conversion to numbers.

To force a variable to be evaluated as a certain type, see the section on Type casting. To change the type of a variable, see the settype() function.

To test any of the examples in this section, use the var_dump() function.

    Note:

    The behaviour of an automatic conversion to array is currently undefined.

    Also, because PHP supports indexing into strings via offsets using the same syntax as array indexing, the following example holds true for all PHP versions:
    <?php
    $a    = 'car'; // $a is a string
    $a[0] = 'b';   // $a is still a string
    echo $a;       // bar
    ?>

    See the section titled String access by character for more information.

Type Casting

Type casting in PHP works much as it does in C: the name of the desired type is written in parentheses before the variable which is to be cast.
<?php
$foo = 10;   // $foo is an integer
$bar = (boolean) $foo;   // $bar is a boolean
?>

The casts allowed are:

    * (int), (integer) - cast to integer
    * (bool), (boolean) - cast to boolean
    * (float), (double), (real) - cast to float
    * (string) - cast to string
    * (array) - cast to array
    * (object) - cast to object
    * (unset) - cast to NULL (PHP 5)

(binary) casting and b prefix forward support was added in PHP 5.2.1

Note that tabs and spaces are allowed inside the parentheses, so the following are functionally equivalent:
<?php
$foo = (int) $bar;
$foo = ( int ) $bar;
?>

Casting literal strings and variables to binary strings:
<?php
$binary = (binary) $string;
$binary = b"binary string";
?>

    Note:

    Instead of casting a variable to a string, it is also possible to enclose the variable in double quotes.
    <?php
    $foo = 10;            // $foo is an integer
    $str = "$foo";        // $str is a string
    $fst = (string) $foo; // $fst is also a string

    // This prints out that "they are the same"
    if ($fst === $str) {
        echo "they are the same";
    }
    ?>

It may not be obvious exactly what will happen when casting between certain types. For more information, see these sections:

    * Converting to boolean
    * Converting to integer
    * Converting to float
    * Converting to string
    * Converting to array
    * Converting to object
    * Converting to resource
    * Converting to NULL
    * The type comparison tables

=====================================================================
=====================================================================
    * Variables
=====================================================================


Basics

Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive.

Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'

    Note: For our purposes here, a letter is a-z, A-Z, and the bytes from 127 through 255 (0x7f-0xff). 

    Note: $this is a special variable that can't be assigned. 

Tip

See also the Userland Naming Guide.

For information on variable related functions, see the Variable Functions Reference.

<?php
$var = 'Bob';
$Var = 'Joe';
echo "$var, $Var";      // outputs "Bob, Joe"

$4site = 'not yet';     // invalid; starts with a number
$_4site = 'not yet';    // valid; starts with an underscore
$täyte = 'mansikka';    // valid; 'ä' is (Extended) ASCII 228.
?>

By default, variables are always assigned by value. That is to say, when you assign an expression to a variable, the entire value of the original expression is copied into the destination variable. This means, for instance, that after assigning one variable's value to another, changing one of those variables will have no effect on the other. For more information on this kind of assignment, see the chapter on Expressions.

PHP also offers another way to assign values to variables: assign by reference. This means that the new variable simply references (in other words, "becomes an alias for" or "points to") the original variable. Changes to the new variable affect the original, and vice versa.

To assign by reference, simply prepend an ampersand (&) to the beginning of the variable which is being assigned (the source variable). For instance, the following code snippet outputs 'My name is Bob' twice:
<?php
$foo = 'Bob';              // Assign the value 'Bob' to $foo
$bar = &$foo;              // Reference $foo via $bar.
$bar = "My name is $bar";  // Alter $bar...
echo $bar;
echo $foo;                 // $foo is altered too.
?>

One important thing to note is that only named variables may be assigned by reference.
<?php
$foo = 25;
$bar = &$foo;      // This is a valid assignment.
$bar = &(24 * 7);  // Invalid; references an unnamed expression.

function test()
{
   return 25;
}

$bar = &test();    // Invalid.
?>

It is not necessary to initialize variables in PHP however it is a very good practice. Uninitialized variables have a default value of their type depending on the context in which they are used - booleans default to FALSE, integers and floats default to zero, strings (e.g. used in echo()) are set as an empty string and arrays become to an empty array.

Example #1 Default values of uninitialized variables
<?php
// Unset AND unreferenced (no use context) variable; outputs NULL
var_dump($unset_var);

// Boolean usage; outputs 'false' (See ternary operators for more on this syntax)
echo($unset_bool ? "true\n" : "false\n");

// String usage; outputs 'string(3) "abc"'
$unset_str .= 'abc';
var_dump($unset_str);

// Integer usage; outputs 'int(25)'
$unset_int += 25; // 0 + 25 => 25
var_dump($unset_int);

// Float/double usage; outputs 'float(1.25)'
$unset_float += 1.25;
var_dump($unset_float);

// Array usage; outputs array(1) {  [3]=>  string(3) "def" }
$unset_arr[3] = "def"; // array() + array(3 => "def") => array(3 => "def")
var_dump($unset_arr);

// Object usage; creates new stdClass object (see http://www.php.net/manual/en/reserved.classes.php)
// Outputs: object(stdClass)#1 (1) {  ["foo"]=>  string(3) "bar" }
$unset_obj->foo = 'bar';
var_dump($unset_obj);
?>

Relying on the default value of an uninitialized variable is problematic in the case of including one file into another which uses the same variable name. It is also a major security risk with register_globals turned on. E_NOTICE level error is issued in case of working with uninitialized variables, however not in the case of appending elements to the uninitialized array. isset() language construct can be used to detect if a variable has been already initialized.

=====================================================================


Predefined Variables

PHP provides a large number of predefined variables to any script which it runs. Many of these variables, however, cannot be fully documented as they are dependent upon which server is running, the version and setup of the server, and other factors. Some of these variables will not be available when PHP is run on the command line. For a listing of these variables, please see the section on Reserved Predefined Variables.
Warning

In PHP 4.2.0 and later, the default value for the PHP directive register_globals is off. This is a major change in PHP. Having register_globals off affects the set of predefined variables available in the global scope. For example, to get DOCUMENT_ROOT you'll use $_SERVER['DOCUMENT_ROOT'] instead of $DOCUMENT_ROOT, or $_GET['id'] from the URL http://www.example.com/test.php?id=3 instead of $id, or $_ENV['HOME'] instead of $HOME.

For related information on this change, read the configuration entry for register_globals, the security chapter on Using Register Globals , as well as the PHP » 4.1.0 and » 4.2.0 Release Announcements.

Using the available PHP Reserved Predefined Variables, like the superglobal arrays, is preferred.

From version 4.1.0 onward, PHP provides an additional set of predefined arrays containing variables from the web server (if applicable), the environment, and user input. These new arrays are rather special in that they are automatically global--i.e., automatically available in every scope. For this reason, they are often known as "superglobals". (There is no mechanism in PHP for user-defined superglobals.) The superglobals are listed below; however, for a listing of their contents and further discussion on PHP predefined variables and their natures, please see the section Reserved Predefined Variables. Also, you'll notice how the older predefined variables ($HTTP_*_VARS) still exist. As of PHP 5.0.0, the long PHP predefined variable arrays may be disabled with the register_long_arrays directive.

    Note: Variable variables

    Superglobals cannot be used as variable variables inside functions or class methods.

    Note:

    Even though both the superglobal and HTTP_*_VARS can exist at the same time; they are not identical, so modifying one will not change the other.

If certain variables in variables_order are not set, their appropriate PHP predefined arrays are also left empty.

=====================================================================


Variable scope

The scope of a variable is the context within which it is defined. For the most part all PHP variables only have a single scope. This single scope spans included and required files as well. For example:
<?php
$a = 1;
include 'b.inc';
?>

Here the $a variable will be available within the included b.inc script. However, within user-defined functions a local function scope is introduced. Any variable used inside a function is by default limited to the local function scope. For example:
<?php
$a = 1; /* global scope */ 

function test()
{ 
    echo $a; /* reference to local scope variable */ 
} 

test();
?>

This script will not produce any output because the echo statement refers to a local version of the $a variable, and it has not been assigned a value within this scope. You may notice that this is a little bit different from the C language in that global variables in C are automatically available to functions unless specifically overridden by a local definition. This can cause some problems in that people may inadvertently change a global variable. In PHP global variables must be declared global inside a function if they are going to be used in that function.
The global keyword

First, an example use of global:

Example #1 Using global
<?php
$a = 1;
$b = 2;

function Sum()
{
    global $a, $b;

    $b = $a + $b;
} 

Sum();
echo $b;
?>

The above script will output 3. By declaring $a and $b global within the function, all references to either variable will refer to the global version. There is no limit to the number of global variables that can be manipulated by a function.

A second way to access variables from the global scope is to use the special PHP-defined $GLOBALS array. The previous example can be rewritten as:

Example #2 Using $GLOBALS instead of global
<?php
$a = 1;
$b = 2;

function Sum()
{
    $GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
} 

Sum();
echo $b;
?>

The $GLOBALS array is an associative array with the name of the global variable being the key and the contents of that variable being the value of the array element. Notice how $GLOBALS exists in any scope, this is because $GLOBALS is a superglobal. Here's an example demonstrating the power of superglobals:

Example #3 Example demonstrating superglobals and scope
<?php
function test_global()
{
    // Most predefined variables aren't "super" and require 
    // 'global' to be available to the functions local scope.
    global $HTTP_POST_VARS;
    
    echo $HTTP_POST_VARS['name'];
    
    // Superglobals are available in any scope and do 
    // not require 'global'. Superglobals are available 
    // as of PHP 4.1.0, and HTTP_POST_VARS is now
    // deemed deprecated.
    echo $_POST['name'];
}
?>

    Note:

    Using global keyword outside a function is not an error. It can be used if the file is included from inside a function.

Using static variables

Another important feature of variable scoping is the static variable. A static variable exists only in a local function scope, but it does not lose its value when program execution leaves this scope. Consider the following example:

Example #4 Example demonstrating need for static variables
<?php
function test()
{
    $a = 0;
    echo $a;
    $a++;
}
?>

This function is quite useless since every time it is called it sets $a to 0 and prints 0. The $a++ which increments the variable serves no purpose since as soon as the function exits the $a variable disappears. To make a useful counting function which will not lose track of the current count, the $a variable is declared static:

Example #5 Example use of static variables
<?php
function test()
{
    static $a = 0;
    echo $a;
    $a++;
}
?>

Now, $a is initialized only in first call of function and every time the test() function is called it will print the value of $a and increment it.

Static variables also provide one way to deal with recursive functions. A recursive function is one which calls itself. Care must be taken when writing a recursive function because it is possible to make it recurse indefinitely. You must make sure you have an adequate way of terminating the recursion. The following simple function recursively counts to 10, using the static variable $count to know when to stop:

Example #6 Static variables with recursive functions
<?php
function test()
{
    static $count = 0;

    $count++;
    echo $count;
    if ($count < 10) {
        test();
    }
    $count--;
}
?>

    Note:

    Static variables may be declared as seen in the examples above. Trying to assign values to these variables which are the result of expressions will cause a parse error.

    Example #7 Declaring static variables
    <?php
    function foo(){
        static $int = 0;          // correct 
        static $int = 1+2;        // wrong  (as it is an expression)
        static $int = sqrt(121);  // wrong  (as it is an expression too)

        $int++;
        echo $int;
    }
    ?>

    Note:

    Static declarations are resolved in compile-time.

    Note:

    Using global keyword outside a function is not an error. It can be used if the file is included from inside a function.

References with global and static variables

The Zend Engine 1, driving PHP 4, implements the static and global modifier for variables in terms of references. For example, a true global variable imported inside a function scope with the global statement actually creates a reference to the global variable. This can lead to unexpected behaviour which the following example addresses:
<?php
function test_global_ref() {
    global $obj;
    $obj = &new stdclass;
}

function test_global_noref() {
    global $obj;
    $obj = new stdclass;
}

test_global_ref();
var_dump($obj);
test_global_noref();
var_dump($obj);
?>

The above example will output:

NULL
object(stdClass)(0) {
}

A similar behaviour applies to the static statement. References are not stored statically:
<?php
function &get_instance_ref() {
    static $obj;

    echo 'Static object: ';
    var_dump($obj);
    if (!isset($obj)) {
        // Assign a reference to the static variable
        $obj = &new stdclass;
    }
    $obj->property++;
    return $obj;
}

function &get_instance_noref() {
    static $obj;

    echo 'Static object: ';
    var_dump($obj);
    if (!isset($obj)) {
        // Assign the object to the static variable
        $obj = new stdclass;
    }
    $obj->property++;
    return $obj;
}

$obj1 = get_instance_ref();
$still_obj1 = get_instance_ref();
echo "\n";
$obj2 = get_instance_noref();
$still_obj2 = get_instance_noref();
?>

The above example will output:

Static object: NULL
Static object: NULL

Static object: NULL
Static object: object(stdClass)(1) {
["property"]=>
int(1)
}

This example demonstrates that when assigning a reference to a static variable, it's not remembered when you call the &get_instance_ref() function a second time.

=====================================================================


Variable variables

Sometimes it is convenient to be able to have variable variable names. That is, a variable name which can be set and used dynamically. A normal variable is set with a statement such as:
<?php
$a = 'hello';
?>

A variable variable takes the value of a variable and treats that as the name of a variable. In the above example, hello, can be used as the name of a variable by using two dollar signs. i.e.
<?php
$$a = 'world';
?>

At this point two variables have been defined and stored in the PHP symbol tree: $a with contents "hello" and $hello with contents "world". Therefore, this statement:
<?php
echo "$a ${$a}";
?>

produces the exact same output as:
<?php
echo "$a $hello";
?>

i.e. they both produce: hello world.

In order to use variable variables with arrays, you have to resolve an ambiguity problem. That is, if you write $$a[1] then the parser needs to know if you meant to use $a[1] as a variable, or if you wanted $$a as the variable and then the [1] index from that variable. The syntax for resolving this ambiguity is: ${$a[1]} for the first case and ${$a}[1] for the second.

Class properties may also be accessed using variable property names. The variable property name will be resolved within the scope from which the call is made. For instance, if you have an expression such as $foo->$bar, then the local scope will be examined for $bar and its value will be used as the name of the property of $foo. This is also true if $bar is an array access.

Example #1 Variable function example
<?php
class foo {
    var $bar = 'I am bar.';
}

$foo = new foo();
$bar = 'bar';
$baz = array('foo', 'bar', 'baz', 'quux');
echo $foo->$bar . "\n";
echo $foo->$baz[1] . "\n";
?>

The above example will output:

I am bar.
I am bar.
Warning

Please note that variable variables cannot be used with PHP's Superglobal arrays within functions or class methods. The variable $this is also a special variable that cannot be referenced dynamically.

=====================================================================


Variables From External Sources
HTML Forms (GET and POST)

When a form is submitted to a PHP script, the information from that form is automatically made available to the script. There are many ways to access this information, for example:

Example #1 A simple HTML form

<form action="foo.php" method="post">
    Name:  <input type="text" name="username" /><br />
    Email: <input type="text" name="email" /><br />
    <input type="submit" name="submit" value="Submit me!" />
</form>

Depending on your particular setup and personal preferences, there are many ways to access data from your HTML forms. Some examples are:

Example #2 Accessing data from a simple POST HTML form
<?php 
// Available since PHP 4.1.0

   echo $_POST['username'];
   echo $_REQUEST['username'];

   import_request_variables('p', 'p_');
   echo $p_username;

// As of PHP 5.0.0, these long predefined variables can be
// disabled with the register_long_arrays directive.

   echo $HTTP_POST_VARS['username'];

// Available if the PHP directive register_globals = on. As of 
// PHP 4.2.0 the default value of register_globals = off.
// Using/relying on this method is not preferred.

   echo $username;
?>

Using a GET form is similar except you'll use the appropriate GET predefined variable instead. GET also applies to the QUERY_STRING (the information after the '?' in a URL). So, for example, http://www.example.com/test.php?id=3 contains GET data which is accessible with $_GET['id']. See also $_REQUEST and import_request_variables().

    Note:

    Superglobal arrays, like $_POST and $_GET, became available in PHP 4.1.0

    Note:

    Dots and spaces in variable names are converted to underscores. For example <input name="a.b" /> becomes $_REQUEST["a_b"].

As shown, before PHP 4.2.0 the default value for register_globals was on. The PHP community is encouraging all to not rely on this directive as it's preferred to assume it's off and code accordingly.

    Note:

    The magic_quotes_gpc configuration directive affects Get, Post and Cookie values. If turned on, value (It's "PHP!") will automagically become (It\'s \"PHP!\"). Escaping is needed for DB insertion. See also addslashes(), stripslashes() and magic_quotes_sybase.

PHP also understands arrays in the context of form variables (see the related faq). You may, for example, group related variables together, or use this feature to retrieve values from a multiple select input. For example, let's post a form to itself and upon submission display the data:

Example #3 More complex form variables
<?php
if ($_POST) {
    echo '<pre>';
    echo htmlspecialchars(print_r($_POST, true));
    echo '</pre>';
}
?>
<form action="" method="post">
    Name:  <input type="text" name="personal[name]" /><br />
    Email: <input type="text" name="personal[email]" /><br />
    Beer: <br />
    <select multiple name="beer[]">
        <option value="warthog">Warthog</option>
        <option value="guinness">Guinness</option>
        <option value="stuttgarter">Stuttgarter Schwabenbräu</option>
    </select><br />
    <input type="submit" value="submit me!" />
</form>
IMAGE SUBMIT variable names

When submitting a form, it is possible to use an image instead of the standard submit button with a tag like:

<input type="image" src="image.gif" name="sub" />

When the user clicks somewhere on the image, the accompanying form will be transmitted to the server with two additional variables, sub_x and sub_y. These contain the coordinates of the user click within the image. The experienced may note that the actual variable names sent by the browser contains a period rather than an underscore, but PHP converts the period to an underscore automatically.
HTTP Cookies

PHP transparently supports HTTP cookies as defined by » Netscape's Spec. Cookies are a mechanism for storing data in the remote browser and thus tracking or identifying return users. You can set cookies using the setcookie() function. Cookies are part of the HTTP header, so the SetCookie function must be called before any output is sent to the browser. This is the same restriction as for the header() function. Cookie data is then available in the appropriate cookie data arrays, such as $_COOKIE, $HTTP_COOKIE_VARS as well as in $_REQUEST. See the setcookie() manual page for more details and examples.

If you wish to assign multiple values to a single cookie variable, you may assign it as an array. For example:
<?php
  setcookie("MyCookie[foo]", 'Testing 1', time()+3600);
  setcookie("MyCookie[bar]", 'Testing 2', time()+3600);
?>

That will create two separate cookies although MyCookie will now be a single array in your script. If you want to set just one cookie with multiple values, consider using serialize() or explode() on the value first.

Note that a cookie will replace a previous cookie by the same name in your browser unless the path or domain is different. So, for a shopping cart application you may want to keep a counter and pass this along. i.e.

Example #4 A setcookie() example
<?php
if (isset($_COOKIE['count'])) {
    $count = $_COOKIE['count'] + 1;
} else {
    $count = 1;
}
setcookie('count', $count, time()+3600);
setcookie("Cart[$count]", $item, time()+3600);
?>
Dots in incoming variable names

Typically, PHP does not alter the names of variables when they are passed into a script. However, it should be noted that the dot (period, full stop) is not a valid character in a PHP variable name. For the reason, look at it:
<?php
$varname.ext;  /* invalid variable name */
?>
Now, what the parser sees is a variable named $varname, followed by the string concatenation operator, followed by the barestring (i.e. unquoted string which doesn't match any known key or reserved words) 'ext'. Obviously, this doesn't have the intended result.

For this reason, it is important to note that PHP will automatically replace any dots in incoming variable names with underscores.
Determining variable types

Because PHP determines the types of variables and converts them (generally) as needed, it is not always obvious what type a given variable is at any one time. PHP includes several functions which find out what type a variable is, such as: gettype(), is_array(), is_float(), is_int(), is_object(), and is_string(). See also the chapter on Types.

=====================================================================
=====================================================================
    * Constants
=====================================================================

Table of Contents

    * Syntax
    * Magic constants

A constant is an identifier (name) for a simple value. As the name suggests, that value cannot change during the execution of the script (except for magic constants, which aren't actually constants). A constant is case-sensitive by default. By convention, constant identifiers are always uppercase.

The name of a constant follows the same rules as any label in PHP. A valid constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thusly: [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*
Tip

See also the Userland Naming Guide.

Example #1 Valid and invalid constant names
<?php

// Valid constant names
define("FOO",     "something");
define("FOO2",    "something else");
define("FOO_BAR", "something more");

// Invalid constant names
define("2FOO",    "something");

// This is valid, but should be avoided:
// PHP may one day provide a magical constant
// that will break your script
define("__FOO__", "something"); 

?>

    Note: For our purposes here, a letter is a-z, A-Z, and the ASCII characters from 127 through 255 (0x7f-0xff). 

Like superglobals, the scope of a constant is global. You can access constants anywhere in your script without regard to scope. For more information on scope, read the manual section on variable scope.

=====================================================================


Syntax

You can define a constant by using the define()-function or by using the const keyword outside a class definition as of PHP 5.3.0. Once a constant is defined, it can never be changed or undefined.

Only scalar data (boolean, integer, float and string) can be contained in constants. It is possible to define constants as a resource, but it should be avoided, as it can cause unexpected results.

You can get the value of a constant by simply specifying its name. Unlike with variables, you should not prepend a constant with a $. You can also use the function constant() to read a constant's value if you wish to obtain the constant's name dynamically. Use get_defined_constants() to get a list of all defined constants.

    Note: Constants and (global) variables are in a different namespace. This implies that for example TRUE and $TRUE are generally different. 

If you use an undefined constant, PHP assumes that you mean the name of the constant itself, just as if you called it as a string (CONSTANT vs "CONSTANT"). An error of level E_NOTICE will be issued when this happens. See also the manual entry on why $foo[bar] is wrong (unless you first define() bar as a constant). If you simply want to check if a constant is set, use the defined() function.

These are the differences between constants and variables:

    * Constants do not have a dollar sign ($) before them;
    * Constants may only be defined using the define() function, not by simple assignment;
    * Constants may be defined and accessed anywhere without regard to variable scoping rules;
    * Constants may not be redefined or undefined once they have been set; and
    * Constants may only evaluate to scalar values.

Example #1 Defining Constants
<?php
define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.
?>

Example #2 Defining Constants using the const keyword
<?php
// Works as of PHP 5.3.0
const CONSTANT = 'Hello World';

echo CONSTANT;
?>

    Note:

    As opposed to defining constants using define(), constants defined using the const keyword must be declared at the top-level scope because they are defined at compile-time. This means that they cannot be declared inside functions, loops or if statements.

See also Class Constants.

=====================================================================


Magic constants

PHP provides a large number of predefined constants to any script which it runs. Many of these constants, however, are created by various extensions, and will only be present when those extensions are available, either via dynamic loading or because they have been compiled in.

There are seven magical constants that change depending on where they are used. For example, the value of __LINE__ depends on the line that it's used on in your script. These special constants are case-insensitive and are as follows:

A few "magical" PHP constants Name 	Description
__LINE__ 	The current line number of the file.
__FILE__ 	The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances.
__DIR__ 	The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory. (Added in PHP 5.3.0.)
__FUNCTION__ 	The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__CLASS__ 	The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.
__METHOD__ 	The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive).
__NAMESPACE__ 	The name of the current namespace (case-sensitive). This constant is defined in compile-time (Added in PHP 5.3.0).

See also get_class(), get_object_vars(), file_exists() and function_exists().

=====================================================================
=====================================================================
    * Expressions
=====================================================================


Expressions

Expressions are the most important building stones of PHP. In PHP, almost anything you write is an expression. The simplest yet most accurate way to define an expression is "anything that has a value".

The most basic forms of expressions are constants and variables. When you type "$a = 5", you're assigning '5' into $a. '5', obviously, has the value 5, or in other words '5' is an expression with the value of 5 (in this case, '5' is an integer constant).

After this assignment, you'd expect $a's value to be 5 as well, so if you wrote $b = $a, you'd expect it to behave just as if you wrote $b = 5. In other words, $a is an expression with the value of 5 as well. If everything works right, this is exactly what will happen.

Slightly more complex examples for expressions are functions. For instance, consider the following function:
<?php
function foo ()
{
    return 5;
}
?>

Assuming you're familiar with the concept of functions (if you're not, take a look at the chapter about functions), you'd assume that typing $c = foo() is essentially just like writing $c = 5, and you're right. Functions are expressions with the value of their return value. Since foo() returns 5, the value of the expression 'foo()' is 5. Usually functions don't just return a static value but compute something.

Of course, values in PHP don't have to be integers, and very often they aren't. PHP supports four scalar value types: integer values, floating point values (float), string values and boolean values (scalar values are values that you can't 'break' into smaller pieces, unlike arrays, for instance). PHP also supports two composite (non-scalar) types: arrays and objects. Each of these value types can be assigned into variables or returned from functions.

PHP takes expressions much further, in the same way many other languages do. PHP is an expression-oriented language, in the sense that almost everything is an expression. Consider the example we've already dealt with, '$a = 5'. It's easy to see that there are two values involved here, the value of the integer constant '5', and the value of $a which is being updated to 5 as well. But the truth is that there's one additional value involved here, and that's the value of the assignment itself. The assignment itself evaluates to the assigned value, in this case 5. In practice, it means that '$a = 5', regardless of what it does, is an expression with the value 5. Thus, writing something like '$b = ($a = 5)' is like writing '$a = 5; $b = 5;' (a semicolon marks the end of a statement). Since assignments are parsed in a right to left order, you can also write '$b = $a = 5'.

Another good example of expression orientation is pre- and post-increment and decrement. Users of PHP and many other languages may be familiar with the notation of variable++ and variable--. These are increment and decrement operators. In PHP, like in C, there are two types of increment - pre-increment and post-increment. Both pre-increment and post-increment essentially increment the variable, and the effect on the variable is identical. The difference is with the value of the increment expression. Pre-increment, which is written '++$variable', evaluates to the incremented value (PHP increments the variable before reading its value, thus the name 'pre-increment'). Post-increment, which is written '$variable++' evaluates to the original value of $variable, before it was incremented (PHP increments the variable after reading its value, thus the name 'post-increment').

A very common type of expressions are comparison expressions. These expressions evaluate to either FALSE or TRUE. PHP supports > (bigger than), >= (bigger than or equal to), == (equal), != (not equal), < (smaller than) and <= (smaller than or equal to). The language also supports a set of strict equivalence operators: === (equal to and same type) and !== (not equal to or not same type). These expressions are most commonly used inside conditional execution, such as if statements.

The last example of expressions we'll deal with here is combined operator-assignment expressions. You already know that if you want to increment $a by 1, you can simply write '$a++' or '++$a'. But what if you want to add more than one to it, for instance 3? You could write '$a++' multiple times, but this is obviously not a very efficient or comfortable way. A much more common practice is to write '$a = $a + 3'. '$a + 3' evaluates to the value of $a plus 3, and is assigned back into $a, which results in incrementing $a by 3. In PHP, as in several other languages like C, you can write this in a shorter way, which with time would become clearer and quicker to understand as well. Adding 3 to the current value of $a can be written '$a += 3'. This means exactly "take the value of $a, add 3 to it, and assign it back into $a". In addition to being shorter and clearer, this also results in faster execution. The value of '$a += 3', like the value of a regular assignment, is the assigned value. Notice that it is NOT 3, but the combined value of $a plus 3 (this is the value that's assigned into $a). Any two-place operator can be used in this operator-assignment mode, for example '$a -= 5' (subtract 5 from the value of $a), '$b *= 7' (multiply the value of $b by 7), etc.

There is one more expression that may seem odd if you haven't seen it in other languages, the ternary conditional operator:

<?php
$first ? $second : $third
?>

If the value of the first subexpression is TRUE (non-zero), then the second subexpression is evaluated, and that is the result of the conditional expression. Otherwise, the third subexpression is evaluated, and that is the value.

The following example should help you understand pre- and post-increment and expressions in general a bit better:

<?php
function double($i)
{
    return $i*2;
}
$b = $a = 5;        /* assign the value five into the variable $a and $b */
$c = $a++;          /* post-increment, assign original value of $a 
                       (5) to $c */
$e = $d = ++$b;     /* pre-increment, assign the incremented value of 
                       $b (6) to $d and $e */

/* at this point, both $d and $e are equal to 6 */

$f = double($d++);  /* assign twice the value of $d before
                       the increment, 2*6 = 12 to $f */
$g = double(++$e);  /* assign twice the value of $e after
                       the increment, 2*7 = 14 to $g */
$h = $g += 10;      /* first, $g is incremented by 10 and ends with the 
                       value of 24. the value of the assignment (24) is 
                       then assigned into $h, and $h ends with the value 
                       of 24 as well. */
?>

Some expressions can be considered as statements. In this case, a statement has the form of 'expr ;' that is, an expression followed by a semicolon. In '$b = $a = 5;', '$a = 5' is a valid expression, but it's not a statement by itself. '$b = $a = 5;' however is a valid statement.

One last thing worth mentioning is the truth value of expressions. In many events, mainly in conditional execution and loops, you're not interested in the specific value of the expression, but only care about whether it means TRUE or FALSE. The constants TRUE and FALSE (case-insensitive) are the two possible boolean values. When necessary, an expression is automatically converted to boolean. See the section about type-casting for details about how.

PHP provides a full and powerful implementation of expressions, and documenting it entirely goes beyond the scope of this manual. The above examples should give you a good idea about what expressions are and how you can construct useful expressions. Throughout the rest of this manual we'll write expr to indicate any valid PHP expression.

=====================================================================
=====================================================================
    * Operators
=====================================================================

Table of Contents

    * Operator Precedence
    * Arithmetic Operators
    * Assignment Operators
    * Bitwise Operators
    * Comparison Operators
    * Error Control Operators
    * Execution Operators
    * Incrementing/Decrementing Operators
    * Logical Operators
    * String Operators
    * Array Operators
    * Type Operators

An operator is something that takes one or more values (or expressions, in programming jargon) and yields another value (so that the construction itself becomes an expression).

Operators can be grouped according to the number of values they take. Unary operators take only one value, for example ! (the logical not operator) or ++ (the increment operator). Binary operators take two values, such as the familiar arithmetical operators + (plus) and - (minus), and the majority of PHP operators fall into this category. Finally, there is a single ternary operator, ? :, which takes three values; this is usually referred to simply as "the ternary operator" (although it could perhaps more properly be called the conditional operator).

A full list of PHP operators follows in the section Operator Precedence. This also explains operator Presedence and Associativity, which govern exactly how expressions containing several different operators are evaluated. 

=====================================================================


Operator Precedence

The precedence of an operator specifies how "tightly" it binds two expressions together. For example, in the expression 1 + 5 * 3, the answer is 16 and not 18 because the multiplication ("*") operator has a higher precedence than the addition ("+") operator. Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18.

When operators have equal precedence, their associativity decides whether they are evaluated starting from the right, or starting from the left - see the examples below.

The following table lists the operators in order of precedence, with the highest-precedence ones at the top. Operators on the same line have equal precedence, in which case associativity decides the order of evaluation.
Operator Precedence Associativity 	Operators 	Additional Information
non-associative 	clone new 	clone and new
left 	[ 	array()
non-associative 	++ -- 	increment/decrement
right 	~ - (int) (float) (string) (array) (object) (bool) @ 	types
non-associative 	instanceof 	types
right 	! 	logical
left 	* / % 	arithmetic
left 	+ - . 	arithmetic and string
left 	<< >> 	bitwise
non-associative 	< <= > >= <> 	comparison
non-associative 	== != === !== 	comparison
left 	& 	bitwise and references
left 	^ 	bitwise
left 	| 	bitwise
left 	&& 	logical
left 	|| 	logical
left 	? : 	ternary
right 	= += -= *= /= .= %= &= |= ^= <<= >>= => 	assignment
left 	and 	logical
left 	xor 	logical
left 	or 	logical
left 	, 	many uses

For operators of equal precedence, left associativity means that evaluation proceeds from left to right, and right associativity means the opposite.

Example #1 Associativity
<?php
$a = 3 * 3 % 5; // (3 * 3) % 5 = 4
$a = true ? 0 : true ? 1 : 2; // (true ? 0 : true) ? 1 : 2 = 2

$a = 1;
$b = 2;
$a = $b += 3; // $a = ($b += 3) -> $a = 5, $b = 5

// mixing ++ and + produces undefined behavior
$a = 1;
echo ++$a + $a++; // may print 4 or 5
?>
Use of parentheses, even when not strictly necessary, can often increase readability of the code.

    Note:

    Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.

=====================================================================


Arithmetic Operators

Remember basic arithmetic from school? These work just like those.
Arithmetic Operators Example 	Name 	Result
-$a 	Negation 	Opposite of $a.
$a + $b 	Addition 	Sum of $a and $b.
$a - $b 	Subtraction 	Difference of $a and $b.
$a * $b 	Multiplication 	Product of $a and $b.
$a / $b 	Division 	Quotient of $a and $b.
$a % $b 	Modulus 	Remainder of $a divided by $b.

The division operator ("/") returns a float value unless the two operands are integers (or strings that get converted to integers) and the numbers are evenly divisible, in which case an integer value will be returned.

Operands of modulus are converted to integers (by stripping the decimal part) before processing.

The result of the modulus operator % has the same sign as the dividend — that is, the result of $a % $b will have the same sign as $a. For example:
<?php

echo (5 % 3)."\n";           // prints 2
echo (5 % -3)."\n";          // prints 2
echo (-5 % 3)."\n";          // prints -2
echo (-5 % -3)."\n";         // prints -2

?>

See also the manual page on Math functions.

=====================================================================


Assignment Operators

The basic assignment operator is "=". Your first inclination might be to think of this as "equal to". Don't. It really means that the left operand gets set to the value of the expression on the rights (that is, "gets set to").

The value of an assignment expression is the value assigned. That is, the value of "$a = 3" is 3. This allows you to do some tricky things:
<?php

$a = ($b = 4) + 5; // $a is equal to 9 now, and $b has been set to 4.

?>

For arrays, assigning a value to a named key is performed using the "=>" operator. The precedence of this operator is the same as other assignment operators.

In addition to the basic assignment operator, there are "combined operators" for all of the binary arithmetic, array union and string operators that allow you to use a value in an expression and then set its value to the result of that expression. For example:
<?php

$a = 3;
$a += 5; // sets $a to 8, as if we had said: $a = $a + 5;
$b = "Hello ";
$b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";

?>

Note that the assignment copies the original variable to the new one (assignment by value), so changes to one will not affect the other. This may also have relevance if you need to copy something like a large array inside a tight loop.

An exception to the usual assignment by value behaviour within PHP occurs with objects, which are assigned by reference in PHP 5. Objects may be explicitly copied via the clone keyword.
Assignment by Reference

Assignment by reference is also supported, using the "$var = &$othervar;" syntax. Assignment by reference means that both variables end up pointing at the same data, and nothing is copied anywhere.

Example #1 Assigning by reference
<?php
$a = 3;
$b = &$a; // $b is a reference to $a

print "$a\n"; // prints 3
print "$b\n"; // prints 3

$a = 4; // change $a

print "$a\n"; // prints 4
print "$b\n"; // prints 4 as well, since $b is a reference to $a, which has
              // been changed
?>

As of PHP 5, the new operator returns a reference automatically, so assigning the result of new by reference results in an E_DEPRECATED message in PHP 5.3 and later, and an E_STRICT message in earlier versions.

For example, this code will result in a warning:
<?php
class C {}

/* The following line generates the following error message:
 * Deprecated: Assigning the return value of new by reference is deprecated in...
 */
$o = &new C;
?>

More information on references and their potential uses can be found in the References Explained section of the manual.

=====================================================================


Bitwise Operators

Bitwise operators allow evaluation and manipulation of specific bits within an integer.
Bitwise Operators Example 	Name 	Result
$a & $b 	And 	Bits that are set in both $a and $b are set.
$a | $b 	Or (inclusive or) 	Bits that are set in either $a or $b are set.
$a ^ $b 	Xor (exclusive or) 	Bits that are set in $a or $b but not both are set.
~ $a 	Not 	Bits that are set in $a are not set, and vice versa.
$a << $b 	Shift left 	Shift the bits of $a $b steps to the left (each step means "multiply by two")
$a >> $b 	Shift right 	Shift the bits of $a $b steps to the right (each step means "divide by two")

Bit shifting in PHP is arithmetic. Bits shifted off either end are discarded. Left shifts have zeros shifted in on the right while the sign bit is shifted out on the left, meaning the sign of an operand is not preserved. Right shifts have copies of the sign bit shifted in on the left, meaning the sign of an operand is preserved.

Use parentheses to ensure the desired precedence. For example, $a & $b == true evaluates the equivalency then the bitwise and; while ($a & $b) == true evaluates the bitwise and then the equivalency.

Be aware of data type conversions. If both the left-hand and right-hand parameters are strings, the bitwise operator will operate on the characters' ASCII values.

PHP's error_reporting ini setting uses bitwise values,
providing a real-world demonstration of turning
bits off. To show all errors, except for notices,
the php.ini file instructions say to use:
E_ALL & ~E_NOTICE
      

This works by starting with E_ALL:
00000000000000000111011111111111
Then taking the value of E_NOTICE...
00000000000000000000000000001000
... and inverting it via ~:
11111111111111111111111111110111
Finally, it uses AND (&) to find the bits turned
on in both values:
00000000000000000111011111110111
      

Another way to accomplish that is using XOR (^)
to find bits that are on in only one value or the other:
E_ALL ^ E_NOTICE
      

error_reporting can also be used to demonstrate turning bits on.
The way to show just errors and recoverable errors is:
E_ERROR | E_RECOVERABLE_ERROR
      

This process combines E_ERROR
00000000000000000000000000000001
and
00000000000000000001000000000000
using the OR (|) operator
to get the bits turned on in either value:
00000000000000000001000000000001
      

Example #1 Bitwise AND, OR and XOR operations on integers
<?php
/*
 * Ignore the top section,
 * it is just formatting to make output clearer.
 */

$format = '(%1$2d = %1$04b) = (%2$2d = %2$04b)'
        . ' %3$s (%4$2d = %4$04b)' . "\n";

echo <<<EOH
 ---------     ---------  -- ---------
 result        value      op test
 ---------     ---------  -- ---------
EOH;


/*
 * Here are the examples.
 */

$values = array(0, 1, 2, 4, 8);
$test = 1 + 4;

echo "\n Bitwise AND \n";
foreach ($values as $value) {
    $result = $value & $test;
    printf($format, $result, $value, '&', $test);
}

echo "\n Bitwise Inclusive OR \n";
foreach ($values as $value) {
    $result = $value | $test;
    printf($format, $result, $value, '|', $test);
}

echo "\n Bitwise Exclusive OR (XOR) \n";
foreach ($values as $value) {
    $result = $value ^ $test;
    printf($format, $result, $value, '^', $test);
}
?>

The above example will output:

 ---------     ---------  -- ---------
 result        value      op test
 ---------     ---------  -- ---------
 Bitwise AND
( 0 = 0000) = ( 0 = 0000) & ( 5 = 0101)
( 1 = 0001) = ( 1 = 0001) & ( 5 = 0101)
( 0 = 0000) = ( 2 = 0010) & ( 5 = 0101)
( 4 = 0100) = ( 4 = 0100) & ( 5 = 0101)
( 0 = 0000) = ( 8 = 1000) & ( 5 = 0101)

 Bitwise Inclusive OR
( 5 = 0101) = ( 0 = 0000) | ( 5 = 0101)
( 5 = 0101) = ( 1 = 0001) | ( 5 = 0101)
( 7 = 0111) = ( 2 = 0010) | ( 5 = 0101)
( 5 = 0101) = ( 4 = 0100) | ( 5 = 0101)
(13 = 1101) = ( 8 = 1000) | ( 5 = 0101)

 Bitwise Exclusive OR (XOR)
( 5 = 0101) = ( 0 = 0000) ^ ( 5 = 0101)
( 4 = 0100) = ( 1 = 0001) ^ ( 5 = 0101)
( 7 = 0111) = ( 2 = 0010) ^ ( 5 = 0101)
( 1 = 0001) = ( 4 = 0100) ^ ( 5 = 0101)
(13 = 1101) = ( 8 = 1000) ^ ( 5 = 0101)

Example #2 Bitwise XOR operations on strings
<?php
echo 12 ^ 9; // Outputs '5'

echo "12" ^ "9"; // Outputs the Backspace character (ascii 8)
                 // ('1' (ascii 49)) ^ ('9' (ascii 57)) = #8

echo "hallo" ^ "hello"; // Outputs the ascii values #0 #4 #0 #0 #0
                        // 'a' ^ 'e' = #4

echo 2 ^ "3"; // Outputs 1
              // 2 ^ ((int)"3") == 1

echo "2" ^ 3; // Outputs 1
              // ((int)"2") ^ 3 == 1
?>

Example #3 Bit shifting on integers
<?php
/*
 * Here are the examples.
 */

echo "\n--- BIT SHIFT RIGHT ON POSITIVE INTEGERS ---\n";

$val = 4;
$places = 1;
$res = $val >> $places;
p($res, $val, '>>', $places, 'copy of sign bit shifted into left side');

$val = 4;
$places = 2;
$res = $val >> $places;
p($res, $val, '>>', $places);

$val = 4;
$places = 3;
$res = $val >> $places;
p($res, $val, '>>', $places, 'bits shift out right side');

$val = 4;
$places = 4;
$res = $val >> $places;
p($res, $val, '>>', $places, 'same result as above; can not shift beyond 0');


echo "\n--- BIT SHIFT RIGHT ON NEGATIVE INTEGERS ---\n";

$val = -4;
$places = 1;
$res = $val >> $places;
p($res, $val, '>>', $places, 'copy of sign bit shifted into left side');

$val = -4;
$places = 2;
$res = $val >> $places;
p($res, $val, '>>', $places, 'bits shift out right side');

$val = -4;
$places = 3;
$res = $val >> $places;
p($res, $val, '>>', $places, 'same result as above; can not shift beyond -1');


echo "\n--- BIT SHIFT LEFT ON POSITIVE INTEGERS ---\n";

$val = 4;
$places = 1;
$res = $val << $places;
p($res, $val, '<<', $places, 'zeros fill in right side');

$val = 4;
$places = (PHP_INT_SIZE * 8) - 4;
$res = $val << $places;
p($res, $val, '<<', $places);

$val = 4;
$places = (PHP_INT_SIZE * 8) - 3;
$res = $val << $places;
p($res, $val, '<<', $places, 'sign bits get shifted out');

$val = 4;
$places = (PHP_INT_SIZE * 8) - 2;
$res = $val << $places;
p($res, $val, '<<', $places, 'bits shift out left side');


echo "\n--- BIT SHIFT LEFT ON NEGATIVE INTEGERS ---\n";

$val = -4;
$places = 1;
$res = $val << $places;
p($res, $val, '<<', $places, 'zeros fill in right side');

$val = -4;
$places = (PHP_INT_SIZE * 8) - 3;
$res = $val << $places;
p($res, $val, '<<', $places);

$val = -4;
$places = (PHP_INT_SIZE * 8) - 2;
$res = $val << $places;
p($res, $val, '<<', $places, 'bits shift out left side, including sign bit');


/*
 * Ignore this bottom section,
 * it is just formatting to make output clearer.
 */

function p($res, $val, $op, $places, $note = '') {
    $format = '%0' . (PHP_INT_SIZE * 8) . "b\n";

    printf("Expression: %d = %d %s %d\n", $res, $val, $op, $places);

    echo " Decimal:\n";
    printf("  val=%d\n", $val);
    printf("  res=%d\n", $res);

    echo " Binary:\n";
    printf('  val=' . $format, $val);
    printf('  res=' . $format, $res);

    if ($note) {
        echo " NOTE: $note\n";
    }

    echo "\n";
}
?>

Output of the above example on 32 bit machines:

--- BIT SHIFT RIGHT ON POSITIVE INTEGERS ---
Expression: 2 = 4 >> 1
 Decimal:
  val=4
  res=2
 Binary:
  val=00000000000000000000000000000100
  res=00000000000000000000000000000010
 NOTE: copy of sign bit shifted into left side

Expression: 1 = 4 >> 2
 Decimal:
  val=4
  res=1
 Binary:
  val=00000000000000000000000000000100
  res=00000000000000000000000000000001

Expression: 0 = 4 >> 3
 Decimal:
  val=4
  res=0
 Binary:
  val=00000000000000000000000000000100
  res=00000000000000000000000000000000
 NOTE: bits shift out right side

Expression: 0 = 4 >> 4
 Decimal:
  val=4
  res=0
 Binary:
  val=00000000000000000000000000000100
  res=00000000000000000000000000000000
 NOTE: same result as above; can not shift beyond 0


--- BIT SHIFT RIGHT ON NEGATIVE INTEGERS ---
Expression: -2 = -4 >> 1
 Decimal:
  val=-4
  res=-2
 Binary:
  val=11111111111111111111111111111100
  res=11111111111111111111111111111110
 NOTE: copy of sign bit shifted into left side

Expression: -1 = -4 >> 2
 Decimal:
  val=-4
  res=-1
 Binary:
  val=11111111111111111111111111111100
  res=11111111111111111111111111111111
 NOTE: bits shift out right side

Expression: -1 = -4 >> 3
 Decimal:
  val=-4
  res=-1
 Binary:
  val=11111111111111111111111111111100
  res=11111111111111111111111111111111
 NOTE: same result as above; can not shift beyond -1


--- BIT SHIFT LEFT ON POSITIVE INTEGERS ---
Expression: 8 = 4 << 1
 Decimal:
  val=4
  res=8
 Binary:
  val=00000000000000000000000000000100
  res=00000000000000000000000000001000
 NOTE: zeros fill in right side

Expression: 1073741824 = 4 << 28
 Decimal:
  val=4
  res=1073741824
 Binary:
  val=00000000000000000000000000000100
  res=01000000000000000000000000000000

Expression: -2147483648 = 4 << 29
 Decimal:
  val=4
  res=-2147483648
 Binary:
  val=00000000000000000000000000000100
  res=10000000000000000000000000000000
 NOTE: sign bits get shifted out

Expression: 0 = 4 << 30
 Decimal:
  val=4
  res=0
 Binary:
  val=00000000000000000000000000000100
  res=00000000000000000000000000000000
 NOTE: bits shift out left side


--- BIT SHIFT LEFT ON NEGATIVE INTEGERS ---
Expression: -8 = -4 << 1
 Decimal:
  val=-4
  res=-8
 Binary:
  val=11111111111111111111111111111100
  res=11111111111111111111111111111000
 NOTE: zeros fill in right side

Expression: -2147483648 = -4 << 29
 Decimal:
  val=-4
  res=-2147483648
 Binary:
  val=11111111111111111111111111111100
  res=10000000000000000000000000000000

Expression: 0 = -4 << 30
 Decimal:
  val=-4
  res=0
 Binary:
  val=11111111111111111111111111111100
  res=00000000000000000000000000000000
 NOTE: bits shift out left side, including sign bit

Output of the above example on 64 bit machines:

--- BIT SHIFT RIGHT ON POSITIVE INTEGERS ---
Expression: 2 = 4 >> 1
 Decimal:
  val=4
  res=2
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0000000000000000000000000000000000000000000000000000000000000010
 NOTE: copy of sign bit shifted into left side

Expression: 1 = 4 >> 2
 Decimal:
  val=4
  res=1
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0000000000000000000000000000000000000000000000000000000000000001

Expression: 0 = 4 >> 3
 Decimal:
  val=4
  res=0
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0000000000000000000000000000000000000000000000000000000000000000
 NOTE: bits shift out right side

Expression: 0 = 4 >> 4
 Decimal:
  val=4
  res=0
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0000000000000000000000000000000000000000000000000000000000000000
 NOTE: same result as above; can not shift beyond 0


--- BIT SHIFT RIGHT ON NEGATIVE INTEGERS ---
Expression: -2 = -4 >> 1
 Decimal:
  val=-4
  res=-2
 Binary:
  val=1111111111111111111111111111111111111111111111111111111111111100
  res=1111111111111111111111111111111111111111111111111111111111111110
 NOTE: copy of sign bit shifted into left side

Expression: -1 = -4 >> 2
 Decimal:
  val=-4
  res=-1
 Binary:
  val=1111111111111111111111111111111111111111111111111111111111111100
  res=1111111111111111111111111111111111111111111111111111111111111111
 NOTE: bits shift out right side

Expression: -1 = -4 >> 3
 Decimal:
  val=-4
  res=-1
 Binary:
  val=1111111111111111111111111111111111111111111111111111111111111100
  res=1111111111111111111111111111111111111111111111111111111111111111
 NOTE: same result as above; can not shift beyond -1


--- BIT SHIFT LEFT ON POSITIVE INTEGERS ---
Expression: 8 = 4 << 1
 Decimal:
  val=4
  res=8
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0000000000000000000000000000000000000000000000000000000000001000
 NOTE: zeros fill in right side

Expression: 4611686018427387904 = 4 << 60
 Decimal:
  val=4
  res=4611686018427387904
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0100000000000000000000000000000000000000000000000000000000000000

Expression: -9223372036854775808 = 4 << 61
 Decimal:
  val=4
  res=-9223372036854775808
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=1000000000000000000000000000000000000000000000000000000000000000
 NOTE: sign bits get shifted out

Expression: 0 = 4 << 62
 Decimal:
  val=4
  res=0
 Binary:
  val=0000000000000000000000000000000000000000000000000000000000000100
  res=0000000000000000000000000000000000000000000000000000000000000000
 NOTE: bits shift out left side


--- BIT SHIFT LEFT ON NEGATIVE INTEGERS ---
Expression: -8 = -4 << 1
 Decimal:
  val=-4
  res=-8
 Binary:
  val=1111111111111111111111111111111111111111111111111111111111111100
  res=1111111111111111111111111111111111111111111111111111111111111000
 NOTE: zeros fill in right side

Expression: -9223372036854775808 = -4 << 61
 Decimal:
  val=-4
  res=-9223372036854775808
 Binary:
  val=1111111111111111111111111111111111111111111111111111111111111100
  res=1000000000000000000000000000000000000000000000000000000000000000

Expression: 0 = -4 << 62
 Decimal:
  val=-4
  res=0
 Binary:
  val=1111111111111111111111111111111111111111111111111111111111111100
  res=0000000000000000000000000000000000000000000000000000000000000000
 NOTE: bits shift out left side, including sign bit

Warning

Don't right shift for more than 32 bits on 32 bits systems. Don't left shift in case it results to number longer than 32 bits. Use functions from the gmp extension for bitwise manipulation on numbers beyond PHP_INT_MAX.

See also pack(), unpack(), gmp_and(), gmp_or(), gmp_xor(), gmp_testbit(), gmp_clrbit()

=====================================================================


Comparison Operators

Comparison operators, as their name implies, allow you to compare two values. You may also be interested in viewing the type comparison tables, as they show examples of various type related comparisons.
Comparison Operators Example 	Name 	Result
$a == $b 	Equal 	TRUE if $a is equal to $b after type juggling.
$a === $b 	Identical 	TRUE if $a is equal to $b, and they are of the same type. (introduced in PHP 4)
$a != $b 	Not equal 	TRUE if $a is not equal to $b after type juggling.
$a <> $b 	Not equal 	TRUE if $a is not equal to $b after type juggling.
$a !== $b 	Not identical 	TRUE if $a is not equal to $b, or they are not of the same type. (introduced in PHP 4)
$a < $b 	Less than 	TRUE if $a is strictly less than $b.
$a > $b 	Greater than 	TRUE if $a is strictly greater than $b.
$a <= $b 	Less than or equal to 	TRUE if $a is less than or equal to $b.
$a >= $b 	Greater than or equal to 	TRUE if $a is greater than or equal to $b.

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. These rules also apply to the switch statement. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.
<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true

switch ("a") {
case 0:
    echo "0";
    break;
case "a": // never reached because "a" is already matched with 0
    echo "a";
    break;
}
?>

For various types, comparison is done according to the following table (in order).
Comparison with Various Types Type of Operand 1 	Type of Operand 2 	Result
null or string 	string 	Convert NULL to "", numerical or lexical comparison
bool or null 	anything 	Convert to bool, FALSE < TRUE
object 	object 	Built-in classes can define its own comparison, different classes are uncomparable, same class - compare properties the same way as arrays (PHP 4), PHP 5 has its own explanation
string, resource or number 	string, resource or number 	Translate strings and resources to numbers, usual math
array 	array 	Array with fewer members is smaller, if key from operand 1 is not found in operand 2 then arrays are uncomparable, otherwise - compare value by value (see following example)
array 	anything 	array is always greater
object 	anything 	object is always greater

Example #1 Transcription of standard array comparison
<?php
// Arrays are compared like this with standard comparison operators
function standard_array_compare($op1, $op2)
{
    if (count($op1) < count($op2)) {
        return -1; // $op1 < $op2
    } elseif (count($op1) > count($op2)) {
        return 1; // $op1 > $op2
    }
    foreach ($op1 as $key => $val) {
        if (!array_key_exists($key, $op2)) {
            return null; // uncomparable
        } elseif ($val < $op2[$key]) {
            return -1;
        } elseif ($val > $op2[$key]) {
            return 1;
        }
    }
    return 0; // $op1 == $op2
}
?>

See also strcasecmp(), strcmp(), Array operators, and the manual section on Types.
Warning
Comparison of floating point numbers

Because of the way floats are represented internally, you should not test two floats for equality.

See the documentation for float for more information.
Ternary Operator

Another conditional operator is the "?:" (or ternary) operator.

Example #2 Assigning a default value
<?php
// Example usage for: Ternary Operator
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

// The above is identical to this if/else statement
if (empty($_POST['action'])) {
    $action = 'default';
} else {
    $action = $_POST['action'];
}

?>
The expression (expr1) ? (expr2) : (expr3) evaluates to expr2 if expr1 evaluates to TRUE, and expr3 if expr1 evaluates to FALSE.

Since PHP 5.3, it is possible to leave out the middle part of the ternary operator. Expression expr1 ?: expr3 returns expr1 if expr1 evaluates to TRUE, and expr3 otherwise.

    Note: Please note that the ternary operator is a statement, and that it doesn't evaluate to a variable, but to the result of a statement. This is important to know if you want to return a variable by reference. The statement return $var == 42 ? $a : $b; in a return-by-reference function will therefore not work and a warning is issued in later PHP versions. 

    Note:

    It is recommended that you avoid "stacking" ternary expressions. PHP's behaviour when using more than one ternary operator within a single statement is non-obvious:

    Example #3 Non-obvious Ternary Behaviour
    <?php
    // on first glance, the following appears to output 'true'
    echo (true?'true':false?'t':'f');

    // however, the actual output of the above is 't'
    // this is because ternary expressions are evaluated from left to right

    // the following is a more obvious version of the same code as above
    echo ((true ? 'true' : false) ? 't' : 'f');

    // here, you can see that the first expression is evaluated to 'true', which
    // in turn evaluates to (bool)true, thus returning the true branch of the
    // second ternary expression.
    ?>

=====================================================================


Error Control Operators

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

If the track_errors feature is enabled, any error message generated by the expression will be saved in the variable $php_errormsg. This variable will be overwritten on each error, so check early if you want to use it.

<?php
/* Intentional file error */
$my_file = @file ('non_existent_file') or
    die ("Failed opening file: error was '$php_errormsg'");

// this works for any expression, not just functions:
$value = @$cache[$key];
// will not issue a notice if the index $key doesn't exist.

?>

    Note: The @-operator works only on expressions. A simple rule of thumb is: if you can take the value of something, you can prepend the @ operator to it. For instance, you can prepend it to variables, function and include() calls, constants, and so forth. You cannot prepend it to function or class definitions, or conditional structures such as if and foreach, and so forth. 

See also error_reporting() and the manual section for Error Handling and Logging functions.
Warning

Currently the "@" error-control operator prefix will even disable error reporting for critical errors that will terminate script execution. Among other things, this means that if you use "@" to suppress errors from a certain function and either it isn't available or has been mistyped, the script will die right there with no indication as to why.

=====================================================================


Execution Operators

PHP supports one execution operator: backticks (``). Note that these are not single-quotes! PHP will attempt to execute the contents of the backticks as a shell command; the output will be returned (i.e., it won't simply be dumped to output; it can be assigned to a variable). Use of the backtick operator is identical to shell_exec().
<?php
$output = `ls -al`;
echo "<pre>$output</pre>";
?>

    Note:

    The backtick operator is disabled when safe mode is enabled or shell_exec() is disabled.

See also the manual section on Program Execution functions, popen() proc_open(), and Using PHP from the commandline.

=====================================================================


Incrementing/Decrementing Operators

PHP supports C-style pre- and post-increment and decrement operators.

    Note: The increment/decrement operators do not affect boolean values. Decrementing NULL values has no effect too, but incrementing them results in 1. 

Increment/decrement Operators Example 	Name 	Effect
++$a 	Pre-increment 	Increments $a by one, then returns $a.
$a++ 	Post-increment 	Returns $a, then increments $a by one.
--$a 	Pre-decrement 	Decrements $a by one, then returns $a.
$a-- 	Post-decrement 	Returns $a, then decrements $a by one.

Here's a simple example script:
<?php
echo "<h3>Postincrement</h3>";
$a = 5;
echo "Should be 5: " . $a++ . "<br />\n";
echo "Should be 6: " . $a . "<br />\n";

echo "<h3>Preincrement</h3>";
$a = 5;
echo "Should be 6: " . ++$a . "<br />\n";
echo "Should be 6: " . $a . "<br />\n";

echo "<h3>Postdecrement</h3>";
$a = 5;
echo "Should be 5: " . $a-- . "<br />\n";
echo "Should be 4: " . $a . "<br />\n";

echo "<h3>Predecrement</h3>";
$a = 5;
echo "Should be 4: " . --$a . "<br />\n";
echo "Should be 4: " . $a . "<br />\n";
?>

PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in PHP and Perl $a = 'Z'; $a++; turns $a into 'AA', while in C a = 'Z'; a++; turns a into '[' (ASCII value of 'Z' is 90, ASCII value of '[' is 91). Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported. Incrementing/decrementing other character variables has no effect, the original string is unchanged.

Example #1 Arithmetic Operations on Character Variables
<?php
$i = 'W';
for ($n=0; $n<6; $n++) {
    echo ++$i . "\n";
}
?>

The above example will output:

X
Y
Z
AA
AB
AC

Incrementing or decrementing booleans has no effect.

=====================================================================


Logical Operators
Logical Operators Example 	Name 	Result
$a and $b 	And 	TRUE if both $a and $b are TRUE.
$a or $b 	Or 	TRUE if either $a or $b is TRUE.
$a xor $b 	Xor 	TRUE if either $a or $b is TRUE, but not both.
! $a 	Not 	TRUE if $a is not TRUE.
$a && $b 	And 	TRUE if both $a and $b are TRUE.
$a || $b 	Or 	TRUE if either $a or $b is TRUE.

The reason for the two different variations of "and" and "or" operators is that they operate at different precedences. (See Operator Precedence.)

Example #1 Logical operators illustrated
<?php

// --------------------
// foo() will never get called as those operators are short-circuit

$a = (false && foo());
$b = (true  || foo());
$c = (false and foo());
$d = (true  or  foo());

// --------------------
// "||" has a greater precedence than "or"

// The result of the expression (false || true) is assigned to $e
// Acts like: ($e = (false || true))
$e = false || true;

// The constant false is assigned to $f and then true is ignored
// Acts like: (($f = false) or true)
$f = false or true;

var_dump($e, $f);

// --------------------
// "&&" has a greater precedence than "and"

// The result of the expression (true && false) is assigned to $g
// Acts like: ($g = (true && false))
$g = true && false;

// The constant true is assigned to $h and then false is ignored
// Acts like: (($h = true) and false)
$h = true and false;

var_dump($g, $h);
?>

The above example will output something similar to:

bool(true)
bool(false)
bool(false)
bool(true)

=====================================================================


String Operators

There are two string operators. The first is the concatenation operator ('.'), which returns the concatenation of its right and left arguments. The second is the concatenating assignment operator ('.='), which appends the argument on the right side to the argument on the left side. Please read Assignment Operators for more information.

<?php
$a = "Hello ";
$b = $a . "World!"; // now $b contains "Hello World!"

$a = "Hello ";
$a .= "World!";     // now $a contains "Hello World!"
?>

See also the manual sections on the String type and String functions.

=====================================================================


Array Operators
Array Operators Example 	Name 	Result
$a + $b 	Union 	Union of $a and $b.
$a == $b 	Equality 	TRUE if $a and $b have the same key/value pairs.
$a === $b 	Identity 	TRUE if $a and $b have the same key/value pairs in the same order and of the same types.
$a != $b 	Inequality 	TRUE if $a is not equal to $b.
$a <> $b 	Inequality 	TRUE if $a is not equal to $b.
$a !== $b 	Non-identity 	TRUE if $a is not identical to $b.

The + operator returns the right-hand array appended to the left-hand array; for keys that exist in both arrays, the elements from the left-hand array will be used, and the matching elements from the right-hand array will be ignored.

<?php
$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");

$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
var_dump($c);

$c = $b + $a; // Union of $b and $a
echo "Union of \$b and \$a: \n";
var_dump($c);
?>
When executed, this script will print the following:

Union of $a and $b:
array(3) {
  ["a"]=>
  string(5) "apple"
  ["b"]=>
  string(6) "banana"
  ["c"]=>
  string(6) "cherry"
}
Union of $b and $a:
array(3) {
  ["a"]=>
  string(4) "pear"
  ["b"]=>
  string(10) "strawberry"
  ["c"]=>
  string(6) "cherry"
}

Elements of arrays are equal for the comparison if they have the same key and value.

Example #1 Comparing arrays
<?php
$a = array("apple", "banana");
$b = array(1 => "banana", "0" => "apple");

var_dump($a == $b); // bool(true)
var_dump($a === $b); // bool(false)
?>

See also the manual sections on the Array type and Array functions.

=====================================================================


Type Operators

instanceof is used to determine whether a PHP variable is an instantiated object of a certain class:

Example #1 Using instanceof with classes
<?php
class MyClass
{
}

class NotMyClass
{
}
$a = new MyClass;

var_dump($a instanceof MyClass);
var_dump($a instanceof NotMyClass);
?>

The above example will output:

bool(true)
bool(false)

instanceof can also be used to determine whether a variable is an instantiated object of a class that inherits from a parent class:

Example #2 Using instanceof with inherited classes
<?php
class ParentClass
{
}

class MyClass extends ParentClass
{
}

$a = new MyClass;

var_dump($a instanceof MyClass);
var_dump($a instanceof ParentClass);
?>

The above example will output:

bool(true)
bool(true)

To check if an object is not an instanceof a class, the logical not operator can be used.

Example #3 Using instanceof to check if object is not an instanceof a class
<?php
class MyClass
{
}

$a = new MyClass;
var_dump(!($a instanceof stdClass));
?>

The above example will output:

bool(true)

Lastly, instanceof can also be used to determine whether a variable is an instantiated object of a class that implements an interface:

Example #4 Using instanceof for class
<?php
interface MyInterface
{
}

class MyClass implements MyInterface
{
}

$a = new MyClass;

var_dump($a instanceof MyClass);
var_dump($a instanceof MyInterface);
?>

The above example will output:

bool(true)
bool(true)

Although instanceof is usually used with a literal classname, it can also be used with another object or a string variable:

Example #5 Using instanceof with other variables
<?php
interface MyInterface
{
}

class MyClass implements MyInterface
{
}

$a = new MyClass;
$b = new MyClass;
$c = 'MyClass';
$d = 'NotMyClass';

var_dump($a instanceof $b); // $b is an object of class MyClass
var_dump($a instanceof $c); // $c is a string 'MyClass'
var_dump($a instanceof $d); // $d is a string 'NotMyClass'
?>

The above example will output:

bool(true)
bool(true)
bool(false)

There are a few pitfalls to be aware of. Before PHP version 5.1.0, instanceof would call __autoload() if the class name did not exist. In addition, if the class was not loaded, a fatal error would occur. This can be worked around by using a dynamic class reference, or a string variable containing the class name:

Example #6 Avoiding classname lookups and fatal errors with instanceof in PHP 5.0
<?php
$d = 'NotMyClass';
var_dump($a instanceof $d); // no fatal error here
?>

The above example will output:

bool(false)

The instanceof operator was introduced in PHP 5. Before this time is_a() was used but is_a() has since been deprecated in favor of instanceof. Note that as of PHP 5.3.0, is_a() is no longer deprecated.

See also get_class() and is_a().

=====================================================================
=====================================================================
    * Control Structures
=====================================================================

Table of Contents

    * Introduction
    * if
    * else
    * elseif/else if
    * Alternative syntax for control structures
    * while
    * do-while
    * for
    * foreach
    * break
    * continue
    * switch
    * declare
    * return
    * require
    * include
    * require_once
    * include_once
    * goto

=====================================================================

Introduction

Any PHP script is built out of a series of statements. A statement can be an assignment, a function call, a loop, a conditional statement or even a statement that does nothing (an empty statement). Statements usually end with a semicolon. In addition, statements can be grouped into a statement-group by encapsulating a group of statements with curly braces. A statement-group is a statement by itself as well. The various statement types are described in this chapter.

=====================================================================


if

The if construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an if structure that is similar to that of C:

if (expr)
  statement

As described in the section about expressions, expression is evaluated to its Boolean value. If expression evaluates to TRUE, PHP will execute statement, and if it evaluates to FALSE - it'll ignore it. More information about what values evaluate to FALSE can be found in the 'Converting to boolean' section.

The following example would display a is bigger than b if $a is bigger than $b:
<?php
if ($a > $b)
  echo "a is bigger than b";
?>

Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an if clause. Instead, you can group several statements into a statement group. For example, this code would display a is bigger than b if $a is bigger than $b, and would then assign the value of $a into $b:
<?php
if ($a > $b) {
  echo "a is bigger than b";
  $b = $a;
}
?>

If statements can be nested infinitely within other if statements, which provides you with complete flexibility for conditional execution of the various parts of your program.

=====================================================================

else

Often you'd want to execute a statement if a certain condition is met, and a different statement if the condition is not met. This is what else is for. else extends an if statement to execute a statement in case the expression in the if statement evaluates to FALSE. For example, the following code would display a is greater than b if $a is greater than $b, and a is NOT greater than b otherwise:
<?php
if ($a > $b) {
  echo "a is greater than b";
} else {
  echo "a is NOT greater than b";
}
?>
The else statement is only executed if the if expression evaluated to FALSE, and if there were any elseif expressions - only if they evaluated to FALSE as well (see elseif). 

=====================================================================


elseif/else if

elseif, as its name suggests, is a combination of if and else. Like else, it extends an if statement to execute a different statement in case the original if expression evaluates to FALSE. However, unlike else, it will execute that alternative expression only if the elseif conditional expression evaluates to TRUE. For example, the following code would display a is bigger than b, a equal to b or a is smaller than b:
<?php
if ($a > $b) {
    echo "a is bigger than b";
} elseif ($a == $b) {
    echo "a is equal to b";
} else {
    echo "a is smaller than b";
}
?>

There may be several elseifs within the same if statement. The first elseif expression (if any) that evaluates to TRUE would be executed. In PHP, you can also write 'else if' (in two words) and the behavior would be identical to the one of 'elseif' (in a single word). The syntactic meaning is slightly different (if you're familiar with C, this is the same behavior) but the bottom line is that both would result in exactly the same behavior.

The elseif statement is only executed if the preceding if expression and any preceding elseif expressions evaluated to FALSE, and the current elseif expression evaluated to TRUE.

    Note: Note that elseif and else if will only be considered exactly the same when using curly brackets as in the above example. When using a colon to define your if/elseif conditions, you must not separate else if into two words, or PHP will fail with a parse error. 

<?php

/* Incorrect Method: */
if($a > $b):
    echo $a." is greater than ".$b;
else if($a == $b): // Will not compile.
    echo "The above line causes a parse error.";
endif;


/* Correct Method: */
if($a > $b):
    echo $a." is greater than ".$b;
elseif($a == $b): // Note the combination of the words.
    echo $a." equals ".$b;
else:
    echo $a." is neither greater than or equal to ".$b;
endif;

?>

=====================================================================


Alternative syntax for control structures

PHP offers an alternative syntax for some of its control structures; namely, if, while, for, foreach, and switch. In each case, the basic form of the alternate syntax is to change the opening brace to a colon (:) and the closing brace to endif;, endwhile;, endfor;, endforeach;, or endswitch;, respectively.
<?php if ($a == 5): ?>
A is equal to 5
<?php endif; ?>

In the above example, the HTML block "A is equal to 5" is nested within an if statement written in the alternative syntax. The HTML block would be displayed only if $a is equal to 5.

The alternative syntax applies to else and elseif as well. The following is an if structure with elseif and else in the alternative format:
<?php
if ($a == 5):
    echo "a equals 5";
    echo "...";
elseif ($a == 6):
    echo "a equals 6";
    echo "!!!";
else:
    echo "a is neither 5 nor 6";
endif;
?>

    Note:

    Mixing syntaxes in the same control block is not supported.

See also while, for, and if for further examples.

=====================================================================


while

while loops are the simplest type of loop in PHP. They behave just like their C counterparts. The basic form of a while statement is:

while (expr)
    statement

The meaning of a while statement is simple. It tells PHP to execute the nested statement(s) repeatedly, as long as the while expression evaluates to TRUE. The value of the expression is checked each time at the beginning of the loop, so even if this value changes during the execution of the nested statement(s), execution will not stop until the end of the iteration (each time PHP runs the statements in the loop is one iteration). Sometimes, if the while expression evaluates to FALSE from the very beginning, the nested statement(s) won't even be run once.

Like with the if statement, you can group multiple statements within the same while loop by surrounding a group of statements with curly braces, or by using the alternate syntax:

while (expr):
    statement
    ...
endwhile;

The following examples are identical, and both print the numbers 1 through 10:
<?php
/* example 1 */

$i = 1;
while ($i <= 10) {
    echo $i++;  /* the printed value would be
                   $i before the increment
                   (post-increment) */
}

/* example 2 */

$i = 1;
while ($i <= 10):
    echo $i;
    $i++;
endwhile;
?>

=====================================================================


do-while

do-while loops are very similar to while loops, except the truth expression is checked at the end of each iteration instead of in the beginning. The main difference from regular while loops is that the first iteration of a do-while loop is guaranteed to run (the truth expression is only checked at the end of the iteration), whereas it may not necessarily run with a regular while loop (the truth expression is checked at the beginning of each iteration, if it evaluates to FALSE right from the beginning, the loop execution would end immediately).

There is just one syntax for do-while loops:
<?php
$i = 0;
do {
    echo $i;
} while ($i > 0);
?>

The above loop would run one time exactly, since after the first iteration, when truth expression is checked, it evaluates to FALSE ($i is not bigger than 0) and the loop execution ends.

Advanced C users may be familiar with a different usage of the do-while loop, to allow stopping execution in the middle of code blocks, by encapsulating them with do-while (0), and using the break statement. The following code fragment demonstrates this:
<?php
do {
    if ($i < 5) {
        echo "i is not big enough";
        break;
    }
    $i *= $factor;
    if ($i < $minimum_limit) {
        break;
    }
   echo "i is ok";

    /* process i */

} while (0);
?>

Don't worry if you don't understand this right away or at all. You can code scripts and even powerful scripts without using this 'feature'. Since PHP 5.3.0, it is possible to use goto operator instead of this hack.

=====================================================================


for

for loops are the most complex loops in PHP. They behave like their C counterparts. The syntax of a for loop is:

for (expr1; expr2; expr3)
    statement

The first expression (expr1) is evaluated (executed) once unconditionally at the beginning of the loop.

In the beginning of each iteration, expr2 is evaluated. If it evaluates to TRUE, the loop continues and the nested statement(s) are executed. If it evaluates to FALSE, the execution of the loop ends.

At the end of each iteration, expr3 is evaluated (executed).

Each of the expressions can be empty or contain multiple expressions separated by commas. In expr2, all expressions separated by a comma are evaluated but the result is taken from the last part. expr2 being empty means the loop should be run indefinitely (PHP implicitly considers it as TRUE, like C). This may not be as useless as you might think, since often you'd want to end the loop using a conditional break statement instead of using the for truth expression.

Consider the following examples. All of them display the numbers 1 through 10:
<?php
/* example 1 */

for ($i = 1; $i <= 10; $i++) {
    echo $i;
}

/* example 2 */

for ($i = 1; ; $i++) {
    if ($i > 10) {
        break;
    }
    echo $i;
}

/* example 3 */

$i = 1;
for (; ; ) {
    if ($i > 10) {
        break;
    }
    echo $i;
    $i++;
}

/* example 4 */

for ($i = 1, $j = 0; $i <= 10; $j += $i, print $i, $i++);
?>

Of course, the first example appears to be the nicest one (or perhaps the fourth), but you may find that being able to use empty expressions in for loops comes in handy in many occasions.

PHP also supports the alternate "colon syntax" for for loops.

for (expr1; expr2; expr3):
    statement
    ...
endfor;

Its a common thing to many users to iterate though arrays like in the example below.

<?php
/*
* This is an array with some data we want to modify
* when running through the for loop.
*/
$people = Array(
        Array('name' => 'Kalle', 'salt' => 856412),
        Array('name' => 'Pierre', 'salt' => 215863)
        );

for($i = 0; $i < sizeof($people); ++$i)
{
    $people[$i]['salt'] = rand(000000, 999999);
}
?>

The problem lies in the second for expression. This code can be slow because it has to calculate the size of the array on each iteration. Since the size never change, it can be optimized easily using an intermediate variable to store the size and use in the loop instead of sizeof. The example below illustrates this:

<?php
$people = Array(
        Array('name' => 'Kalle', 'salt' => 856412),
        Array('name' => 'Pierre', 'salt' => 215863)
        );

for($i = 0, $size = sizeof($people); $i < $size; ++$i)
{
    $people[$i]['salt'] = rand(000000, 999999);
}
?>

=====================================================================


foreach

PHP 4 introduced a foreach construct, much like Perl and some other languages. This simply gives an easy way to iterate over arrays. foreach works only on arrays, and will issue an error when you try to use it on a variable with a different data type or an uninitialized variable. There are two syntaxes; the second is a minor but useful extension of the first:

foreach (array_expression as $value)
    statement
foreach (array_expression as $key => $value)
    statement

The first form loops over the array given by array_expression. On each loop, the value of the current element is assigned to $value and the internal array pointer is advanced by one (so on the next loop, you'll be looking at the next element).

The second form does the same thing, except that the current element's key will be assigned to the variable $key on each loop.

As of PHP 5, it is possible to iterate objects too.

    Note:

    When foreach first starts executing, the internal array pointer is automatically reset to the first element of the array. This means that you do not need to call reset() before a foreach loop.

    Note:

    Unless the array is referenced, foreach operates on a copy of the specified array and not the array itself. foreach has some side effects on the array pointer. Don't rely on the array pointer during or after the foreach without resetting it.

As of PHP 5, you can easily modify array's elements by preceding $value with &. This will assign reference instead of copying the value.
<?php
$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
    $value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
unset($value); // break the reference with the last element
?>
This is possible only if iterated array can be referenced (i.e. is variable), that means the following code won't work:
<?php
foreach (array(1, 2, 3, 4) as &$value) {
    $value = $value * 2;
}

?>
Warning

Reference of a $value and the last array element remain even after the foreach loop. It is recommended to destroy it by unset().

    Note:

    foreach does not support the ability to suppress error messages using '@'.

You may have noticed that the following are functionally identical:
<?php
$arr = array("one", "two", "three");
reset($arr);
while (list(, $value) = each($arr)) {
    echo "Value: $value<br />\n";
}

foreach ($arr as $value) {
    echo "Value: $value<br />\n";
}
?>
The following are also functionally identical:
<?php
$arr = array("one", "two", "three");
reset($arr);
while (list($key, $value) = each($arr)) {
    echo "Key: $key; Value: $value<br />\n";
}

foreach ($arr as $key => $value) {
    echo "Key: $key; Value: $value<br />\n";
}
?>

Some more examples to demonstrate usages:
<?php
/* foreach example 1: value only */

$a = array(1, 2, 3, 17);

foreach ($a as $v) {
    echo "Current value of \$a: $v.\n";
}

/* foreach example 2: value (with its manual access notation printed for illustration) */

$a = array(1, 2, 3, 17);

$i = 0; /* for illustrative purposes only */

foreach ($a as $v) {
    echo "\$a[$i] => $v.\n";
    $i++;
}

/* foreach example 3: key and value */

$a = array(
    "one" => 1,
    "two" => 2,
    "three" => 3,
    "seventeen" => 17
);

foreach ($a as $k => $v) {
    echo "\$a[$k] => $v.\n";
}

/* foreach example 4: multi-dimensional arrays */
$a = array();
$a[0][0] = "a";
$a[0][1] = "b";
$a[1][0] = "y";
$a[1][1] = "z";

foreach ($a as $v1) {
    foreach ($v1 as $v2) {
        echo "$v2\n";
    }
}

/* foreach example 5: dynamic arrays */

foreach (array(1, 2, 3, 4, 5) as $v) {
    echo "$v\n";
}
?>

=====================================================================


break

break ends execution of the current for, foreach, while, do-while or switch structure.

break accepts an optional numeric argument which tells it how many nested enclosing structures are to be broken out of.

<?php
$arr = array('one', 'two', 'three', 'four', 'stop', 'five');
while (list(, $val) = each($arr)) {
    if ($val == 'stop') {
        break;    /* You could also write 'break 1;' here. */
    }
    echo "$val<br />\n";
}

/* Using the optional argument. */

$i = 0;
while (++$i) {
    switch ($i) {
    case 5:
        echo "At 5<br />\n";
        break 1;  /* Exit only the switch. */
    case 10:
        echo "At 10; quitting<br />\n";
        break 2;  /* Exit the switch and the while. */
    default:
        break;
    }
}
?>

=====================================================================


continue

continue is used within looping structures to skip the rest of the current loop iteration and continue execution at the condition evaluation and then the beginning of the next iteration.

    Note: Note that in PHP the switch statement is considered a looping structure for the purposes of continue. 

continue accepts an optional numeric argument which tells it how many levels of enclosing loops it should skip to the end of.

    Note:

    continue 0; and continue 1; is the same as running continue;.

<?php
while (list($key, $value) = each($arr)) {
    if (!($key % 2)) { // skip odd members
        continue;
    }
    do_something_odd($value);
}

$i = 0;
while ($i++ < 5) {
    echo "Outer<br />\n";
    while (1) {
        echo "&nbsp;Middle<br />\n";
        while (1) {
            echo "&nbsp;&nbsp;Inner<br />\n";
            continue 3;
        }
        echo "This never gets output.<br />\n";
    }
    echo "Neither does this.<br />\n";
}
?>

Omitting the semicolon after continue can lead to confusion. Here's an example of what you shouldn't do.

<?php
for ($i = 0; $i < 5; ++$i) {
    if ($i == 2)
        continue
    print "$i\n";
}
?>

One can expect the result to be:

0
1
3
4

but this script will output:

2

because the entire continue print "$i\n"; is evaluated as a single expression, and so print() is called only when $i == 2 is true. (The return value of print is passed to continue as the numeric argument.)

=====================================================================


switch

The switch statement is similar to a series of IF statements on the same expression. In many occasions, you may want to compare the same variable (or expression) with many different values, and execute a different piece of code depending on which value it equals to. This is exactly what the switch statement is for.

    Note: Note that unlike some other languages, the continue statement applies to switch and acts similar to break. If you have a switch inside a loop and wish to continue to the next iteration of the outer loop, use continue 2. 

    Note:

    Note that switch/case does loose comparision.

The following two examples are two different ways to write the same thing, one using a series of if and elseif statements, and the other using the switch statement:

Example #1 switch structure
<?php
if ($i == 0) {
    echo "i equals 0";
} elseif ($i == 1) {
    echo "i equals 1";
} elseif ($i == 2) {
    echo "i equals 2";
}

switch ($i) {
    case 0:
        echo "i equals 0";
        break;
    case 1:
        echo "i equals 1";
        break;
    case 2:
        echo "i equals 2";
        break;
}
?>

Example #2 switch structure allows usage of strings
<?php
switch ($i) {
    case "apple":
        echo "i is apple";
        break;
    case "bar":
        echo "i is bar";
        break;
    case "cake":
        echo "i is cake";
        break;
}
?>

It is important to understand how the switch statement is executed in order to avoid mistakes. The switch statement executes line by line (actually, statement by statement). In the beginning, no code is executed. Only when a case statement is found with a value that matches the value of the switch expression does PHP begin to execute the statements. PHP continues to execute the statements until the end of the switch block, or the first time it sees a break statement. If you don't write a break statement at the end of a case's statement list, PHP will go on executing the statements of the following case. For example:
<?php
switch ($i) {
    case 0:
        echo "i equals 0";
    case 1:
        echo "i equals 1";
    case 2:
        echo "i equals 2";
}
?>

Here, if $i is equal to 0, PHP would execute all of the echo statements! If $i is equal to 1, PHP would execute the last two echo statements. You would get the expected behavior ('i equals 2' would be displayed) only if $i is equal to 2. Thus, it is important not to forget break statements (even though you may want to avoid supplying them on purpose under certain circumstances).

In a switch statement, the condition is evaluated only once and the result is compared to each case statement. In an elseif statement, the condition is evaluated again. If your condition is more complicated than a simple compare and/or is in a tight loop, a switch may be faster.

The statement list for a case can also be empty, which simply passes control into the statement list for the next case.
<?php
switch ($i) {
case 0:
case 1:
case 2:
    echo "i is less than 3 but not negative";
    break;
case 3:
    echo "i is 3";
}
?>

A special case is the default case. This case matches anything that wasn't matched by the other cases. For example:
<?php
switch ($i) {
    case 0:
        echo "i equals 0";
        break;
    case 1:
        echo "i equals 1";
        break;
    case 2:
        echo "i equals 2";
        break;
    default:
       echo "i is not equal to 0, 1 or 2";
}
?>

The case expression may be any expression that evaluates to a simple type, that is, integer or floating-point numbers and strings. Arrays or objects cannot be used here unless they are dereferenced to a simple type.

The alternative syntax for control structures is supported with switches. For more information, see Alternative syntax for control structures.
<?php
switch ($i):
    case 0:
        echo "i equals 0";
        break;
    case 1:
        echo "i equals 1";
        break;
    case 2:
        echo "i equals 2";
        break;
    default:
        echo "i is not equal to 0, 1 or 2";
endswitch;
?>

Its possible to use a semicolon instead of a colon after a case like:
<?php
switch($beer)
{
    case 'tuborg';
    case 'carlsberg';
    case 'heineken';
        echo 'Good choice';
    break;
    default;
        echo 'Please make a new selection...';
    break;
}
?>

=====================================================================


declare

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
    statement

The directive section allows the behavior of the declare block to be set. Currently only two directives are recognized: the ticks directive (See below for more information on the ticks directive) and the encoding directive (See below for more information on the encoding directive).

    Note: The encoding directive was added in PHP 5.3.0 

The statement part of the declare block will be executed - how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it (however if the file with declare was included then it does not affect the parent file).
<?php
// these are the same:

// you can use this:
declare(ticks=1) {
    // entire script here
}

// or you can use this:
declare(ticks=1);
// entire script here
?>
Ticks

A tick is an event that occurs for every N low-level tickable statements executed by the parser within the declare block. The value for N is specified using ticks=N within the declare blocks's directive section.

Not all statements are tickable. Typically, condition expressions and argument expressions are not tickable.

The event(s) that occur on each tick are specified using the register_tick_function(). See the example below for more details. Note that more than one event can occur for each tick.

Example #1 Tick usage example
<?php

declare(ticks=1);

// A function called on each tick event
function tick_handler()
{
    echo "tick_handler() called\n";
}

register_tick_function('tick_handler');

$a = 1;

if ($a > 0) {
    $a += 2;
    print($a);
}

?>

Example #2 Ticks usage example
<?php

function tick_handler()
{
  echo "tick_handler() called\n";
}

$a = 1;
tick_handler();

if ($a > 0) {
    $a += 2;
    tick_handler();
    print($a);
    tick_handler();
}
tick_handler();

?>

See also register_tick_function() and unregister_tick_function().
Encoding

A script's encoding can be specified per-script using the encoding directive.

Example #3 Declaring an encoding for the script.
<?php
declare(encoding='ISO-8859-1');
// code here
?>
Caution

When combined with namespaces, the only legal syntax for declare is declare(encoding='...'); where ... is the encoding value. declare(encoding='...') {} will result in a parse error when combined with namespaces.

The encoding declare value is ignored in PHP 5.3 unless php is compiled with --enable-zend-multibyte.

Note that PHP does not expose whether --enable-zend-multibyte was used to compile PHP other than by phpinfo().

=====================================================================


return

If called from within a function, the return() statement immediately ends execution of the current function, and returns its argument as the value of the function call. return() will also end the execution of an eval() statement or script file.

If called from the global scope, then execution of the current script file is ended. If the current script file was include()ed or require()ed, then control is passed back to the calling file. Furthermore, if the current script file was include()ed, then the value given to return() will be returned as the value of the include() call. If return() is called from within the main script file, then script execution ends. If the current script file was named by the auto_prepend_file or auto_append_file configuration options in php.ini, then that script file's execution is ended.

For more information, see Returning values.

    Note: Note that since return() is a language construct and not a function, the parentheses surrounding its arguments are not required. It is common to leave them out, and you actually should do so as PHP has less work to do in this case. 

    Note: If no parameter is supplied, then the parentheses must be omitted and NULL will be returned. Calling return() with parentheses but with no arguments will result in a parse error. 

    Note: You should never use parentheses around your return variable when returning by reference, as this will not work. You can only return variables by reference, not the result of a statement. If you use return ($a); then you're not returning a variable, but the result of the expression ($a) (which is, of course, the value of $a). 

=====================================================================

require()

require() is identical to include() except upon failure it will also produce a fatal E_COMPILE_ERROR level error. In other words, it will halt the script whereas include() only emits a warning (E_WARNING) which allows the script to continue.

See the include() documentation for how this works.

=====================================================================


include()

The include() statement includes and evaluates the specified file.

The documentation below also applies to require().

Files are included based on the file path given or, if none is given, the include_path specified. If the file isn't found in the include_path, include() will finally check in the calling script's own directory and the current working directory before failing. The include() construct will emit a warning if it cannot find a file; this is different behavior from require(), which will emit a fatal error.

If a path is defined — whether absolute (starting with a drive letter or \ on Windows, or / on Unix/Linux systems) or relative to the current directory (starting with . or ..) — the include_path will be ignored altogether. For example, if a filename begins with ../, the parser will look in the parent directory to find the requested file.

For more information on how PHP handles including files and the include path, see the documentation for include_path.

When a file is included, the code it contains inherits the variable scope of the line on which the include occurs. Any variables available at that line in the calling file will be available within the called file, from that point forward. However, all functions and classes defined in the included file have the global scope.

Example #1 Basic include() example
vars.php
<?php

$color = 'green';
$fruit = 'apple';

?>

test.php
<?php

echo "A $color $fruit"; // A

include 'vars.php';

echo "A $color $fruit"; // A green apple

?>

If the include occurs inside a function within the calling file, then all of the code contained in the called file will behave as though it had been defined inside that function. So, it will follow the variable scope of that function. An exception to this rule are magic constants which are evaluated by the parser before the include occurs.

Example #2 Including within functions
<?php

function foo()
{
    global $color;

    include 'vars.php';

    echo "A $color $fruit";
}

/* vars.php is in the scope of foo() so     *
* $fruit is NOT available outside of this  *
* scope.  $color is because we declared it *
* as global.                               */

foo();                    // A green apple
echo "A $color $fruit";   // A green

?>

When a file is included, parsing drops out of PHP mode and into HTML mode at the beginning of the target file, and resumes again at the end. For this reason, any code inside the target file which should be executed as PHP code must be enclosed within valid PHP start and end tags.

If "URL fopen wrappers" are enabled in PHP (which they are in the default configuration), you can specify the file to be included using a URL (via HTTP or other supported wrapper - see Supported Protocols and Wrappers for a list of protocols) instead of a local pathname. If the target server interprets the target file as PHP code, variables may be passed to the included file using a URL request string as used with HTTP GET. This is not strictly speaking the same thing as including the file and having it inherit the parent file's variable scope; the script is actually being run on the remote server and the result is then being included into the local script.
Warning

Windows versions of PHP prior to PHP 4.3.0 do not support access of remote files via this function, even if allow_url_fopen is enabled.

Example #3 include() through HTTP
<?php

/* This example assumes that www.example.com is configured to parse .php
* files and not .txt files. Also, 'Works' here means that the variables
* $foo and $bar are available within the included file. */

// Won't work; file.txt wasn't handled by www.example.com as PHP
include 'http://www.example.com/file.txt?foo=1&bar=2';

// Won't work; looks for a file named 'file.php?foo=1&bar=2' on the
// local filesystem.
include 'file.php?foo=1&bar=2';

// Works.
include 'http://www.example.com/file.php?foo=1&bar=2';

$foo = 1;
$bar = 2;
include 'file.txt';  // Works.
include 'file.php';  // Works.

?>
Warning
Security warning

Remote file may be processed at the remote server (depending on the file extension and the fact if the remote server runs PHP or not) but it still has to produce a valid PHP script because it will be processed at the local server. If the file from the remote server should be processed there and outputted only, readfile() is much better function to use. Otherwise, special care should be taken to secure the remote script to produce a valid and desired code.

See also Remote files, fopen() and file() for related information.

Handling Returns: It is possible to execute a return() statement inside an included file in order to terminate processing in that file and return to the script which called it. Also, it's possible to return values from included files. You can take the value of the include call as you would a normal function. This is not, however, possible when including remote files unless the output of the remote file has valid PHP start and end tags (as with any local file). You can declare the needed variables within those tags and they will be introduced at whichever point the file was included.

Because include() is a special language construct, parentheses are not needed around its argument. Take care when comparing return value.

Example #4 Comparing return value of include
<?php
// won't work, evaluated as include(('vars.php') == 'OK'), i.e. include('')
if (include('vars.php') == 'OK') {
    echo 'OK';
}

// works
if ((include 'vars.php') == 'OK') {
    echo 'OK';
}
?>

Example #5 include() and the return() statement
return.php
<?php

$var = 'PHP';

return $var;

?>

noreturn.php
<?php

$var = 'PHP';

?>

testreturns.php
<?php

$foo = include 'return.php';

echo $foo; // prints 'PHP'

$bar = include 'noreturn.php';

echo $bar; // prints 1

?>

$bar is the value 1 because the include was successful. Notice the difference between the above examples. The first uses return() within the included file while the other does not. If the file can't be included, FALSE is returned and E_WARNING is issued.

If there are functions defined in the included file, they can be used in the main file independent if they are before return() or after. If the file is included twice, PHP 5 issues fatal error because functions were already declared, while PHP 4 doesn't complain about functions defined after return(). It is recommended to use include_once() instead of checking if the file was already included and conditionally return inside the included file.

Another way to "include" a PHP file into a variable is to capture the output by using the Output Control Functions with include(). For example:

Example #6 Using output buffering to include a PHP file into a string
<?php
$string = get_include_contents('somefile.php');

function get_include_contents($filename) {
    if (is_file($filename)) {
        ob_start();
        include $filename;
        return ob_get_clean();
    }
    return false;
}

?>

In order to automatically include files within scripts, see also the auto_prepend_file and auto_append_file configuration options in php.ini.

    Note: Because this is a language construct and not a function, it cannot be called using variable functions 

See also require(), require_once(), include_once(), get_included_files(), readfile(), virtual(), and include_path.

=====================================================================


require_once()

The require_once() statement is identical to require() except PHP will check if the file has already been included, and if so, not include (require) it again.

See the include_once() documentation for information about the _once behaviour, and how it differs from its non _once siblings.

=====================================================================


include_once()

The include_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include() statement, with the only difference being that if the code from a file has already been included, it will not be included again. As the name suggests, it will be included just once.

include_once() may be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, so in this case it may help avoid problems such as function redefinitions, variable value reassignments, etc.

See the include() documentation for information about how this function works.

    Note:

    With PHP 4, _once functionality differs with case-insensitive operating systems (like Windows) so for example:

    Example #1 include_once() with a case insensitive OS in PHP 4
    <?php
    include_once "a.php"; // this will include a.php
    include_once "A.php"; // this will include a.php again! (PHP 4 only)
    ?>

    This behaviour changed in PHP 5, so for example with Windows the path is normalized first so that C:\PROGRA~1\A.php is realized the same as C:\Program Files\a.php and the file is included just once.

=====================================================================

goto

The goto operator can be used to jump to another section in the program. The target point is specified by a label followed by a colon, and the instruction is given as goto followed by the desired target label. This is not a full unrestricted goto. The target label must be within the same file and context, meaning that you cannot jump out of a function or method, nor can you jump into one. You also cannot jump into any sort of loop or switch structure. You may jump out of these, and a common use is to use a goto in place of a multi-level break.

Example #1 goto example
<?php
goto a;
echo 'Foo';
 
a:
echo 'Bar';
?>

The above example will output:

Bar

Example #2 goto loop example
<?php
for($i=0,$j=50; $i<100; $i++) {
  while($j--) {
    if($j==17) goto end; 
  }  
}
echo "i = $i";
end:
echo 'j hit 17';
?>

The above example will output:

j hit 17

Example #3 This will not work
<?php
goto loop;
for($i=0,$j=50; $i<100; $i++) {
  while($j--) {
    loop:
  }
}
echo "$i = $i";
?>

The above example will output:

Fatal error: 'goto' into loop or switch statement is disallowed in
script on line 2

Note:
  The goto operator is available as of PHP 5.3.

  Use of the goto operator is frowned upon as it can make it very 
  difficult to debug and track down problems later on because 
  it is so easy to jump way out of the obvious visual brogram flow.

=====================================================================
=====================================================================
    * Functions
=====================================================================

Table of Contents

    * User-defined functions
    * Function arguments
    * Returning values
    * Variable functions
    * Internal (built-in) functions
    * Anonymous functions

=====================================================================


User-defined functions

A function may be defined using syntax such as the following:

Example #1 Pseudo code to demonstrate function uses
<?php
function foo($arg_1, $arg_2, /* ..., */ $arg_n)
{
    echo "Example function.\n";
    return $retval;
}
?>

Any valid PHP code may appear inside a function, even other functions and class definitions.

Function names follow the same rules as other labels in PHP. A valid function name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*.
Tip

See also the Userland Naming Guide.

Functions need not be defined before they are referenced, except when a function is conditionally defined as shown in the two examples below.

When a function is defined in a conditional manner such as the two examples shown. Its definition must be processed prior to being called.

Example #2 Conditional functions
<?php

$makefoo = true;

/* We can't call foo() from here 
   since it doesn't exist yet,
   but we can call bar() */

bar();

if ($makefoo) {
  function foo()
  {
    echo "I don't exist until program execution reaches me.\n";
  }
}

/* Now we can safely call foo()
   since $makefoo evaluated to true */

if ($makefoo) foo();

function bar() 
{
  echo "I exist immediately upon program start.\n";
}

?>

Example #3 Functions within functions
<?php
function foo() 
{
  function bar() 
  {
    echo "I don't exist until foo() is called.\n";
  }
}

/* We can't call bar() yet
   since it doesn't exist. */

foo();

/* Now we can call bar(),
   foo()'s processesing has
   made it accessible. */

bar();

?>

All functions and classes in PHP have the global scope - they can be called outside a function even if they were defined inside and vice versa.

PHP does not support function overloading, nor is it possible to undefine or redefine previously-declared functions.

    Note: Function names are case-insensitive, though it is usually good form to call functions as they appear in their declaration. 

Both variable number of arguments and default arguments are supported in functions. See also the function references for func_num_args(), func_get_arg(), and func_get_args() for more information.

It is possible to call recursive functions in PHP. However avoid recursive function/method calls with over 100-200 recursion levels as it can smash the stack and cause a termination of the current script.

Example #4 Recursive functions
<?php
function recursion($a)
{
    if ($a < 20) {
        echo "$a\n";
        recursion($a + 1);
    }
}
?>

=====================================================================


Function arguments

Information may be passed to functions via the argument list, which is a comma-delimited list of expressions.

PHP supports passing arguments by value (the default), passing by reference, and default argument values. Variable-length argument lists are also supported, see also the function references for func_num_args(), func_get_arg(), and func_get_args() for more information.

Example #1 Passing arrays to functions
<?php
function takes_array($input)
{
    echo "$input[0] + $input[1] = ", $input[0]+$input[1];
}
?>
Making arguments be passed by reference

By default, function arguments are passed by value (so that if the value of the argument within the function is changed, it does not get changed outside of the function). To allow a function to modify its arguments, they must be passed by reference.

To have an argument to a function always passed by reference, prepend an ampersand (&) to the argument name in the function definition:

Example #2 Passing function parameters by reference
<?php
function add_some_extra(&$string)
{
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // outputs 'This is a string, and something extra.'
?>
Default argument values

A function may define C++-style default values for scalar arguments as follows:

Example #3 Use of default parameters in functions
<?php
function makecoffee($type = "cappuccino")
{
    return "Making a cup of $type.\n";
}
echo makecoffee();
echo makecoffee(null);
echo makecoffee("espresso");
?>

The above example will output:

Making a cup of cappuccino.
Making a cup of .
Making a cup of espresso.

PHP also allows the use of arrays and the special type NULL as default values, for example:

Example #4 Using non-scalar types as default values
<?php
function makecoffee($types = array("cappuccino"), $coffeeMaker = NULL)
{
    $device = is_null($coffeeMaker) ? "hands" : $coffeeMaker;
    return "Making a cup of ".join(", ", $types)." with $device.\n";
}
echo makecoffee();
echo makecoffee(array("cappuccino", "lavazza"), "teapot");
?>

The default value must be a constant expression, not (for example) a variable, a class member or a function call.

Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected. Consider the following code snippet:

Example #5 Incorrect usage of default function arguments
<?php
function makeyogurt($type = "acidophilus", $flavour)
{
    return "Making a bowl of $type $flavour.\n";
}
 
echo makeyogurt("raspberry");   // won't work as expected
?>

The above example will output:

Warning: Missing argument 2 in call to makeyogurt() in 
/usr/local/etc/httpd/htdocs/phptest/functest.html on line 41
Making a bowl of raspberry .

Now, compare the above with this:

Example #6 Correct usage of default function arguments
<?php
function makeyogurt($flavour, $type = "acidophilus")
{
    return "Making a bowl of $type $flavour.\n";
}
 
echo makeyogurt("raspberry");   // works as expected
?>

The above example will output:

Making a bowl of acidophilus raspberry.

    Note: As of PHP 5, default values may be passed by reference. 

Variable-length argument lists

PHP 4 and above has support for variable-length argument lists in user-defined functions. This is really quite easy, using the func_num_args(), func_get_arg(), and func_get_args() functions.

No special syntax is required, and argument lists may still be explicitly provided with function definitions and will behave as normal.

=====================================================================


Returning values

Values are returned by using the optional return statement. Any type may be returned, including arrays and objects. This causes the function to end its execution immediately and pass control back to the line from which it was called. See return() for more information.

    Note:

    If the return() is omitted the value NULL will be returned.

Example #1 Use of return()
<?php
function square($num)
{
    return $num * $num;
}
echo square(4);   // outputs '16'.
?>

A function can not return multiple values, but similar results can be obtained by returning an array.

Example #2 Returning an array to get multiple values
<?php
function small_numbers()
{
    return array (0, 1, 2);
}
list ($zero, $one, $two) = small_numbers();
?>

To return a reference from a function, use the reference operator & in both the function declaration and when assigning the returned value to a variable:

Example #3 Returning a reference from a function
<?php
function &returns_reference()
{
    return $someref;
}

$newref =& returns_reference();
?>

For more information on references, please check out References Explained.

=====================================================================


Variable functions

PHP supports the concept of variable functions. This means that if a variable name has parentheses appended to it, PHP will look for a function with the same name as whatever the variable evaluates to, and will attempt to execute it. Among other things, this can be used to implement callbacks, function tables, and so forth.

Variable functions won't work with language constructs such as echo(), print(), unset(), isset(), empty(), include(), require() and the like. Utilize wrapper functions to make use of any of these constructs as variable functions.

Example #1 Variable function example
<?php
function foo() {
    echo "In foo()<br />\n";
}

function bar($arg = '')
{
    echo "In bar(); argument was '$arg'.<br />\n";
}

// This is a wrapper function around echo
function echoit($string)
{
    echo $string;
}

$func = 'foo';
$func();        // This calls foo()

$func = 'bar';
$func('test');  // This calls bar()

$func = 'echoit';
$func('test');  // This calls echoit()
?>

An object method can also be called with the variable functions syntax.

Example #2 Variable method example
<?php
class Foo
{
    function Variable()
    {
        $name = 'Bar';
        $this->$name(); // This calls the Bar() method
    }
    
    function Bar()
    {
        echo "This is Bar";
    }
}

$foo = new Foo();
$funcname = "Variable";
$foo->$funcname();  // This calls $foo->Variable()

?>

When calling static methods, the function call is stronger than the static property operator:

Example #3 Variable method example with static properties
<?php
class Foo
{
    static $variable = 'static property';
    static function Variable()
    {
        echo 'Method Variable called';
    }
}

echo Foo::$variable; // This prints 'static property'. It does need a $variable in this scope.
$variable = "Variable";
Foo::$variable();  // This calls $foo->Variable() reading $variable in this scope.

?>

See also call_user_func(), variable variables and function_exists().

=====================================================================


Internal (built-in) functions

PHP comes standard with many functions and constructs. There are also functions that require specific PHP extensions compiled in, otherwise fatal "undefined function" errors will appear. For example, to use image functions such as imagecreatetruecolor(), PHP must be compiled with GD support. Or, to use mysql_connect(), PHP must be compiled with MySQL support. There are many core functions that are included in every version of PHP, such as the string and variable functions. A call to phpinfo() or get_loaded_extensions() will show which extensions are loaded into PHP. Also note that many extensions are enabled by default and that the PHP manual is split up by extension. See the configuration, installation, and individual extension chapters, for information on how to set up PHP.

Reading and understanding a function's prototype is explained within the manual section titled how to read a function definition. It's important to realize what a function returns or if a function works directly on a passed in value. For example, str_replace() will return the modified string while usort() works on the actual passed in variable itself. Each manual page also has specific information for each function like information on function parameters, behavior changes, return values for both success and failure, and availability information. Knowing these important (yet often subtle) differences is crucial for writing correct PHP code.

    Note: If the parameters given to a function are not what it expects, such as passing an array where a string is expected, the return value of the function is undefined. In this case it will likely return NULL but this is just a convention, and cannot be relied upon. 

See also function_exists(), the function reference, get_extension_funcs(), and dl().

=====================================================================


Anonymous functions

Anonymous functions, also known as closures, allow the creation of functions which have no specified name. They are most useful as the value of callback parameters, but they have many other uses.

Example #1 Anonymous function example
<?php
echo preg_replace_callback('~-([a-z])~', function ($match) {
    return strtoupper($match[1]);
}, 'hello-world');
// outputs helloWorld
?>

Closures can also be used as the values of variables; PHP automatically converts such expressions into instances of the Closure internal class. Assigning a closure to a variable uses the same syntax as any other assignment, including the trailing semicolon:

Example #2 Anonymous function variable assignment example
<?php
$greet = function($name)
{
    printf("Hello %s\r\n", $name);
};

$greet('World');
$greet('PHP');
?>

Closures may also inherit variables from the parent scope. Any such variables must be declared in the function header. Inheriting variables from the parent scope is not the same as using global variables. Global variables exist in the global scope, which is the same no matter what function is executing. The parent scope of a closure is the function in which the closure was declared (not necessarily the function it was called from). See the following example:

Example #3 Closures and scoping
<?php
// A basic shopping cart which contains a list of added products
// and the quantity of each product. Includes a method which
// calculates the total price of the items in the cart using a
// closure as a callback.
class Cart
{
    const PRICE_BUTTER  = 1.00;
    const PRICE_MILK    = 3.00;
    const PRICE_EGGS    = 6.95;

    protected $products = array();
    
    public function add($product, $quantity)
    {
        $this->products[$product] = $quantity;
    }
    
    public function getQuantity($product)
    {
        return isset($this->products[$product]) ? $this->products[$product] :
               FALSE;
    }
    
    public function getTotal($tax)
    {
        $total = 0.00;
        
        $callback =
            function ($quantity, $product) use ($tax, &$total)
            {
                $pricePerItem = constant(__CLASS__ . "::PRICE_" .
                    strtoupper($product));
                $total += ($pricePerItem * $quantity) * ($tax + 1.0);
            };
        
        array_walk($this->products, $callback);
        return round($total, 2);
    }
}

$my_cart = new Cart;

// Add some items to the cart
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);

// Print the total with a 5% sales tax.
print $my_cart->getTotal(0.05) . "\n";
// The result is 54.29
?>

Anonymous functions are currently implemented using the Closure class. This is an implementation detail and should not be relied upon.

    Note: Anonymous functions are available since PHP 5.3.0. 

    Note: It was not possible to use $this from anonymous function before PHP 5.4.0. 

    Note: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within a closure. 

=====================================================================
=====================================================================
    * Classes and Objects
=====================================================================

Table of Contents
    * Introduction
    * The Basics
    * Properties
    * Class Constants
    * Autoloading Classes
    * Constructors and Destructors
    * Visibility
    * Object Inheritance
    * Scope Resolution Operator (::)
    * Static Keyword
    * Class Abstraction
    * Object Interfaces
    * Overloading
    * Object Iteration
    * Patterns
    * Magic Methods
    * Final Keyword
    * Object Cloning
    * Comparing Objects
    * Type Hinting
    * Late Static Bindings
    * Objects and references
    * Object Serialization
    * OOP Changelog

=====================================================================

Introduction

Starting with PHP 5, the object model was rewritten to allow for better performance and more features. This was a major change from PHP 4. PHP 5 has a full object model.

Among the features in PHP 5 are the inclusions of visibility, abstract and final classes and methods, additional magic methods, interfaces, cloning and typehinting.

PHP treats objects in the same way as references or handles, meaning that each variable contains an object reference rather than a copy of the entire object. See Objects and References
Tip

See also the Userland Naming Guide.

=====================================================================


The Basics
class

Basic class definitions begin with the keyword class, followed by a class name, followed by a pair of curly braces which enclose the definitions of the properties and methods belonging to the class.

The class name can be any valid label which is a not a PHP reserved word. A valid class name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*.

A class may contain its own constants, variables (called "properties"), and functions (called "methods").

Example #1 Simple Class definition
<?php
class SimpleClass
{
    // property declaration
    public $var = 'a default value';

    // method declaration
    public function displayVar() {
        echo $this->var;
    }
}
?>

The pseudo-variable $this is available when a method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but possibly another object, if the method is called statically from the context of a secondary object).

Example #2 Some examples of the $this pseudo-variable
<?php
class A
{
    function foo()
    {
        if (isset($this)) {
            echo '$this is defined (';
            echo get_class($this);
            echo ")\n";
        } else {
            echo "\$this is not defined.\n";
        }
    }
}

class B
{
    function bar()
    {
        // Note: the next line will issue a warning if E_STRICT is enabled.
        A::foo();
    }
}

$a = new A();
$a->foo();

// Note: the next line will issue a warning if E_STRICT is enabled.
A::foo();
$b = new B();
$b->bar();

// Note: the next line will issue a warning if E_STRICT is enabled.
B::bar();
?>

The above example will output:

$this is defined (A)
$this is not defined.
$this is defined (B)
$this is not defined.

new

To create an instance of a class, the new keyword must be used. An object will always be created unless the object has a constructor defined that throws an exception on error. Classes should be defined before instantiation (and in some cases this is a requirement).

If a string containing the name of a class is used with new, a new instance of that class will be created. If the class is in a namespace, its fully qualified name must be used when doing this.

Example #3 Creating an instance
<?php
$instance = new SimpleClass();

// This can also be done with a variable:
$className = 'Foo';
$instance = new $className(); // Foo()
?>

In the class context, it is possible to create a new object by new self and new parent.

When assigning an already created instance of a class to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A copy of an already created object can be made by cloning it.

Example #4 Object Assignment
<?php

$instance = new SimpleClass();

$assigned   =  $instance;
$reference  =& $instance;

$instance->var = '$assigned will have this value';

$instance = null; // $instance and $reference become null

var_dump($instance);
var_dump($reference);
var_dump($assigned);
?>

The above example will output:

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

PHP 5.3.0 introduced a couple of new ways to create instances of an object:

Example #5 Creating new objects
<?php
class Test
{
    static public function getNew()
    {
        return new static;
    }
}

class Child extends Test
{}

$obj1 = new Test();
$obj2 = new $obj1;
var_dump($obj1 !== $obj2);

$obj3 = Test::getNew();
var_dump($obj3 instanceof Test);

$obj4 = Child::getNew();
var_dump($obj4 instanceof Child);
?>

The above example will output:

bool(true)
bool(true)
bool(true)

extends

A class can inherit the methods and properties of another class by using the keyword extends in the class declaration. It is not possible to extend multiple classes; a class can only inherit from one base class.

The inherited methods and properties can be overridden by redeclaring them with the same name defined in the parent class. However, if the parent class has defined a method as final, that method may not be overridden. It is possible to access the overridden methods or static properties by referencing them with parent::.

When overriding methods, the parameter signature should remain the same or PHP will generate an E_STRICT level error. This does not apply to the constructor, which allows overriding with different parameters.

Example #6 Simple Class Inheritance
<?php
class ExtendClass extends SimpleClass
{
    // Redefine the parent method
    function displayVar()
    {
        echo "Extending class\n";
        parent::displayVar();
    }
}

$extended = new ExtendClass();
$extended->displayVar();
?>

The above example will output:

Extending class
a default value

=====================================================================


Properties

Class member variables are called "properties". You may also see them referred to using other terms such as "attributes" or "fields", but for the purposes of this reference we will use "properties". They are defined by using one of the keywords public, protected, or private, followed by a normal variable declaration. This declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

See Visibility for more information on the meanings of public, protected, and private.

    Note:

    In order to maintain backward compatibility with PHP 4, PHP 5 will still accept the use of the keyword var in property declarations instead of (or in addition to) public, protected, or private. However, var is no longer required. In versions of PHP from 5.0 to 5.1.3, the use of var was considered deprecated and would issue an E_STRICT warning, but since PHP 5.1.3 it is no longer deprecated and does not issue the warning.

    If you declare a property using var instead of one of public, protected, or private, then PHP 5 will treat the property as if it had been declared as public.

Within class methods the properties, constants, and methods may be accessed by using the form $this->property (where property is the name of the property) unless the access is to a static property within the context of a static class method, in which case it is accessed using the form self::$property. See Static Keyword for more information.

The pseudo-variable $this is available inside any class method when that method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but possibly another object, if the method is called statically from the context of a secondary object).

Example #1 property declarations
<?php
class SimpleClass
{
   // invalid property declarations:
   public $var1 = 'hello ' . 'world';
   public $var2 = <<<EOD
hello world
EOD;
   public $var3 = 1+2;
   public $var4 = self::myStaticMethod();
   public $var5 = $myVar;

   // valid property declarations:
   public $var6 = myConstant;
   public $var7 = array(true, false);

   // This is allowed only in PHP 5.3.0 and later.
   public $var8 = <<<'EOD'
hello world
EOD;
}
?>

Note:
  There are some nice functions to handle classes and objects. You might want to take a look at the Class/Object Functions.

Unlike heredocs, nowdocs can be used in any static data context, including property declarations.

Example #2 Example of using a nowdoc to initialize a property
<?php
class foo {
   // As of PHP 5.3.0
   public $bar = <<<'EOT'
bar
EOT;
}
?>

Note:
  Nowdoc support was added in PHP 5.3.0.

=====================================================================


Class Constants

It is possible to define constant values on a per-class basis remaining the same and unchangeable. Constants differ from normal variables in that you don't use the $ symbol to declare or use them.

The value must be a constant expression, not (for example) a variable, a property, a result of a mathematical operation, or a function call.

It's also possible for interfaces to have constants. Look at the interface documentation for examples.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

Example #1 Defining and using a constant
<?php
class MyClass
{
    const constant = 'constant value';

    function showConstant() {
        echo  self::constant . "\n";
    }
}

echo MyClass::constant . "\n";

$classname = "MyClass";
echo $classname::constant . "\n"; // As of PHP 5.3.0

$class = new MyClass();
$class->showConstant();

echo $class::constant."\n"; // As of PHP 5.3.0
?>

Example #2 Static data example
<?php
class foo {
    // As of PHP 5.3.0
    const bar = <<<'EOT'
bar
EOT;
}
?>

Unlike heredocs, nowdocs can be used in any static data context.

    Note:

    Nowdoc support was added in PHP 5.3.0.

=====================================================================


Autoloading Classes

Many developers writing object-oriented applications create one PHP source file per-class definition. One of the biggest annoyances is having to write a long list of needed includes at the beginning of each script (one for each class).

In PHP 5, this is no longer necessary. You may define an __autoload function which is automatically called in case you are trying to use a class/interface which hasn't been defined yet. By calling this function the scripting engine is given a last chance to load the class before PHP fails with an error.

    Note:

    Prior to 5.3.0, exceptions thrown in the __autoload function could not be caught in the catch block and would result in a fatal error. From 5.3.0+ exceptions thrown in the __autoload function can be caught in the catch block, with 1 provision. If throwing a custom exception, then the custom exception class must be available. The __autoload function may be used recursively to autoload the custom exception class.

    Note:

    Autoloading is not available if using PHP in CLI interactive mode.

    Note:

    If the class name is used e.g. in call_user_func() then it can contain some dangerous characters such as ../. It is recommended to not use the user-input in such functions or at least verify the input in __autoload().

Example #1 Autoload example

This example attempts to load the classes MyClass1 and MyClass2 from the files MyClass1.php and MyClass2.php respectively.
<?php
function __autoload($class_name) {
    include $class_name . '.php';
}

$obj  = new MyClass1();
$obj2 = new MyClass2(); 
?>

Example #2 Autoload other example

This example attempts to load the interface ITest.
<?php

function __autoload($name) {
    var_dump($name);
}

class Foo implements ITest {
}

/*
string(5) "ITest"

Fatal error: Interface 'ITest' not found in ...
*/
?>

Example #3 Autoloading with exception handling for 5.3.0+

This example throws an exception and demonstrates the try/catch block.
<?php
function __autoload($name) {
    echo "Want to load $name.\n";
    throw new Exception("Unable to load $name.");
}

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>

The above example will output:

Want to load NonLoadableClass.
Unable to load NonLoadableClass.

Example #4 Autoloading with exception handling for 5.3.0+ - Missing custom exception

This example throws an exception for a non-loadable, custom exception.
<?php
function __autoload($name) {
    echo "Want to load $name.\n";
    throw new MissingException("Unable to load $name.");
}

try {
    $obj = new NonLoadableClass();
} catch (Exception $e) {
    echo $e->getMessage(), "\n";
}
?>

The above example will output:

Want to load NonLoadableClass.
Want to load MissingException.

Fatal error: Class 'MissingException' not found in testMissingException.php on line 4

See Also

    * unserialize()
    * unserialize_callback_func
    * spl_autoload()
    * spl_autoload_register()

=====================================================================


Constructors and Destructors
Constructor
void __construct ([ mixed $args [, $... ]] )

PHP 5 allows developers to declare constructor methods for classes. Classes which have a constructor method call this method on each newly-created object, so it is suitable for any initialization that the object may need before it is used.

    Note: Parent constructors are not called implicitly if the child class defines a constructor. In order to run a parent constructor, a call to parent::__construct() within the child constructor is required. 

Example #1 using new unified constructors
<?php
class BaseClass {
   function __construct() {
       print "In BaseClass constructor\n";
   }
}

class SubClass extends BaseClass {
   function __construct() {
       parent::__construct();
       print "In SubClass constructor\n";
   }
}

$obj = new BaseClass();
$obj = new SubClass();
?>

For backwards compatibility, if PHP 5 cannot find a __construct() function for a given class, it will search for the old-style constructor function, by the name of the class. Effectively, it means that the only case that would have compatibility issues is if the class had a method named __construct() which was used for different semantics.

Unlike with other methods, PHP will not generate an E_STRICT level error message when __construct() is overridden with different parameters than the parent __construct() method has.

As of PHP 5.3.3, methods with the same name as the last element of a namespaced class name will no longer be treated as constructor. This change doesn't affect non-namespaced classes.

Example #2 Constructors in namespaced classes
<?php
namespace Foo;
class Bar {
    public function Bar() {
        // treated as constructor in PHP 5.3.0-5.3.2
        // treated as regular method as of PHP 5.3.3
    }
}
?>
Destructor
void __destruct ( void )

PHP 5 introduces a destructor concept similar to that of other object-oriented languages, such as C++. The destructor method will be called as soon as all references to a particular object are removed or when the object is explicitly destroyed or in any order in shutdown sequence.

Example #3 Destructor Example
<?php
class MyDestructableClass {
   function __construct() {
       print "In constructor\n";
       $this->name = "MyDestructableClass";
   }

   function __destruct() {
       print "Destroying " . $this->name . "\n";
   }
}

$obj = new MyDestructableClass();
?>

Like constructors, parent destructors will not be called implicitly by the engine. In order to run a parent destructor, one would have to explicitly call parent::__destruct() in the destructor body.

The destructor will be called even if script execution is stopped using exit(). Calling exit() in a destructor will prevent the remaining shutdown routines from executing.

    Note:

    Destructors called during the script shutdown have HTTP headers already sent. The working directory in the script shutdown phase can be different with some SAPIs (e.g. Apache).

    Note:

    Attempting to throw an exception from a destructor (called in the time of script termination) causes a fatal error.

=====================================================================


Visibility

The visibility of a property or method can be defined by prefixing the declaration with the keywords public, protected or private. Class members declared public can be accessed everywhere. Members declared protected can be accessed only within the class itself and by inherited and parent classes. Members declared as private may only be accessed by the class that defines the member.
Property Visibility

Class properties must be defined as public, private, or protected. If declared using var, the property will be defined as public.

Example #1 Property declaration
<?php
/**
 * Define MyClass
 */
class MyClass
{
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj = new MyClass();
echo $obj->public; // Works
echo $obj->protected; // Fatal Error
echo $obj->private; // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private


/**
 * Define MyClass2
 */
class MyClass2 extends MyClass
{
    // We can redeclare the public and protected method, but not private
    protected $protected = 'Protected2';

    function printHello()
    {
        echo $this->public;
        echo $this->protected;
        echo $this->private;
    }
}

$obj2 = new MyClass2();
echo $obj2->public; // Works
echo $obj2->private; // Undefined
echo $obj2->protected; // Fatal Error
$obj2->printHello(); // Shows Public, Protected2, Undefined

?>

    Note: The PHP 4 method of declaring a variable with the var keyword is still supported for compatibility reasons (as a synonym for the public keyword). In PHP 5 before 5.1.3, its usage would generate an E_STRICT warning. 

Method Visibility

Class methods may be defined as public, private, or protected. Methods declared without any explicit visibility keyword are defined as public.

Example #2 Method Declaration
<?php
/**
 * Define MyClass
 */
class MyClass
{
    // Declare a public constructor
    public function __construct() { }

    // Declare a public method
    public function MyPublic() { }

    // Declare a protected method
    protected function MyProtected() { }

    // Declare a private method
    private function MyPrivate() { }

    // This is public
    function Foo()
    {
        $this->MyPublic();
        $this->MyProtected();
        $this->MyPrivate();
    }
}

$myclass = new MyClass;
$myclass->MyPublic(); // Works
$myclass->MyProtected(); // Fatal Error
$myclass->MyPrivate(); // Fatal Error
$myclass->Foo(); // Public, Protected and Private work


/**
 * Define MyClass2
 */
class MyClass2 extends MyClass
{
    // This is public
    function Foo2()
    {
        $this->MyPublic();
        $this->MyProtected();
        $this->MyPrivate(); // Fatal Error
    }
}

$myclass2 = new MyClass2;
$myclass2->MyPublic(); // Works
$myclass2->Foo2(); // Public and Protected work, not Private

class Bar 
{
    public function test() {
        $this->testPrivate();
        $this->testPublic();
    }

    public function testPublic() {
        echo "Bar::testPublic\n";
    }
    
    private function testPrivate() {
        echo "Bar::testPrivate\n";
    }
}

class Foo extends Bar 
{
    public function testPublic() {
        echo "Foo::testPublic\n";
    }
    
    private function testPrivate() {
        echo "Foo::testPrivate\n";
    }
}

$myFoo = new foo();
$myFoo->test(); // Bar::testPrivate 
                // Foo::testPublic
?>
Visibility from other objects

Objects of the same type will have access to each others private and protected members even though they are not the same instances. This is because the implementation specific details are already known when inside those objects.

Example #3 Accessing private members of the same object type
<?php
class Test
{
    private $foo;

    public function __construct($foo)
    {
        $this->foo = $foo;
    }

    private function bar()
    {
        echo 'Accessed the private method.';
    }

    public function baz(Test $other)
    {
        // We can change the private property:
        $other->foo = 'hello';
        var_dump($other->foo);

        // We can also call the private method:
        $other->bar();
    }
}

$test = new Test('test');

$test->baz(new Test('other'));
?>

The above example will output:

string(5) "hello"
Accessed the private method.

=====================================================================


Object Inheritance

Inheritance is a well-established programming principle, and PHP makes use of this principle in its object model. This principle will affect the way many classes and objects relate to one another.

For example, when you extend a class, the subclass inherits all of the public and protected methods from the parent class. Unless a class overrides those methods, they will retain their original functionality.

This is useful for defining and abstracting functionality, and permits the implementation of additional functionality in similar objects without the need to reimplement all of the shared functionality.

    Note:

    Unless autoloading is used, then classes must be defined before they are used. If a class extends another, then the parent class must be declared before the child class structure. This rule applies to class that inherit other classes and interfaces.

Example #1 Inheritance Example
<?php

class foo
{
    public function printItem($string)
    {
        echo 'Foo: ' . $string . PHP_EOL;
    }
    
    public function printPHP()
    {
        echo 'PHP is great.' . PHP_EOL;
    }
}

class bar extends foo
{
    public function printItem($string)
    {
        echo 'Bar: ' . $string . PHP_EOL;
    }
}

$foo = new foo();
$bar = new bar();
$foo->printItem('baz'); // Output: 'Foo: baz'
$foo->printPHP();       // Output: 'PHP is great' 
$bar->printItem('baz'); // Output: 'Bar: baz'
$bar->printPHP();       // Output: 'PHP is great'

?>

=====================================================================


Scope Resolution Operator (::)

The Scope Resolution Operator (also called Paamayim Nekudotayim) or in simpler terms, the double colon, is a token that allows access to static, constant, and overridden properties or methods of a class.

When referencing these items from outside the class definition, use the name of the class.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

Paamayim Nekudotayim would, at first, seem like a strange choice for naming a double-colon. However, while writing the Zend Engine 0.5 (which powers PHP 3), that's what the Zend team decided to call it. It actually does mean double-colon - in Hebrew!

Example #1 :: from outside the class definition
<?php
class MyClass {
    const CONST_VALUE = 'A constant value';
}

$classname = 'MyClass';
echo $classname::CONST_VALUE; // As of PHP 5.3.0

echo MyClass::CONST_VALUE;
?>

Two special keywords self and parent are used to access properties or methods from inside the class definition.

Example #2 :: from inside the class definition
<?php
class OtherClass extends MyClass
{
    public static $my_static = 'static var';

    public static function doubleColon() {
        echo parent::CONST_VALUE . "\n";
        echo self::$my_static . "\n";
    }
}

$classname = 'OtherClass';
echo $classname::doubleColon(); // As of PHP 5.3.0

OtherClass::doubleColon();
?>

When an extending class overrides the parents definition of a method, PHP will not call the parent's method. It's up to the extended class on whether or not the parent's method is called. This also applies to Constructors and Destructors, Overloading, and Magic method definitions.

Example #3 Calling a parent's method
<?php
class MyClass
{
    protected function myFunc() {
        echo "MyClass::myFunc()\n";
    }
}

class OtherClass extends MyClass
{
    // Override parent's definition
    public function myFunc()
    {
        // But still call the parent function
        parent::myFunc();
        echo "OtherClass::myFunc()\n";
    }
}

$class = new OtherClass();
$class->myFunc();
?>

=====================================================================


Static Keyword

Declaring class properties or methods as static makes them accessible without needing an instantiation of the class. A property declared as static can not be accessed with an instantiated class object (though a static method can).

For compatibility with PHP 4, if no visibility declaration is used, then the property or method will be treated as if it was declared as public.

Because static methods are callable without an instance of the object created, the pseudo-variable $this is not available inside the method declared as static.

Static properties cannot be accessed through the object using the arrow operator ->.

Calling non-static methods statically generates an E_STRICT level warning.

Like any other PHP static variable, static properties may only be initialized using a literal or constant; expressions are not allowed. So while you may initialize a static property to an integer or array (for instance), you may not initialize it to another variable, to a function return value, or to an object.

As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. self, parent and static).

Example #1 Static property example
<?php
class Foo
{
    public static $my_static = 'foo';

    public function staticValue() {
        return self::$my_static;
    }
}

class Bar extends Foo
{
    public function fooStatic() {
        return parent::$my_static;
    }
}


print Foo::$my_static . "\n";

$foo = new Foo();
print $foo->staticValue() . "\n";
print $foo->my_static . "\n";      // Undefined "Property" my_static 

print $foo::$my_static . "\n";
$classname = 'Foo';
print $classname::$my_static . "\n"; // As of PHP 5.3.0

print Bar::$my_static . "\n";
$bar = new Bar();
print $bar->fooStatic() . "\n";
?>

Example #2 Static method example
<?php
class Foo {
    public static function aStaticMethod() {
        // ...
    }
}

Foo::aStaticMethod();
$classname = 'Foo';
$classname::aStaticMethod(); // As of PHP 5.3.0
?>

=====================================================================


Class Abstraction

PHP 5 introduces abstract classes and methods. Classes defined as abstract may not be instantiated, and any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method's signature - they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent's class declaration must be defined by the child; additionally, these methods must be defined with the same (or a less restricted) visibility. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public, but not private.

Example #1 Abstract class example
<?php
abstract class AbstractClass
{
    // Force Extending class to define this method
    abstract protected function getValue();
    abstract protected function prefixValue($prefix);

    // Common method
    public function printOut() {
        print $this->getValue() . "\n";
    }
}

class ConcreteClass1 extends AbstractClass
{
    protected function getValue() {
        return "ConcreteClass1";
    }

    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass1";
    }
}

class ConcreteClass2 extends AbstractClass
{
    public function getValue() {
        return "ConcreteClass2";
    }

    public function prefixValue($prefix) {
        return "{$prefix}ConcreteClass2";
    }
}

$class1 = new ConcreteClass1;
$class1->printOut();
echo $class1->prefixValue('FOO_') ."\n";

$class2 = new ConcreteClass2;
$class2->printOut();
echo $class2->prefixValue('FOO_') ."\n";
?>

The above example will output:

ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2

Old code that has no user-defined classes or functions named 'abstract' should run without modifications.

=====================================================================


Object Interfaces

Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.

Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.

All methods declared in an interface must be public, this is the nature of an interface.
implements

To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.

    Note:

    A class cannot implement two interfaces that share function names, since it would cause ambiguity.

    Note:

    Interfaces can be extended like classes using the extends operator.

    Note:

    The class implementing the interface must use the exact same method signatures as are defined in the interface. Not doing so will result in a fatal error.

Constants

Its possible for interfaces to have constants. Interface constants works exactly like class constants except they cannot be overridden by a class/interface that inherits it.
Examples

Example #1 Interface example
<?php

// Declare the interface 'iTemplate'
interface iTemplate
{
    public function setVariable($name, $var);
    public function getHtml($template);
}

// Implement the interface
// This will work
class Template implements iTemplate
{
    private $vars = array();
  
    public function setVariable($name, $var)
    {
        $this->vars[$name] = $var;
    }
  
    public function getHtml($template)
    {
        foreach($this->vars as $name => $value) {
            $template = str_replace('{' . $name . '}', $value, $template);
        }
 
        return $template;
    }
}

// This will not work
// Fatal error: Class BadTemplate contains 1 abstract methods
// and must therefore be declared abstract (iTemplate::getHtml)
class BadTemplate implements iTemplate
{
    private $vars = array();
  
    public function setVariable($name, $var)
    {
        $this->vars[$name] = $var;
    }
}
?>

Example #2 Extendable Interfaces
<?php
interface a
{
    public function foo();
}

interface b extends a
{
    public function baz(Baz $baz);
}

// This will work
class c implements b
{
    public function foo()
    {
    }

    public function baz(Baz $baz)
    {
    }
}

// This will not work and result in a fatal error
class d implements b
{
    public function foo()
    {
    }

    public function baz(Foo $foo)
    {
    }
}
?>

Example #3 Multiple interface inheritance
<?php
interface a
{
    public function foo();
}

interface b
{
    public function bar();
}

interface c extends a, b
{
    public function baz();
}

class d implements c
{
    public function foo()
    {
    }

    public function bar()
    {
    }

    public function baz()
    {
    }
}
?>

Example #4 Interfaces with constants
<?php
interface a
{
    const b = 'Interface constant';
}

// Prints: Interface constant
echo a::b;


// This will however not work because its not allowed to 
// override constants.
class b implements a
{
    const b = 'Class constant';
}
?>

An interface, together with type-hinting, provides a good way to make sure that a particular object contains particular methods. See instanceof operator and type hinting.

=====================================================================


Overloading

Overloading in PHP provides means to dynamically "create" properties and methods. These dynamic entities are processed via magic methods one can establish in a class for various action types.

The overloading methods are invoked when interacting with properties or methods that have not been declared or are not visible in the current scope. The rest of this section will use the terms "inaccessible properties" and "inaccessible methods" to refer to this combination of declaration and visibility.

All overloading methods must be defined as public.

    Note:

    None of the arguments of these magic methods can be passed by reference.

    Note:

    PHP's interpretation of "overloading" is different than most object oriented languages. Overloading traditionally provides the ability to have multiple methods with the same name but different quantities and types of arguments.

Changelog

Version 	Description
5.3.0 	Added __callStatic(). Added warning to enforce public visibility and non-static declaration.
5.1.0 	Added __isset() and __unset().
Property overloading
void __set ( string $name , mixed $value )
mixed __get ( string $name )
bool __isset ( string $name )
void __unset ( string $name )

__set() is run when writing data to inaccessible properties.

__get() is utilized for reading data from inaccessible properties.

__isset() is triggered by calling isset() or empty() on inaccessible properties.

__unset() is invoked when unset() is used on inaccessible properties.

The $name argument is the name of the property being interacted with. The __set() method's $value argument specifies the value the $name'ed property should be set to.

Property overloading only works in object context. These magic methods will not be triggered in static context. Therefore these methods should not be declared static. As of PHP 5.3.0, a warning is issued if one of the magic overloading methods is declared static.

    Note:

    The return value of __set() is ignored because of the way PHP processes the assignment operator. Similarly, __get() is never called when chaining assignments together like this:

     $a = $obj->b = 8; 

    Note:

    It is not possible to use overloaded properties in other language constructs than isset(). This means if empty() is called on an overloaded property, the overloaded method is not called.

    To workaround that limitation, the overloaded property must be copied into a local variable in the scope and then be handed to empty().

Example #1 Overloading properties via the __get(), __set(), __isset() and __unset() methods
<?php
class PropertyTest {
    /**  Location for overloaded data.  */
    private $data = array();

    /**  Overloading not used on declared properties.  */
    public $declared = 1;

    /**  Overloading only used on this when accessed outside the class.  */
    private $hidden = 2;

    public function __set($name, $value) {
        echo "Setting '$name' to '$value'\n";
        $this->data[$name] = $value;
    }

    public function __get($name) {
        echo "Getting '$name'\n";
        if (array_key_exists($name, $this->data)) {
            return $this->data[$name];
        }

        $trace = debug_backtrace();
        trigger_error(
            'Undefined property via __get(): ' . $name .
            ' in ' . $trace[0]['file'] .
            ' on line ' . $trace[0]['line'],
            E_USER_NOTICE);
        return null;
    }

    /**  As of PHP 5.1.0  */
    public function __isset($name) {
        echo "Is '$name' set?\n";
        return isset($this->data[$name]);
    }

    /**  As of PHP 5.1.0  */
    public function __unset($name) {
        echo "Unsetting '$name'\n";
        unset($this->data[$name]);
    }

    /**  Not a magic method, just here for example.  */
    public function getHidden() {
        return $this->hidden;
    }
}


echo "<pre>\n";

$obj = new PropertyTest;

$obj->a = 1;
echo $obj->a . "\n\n";

var_dump(isset($obj->a));
unset($obj->a);
var_dump(isset($obj->a));
echo "\n";

echo $obj->declared . "\n\n";

echo "Let's experiment with the private property named 'hidden':\n";
echo "Privates are visible inside the class, so __get() not used...\n";
echo $obj->getHidden() . "\n";
echo "Privates not visible outside of class, so __get() is used...\n";
echo $obj->hidden . "\n";
?>

The above example will output:

Setting 'a' to '1'
Getting 'a'
1

Is 'a' set?
bool(true)
Unsetting 'a'
Is 'a' set?
bool(false)

1

Let's experiment with the private property named 'hidden':
Privates are visible inside the class, so __get() not used...
2
Privates not visible outside of class, so __get() is used...
Getting 'hidden'


Notice:  Undefined property via __get(): hidden in <file> on line 70 in <file> on line 29

Method overloading
mixed __call ( string $name , array $arguments )
mixed __callStatic ( string $name , array $arguments )

__call() is triggered when invoking inaccessible methods in an object context.

__callStatic() is triggered when invoking inaccessible methods in a static context.

The $name argument is the name of the method being called. The $arguments argument is an enumerated array containing the parameters passed to the $name'ed method.

Example #2 Overloading methods via the __call() and __callStatic() methods
<?php
class MethodTest {
    public function __call($name, $arguments) {
        // Note: value of $name is case sensitive.
        echo "Calling object method '$name' "
             . implode(', ', $arguments). "\n";
    }

    /**  As of PHP 5.3.0  */
    public static function __callStatic($name, $arguments) {
        // Note: value of $name is case sensitive.
        echo "Calling static method '$name' "
             . implode(', ', $arguments). "\n";
    }
}

$obj = new MethodTest;
$obj->runTest('in object context');

MethodTest::runTest('in static context');  // As of PHP 5.3.0
?>

The above example will output:

Calling object method 'runTest' in object context
Calling static method 'runTest' in static context

=====================================================================


Object Iteration

PHP 5 provides a way for objects to be defined so it is possible to iterate through a list of items, with, for example a foreach statement. By default, all visible properties will be used for the iteration.

Example #1 Simple Object Iteration
<?php
class MyClass
{
    public $var1 = 'value 1';
    public $var2 = 'value 2';
    public $var3 = 'value 3';

    protected $protected = 'protected var';
    private   $private   = 'private var';

    function iterateVisible() {
       echo "MyClass::iterateVisible:\n";
       foreach($this as $key => $value) {
           print "$key => $value\n";
       }
    }
}

$class = new MyClass();

foreach($class as $key => $value) {
    print "$key => $value\n";
}
echo "\n";


$class->iterateVisible();

?>

The above example will output:

var1 => value 1
var2 => value 2
var3 => value 3

MyClass::iterateVisible:
var1 => value 1
var2 => value 2
var3 => value 3
protected => protected var
private => private var

As the output shows, the foreach iterated through all visible variables that can be accessed. To take it a step further you can implement one of PHP 5's internal interface named Iterator. This allows the object to decide what and how the object will be iterated.

Example #2 Object Iteration implementing Iterator
<?php
class MyIterator implements Iterator
{
    private $var = array();

    public function __construct($array)
    {
        if (is_array($array)) {
            $this->var = $array;
        }
    }

    public function rewind()
    {
        echo "rewinding\n";
        reset($this->var);
    }
  
    public function current()
    {
        $var = current($this->var);
        echo "current: $var\n";
        return $var;
    }
  
    public function key() 
    {
        $var = key($this->var);
        echo "key: $var\n";
        return $var;
    }
  
    public function next() 
    {
        $var = next($this->var);
        echo "next: $var\n";
        return $var;
    }
  
    public function valid()
    {
        $key = key($this->var);
        $var = ($key !== NULL && $key !== FALSE);
        echo "valid: $var\n";
        return $var;
    }

}

$values = array(1,2,3);
$it = new MyIterator($values);

foreach ($it as $a => $b) {
    print "$a: $b\n";
}
?>

The above example will output:

rewinding
valid: 1
current: 1
key: 0
0: 1
next: 2
valid: 1
current: 2
key: 1
1: 2
next: 3
valid: 1
current: 3
key: 2
2: 3
next:
valid: 

You can also define your class so that it doesn't have to define all the Iterator functions by simply implementing the PHP 5 IteratorAggregate interface.

Example #3 Object Iteration implementing IteratorAggregate
<?php
class MyCollection implements IteratorAggregate
{
    private $items = array();
    private $count = 0;

    // Required definition of interface IteratorAggregate
    public function getIterator() {
        return new MyIterator($this->items);
    }

    public function add($value) {
        $this->items[$this->count++] = $value;
    }
}

$coll = new MyCollection();
$coll->add('value 1');
$coll->add('value 2');
$coll->add('value 3');

foreach ($coll as $key => $val) {
    echo "key/value: [$key -> $val]\n\n";
}
?>

The above example will output:

rewinding
current: value 1
valid: 1
current: value 1
key: 0
key/value: [0 -> value 1]

next: value 2
current: value 2
valid: 1
current: value 2
key: 1
key/value: [1 -> value 2]

next: value 3
current: value 3
valid: 1
current: value 3
key: 2
key/value: [2 -> value 3]

next:
current:
valid:

Note:
  For more examples of iterators, see the SPL Extension.

=====================================================================


Patterns

Patterns are ways to describe best practices and good designs. They show a flexible solution to common programming problems.
Factory

The Factory pattern allows for the instantiation of objects at runtime. It is called a Factory Pattern since it is responsible for "manufacturing" an object. A Parameterized Factory receives the name of the class to instantiate as argument.

Example #1 Parameterized Factory Method
<?php
class Example
{
    // The parameterized factory method
    public static function factory($type)
    {
        if (include_once 'Drivers/' . $type . '.php') {
            $classname = 'Driver_' . $type;
            return new $classname;
        } else {
            throw new Exception('Driver not found');
        }
    }
}
?>

Defining this method in a class allows drivers to be loaded on the fly. If the Example class was a database abstraction class, loading a MySQL and SQLite driver could be done as follows:
<?php
// Load a MySQL Driver
$mysql = Example::factory('MySQL');

// Load an SQLite Driver
$sqlite = Example::factory('SQLite');
?>
Singleton

The Singleton ensures that there can be only one instance of a Class and provides a global access point to that instance. Singleton is a "Gang of Four" Creational Pattern.

The Singleton pattern is often implemented in Database Classes, Loggers, Front Controllers or Request and Response objects.

Example #2 Singleton example
<?php
class Example
{
    private static $instance;
    private $count = 0;

    private function __construct()
    {
    }

    public static function singleton()
    {
        if (!isset(self::$instance)) {
            echo 'Creating new instance.';
            $className = __CLASS__;
            self::$instance = new $className;
        }
        return self::$instance;
    }

    public function increment()
    {
        return $this->count++;
    }

    public function __clone()
    {
        trigger_error('Clone is not allowed.', E_USER_ERROR);
    }

    public function __wakeup()
    {
        trigger_error('Unserializing is not allowed.', E_USER_ERROR);
    }
}
?>

Illustrated below is how the Singleton behaves
<?php
$singleton = Example::singleton(); // prints "Creating new instance."
echo $singleton->increment(); // 0
echo $singleton->increment(); // 1

$singleton = Example::singleton(); // reuses existing instance now
echo $singleton->increment(); // 2
echo $singleton->increment(); // 3

// all of these will raise a Fatal Error
$singleton2 = new Example;
$singleton3 = clone $singleton;
$singleton4 = unserialize(serialize($singleton));
?>
Warning

The Singleton pattern is one of the more controversial patterns. Critics argue that Singletons introduce Global State into an application and tightly couple the Singleton and its consuming classes. This leads to hidden dependencies and unexpected side-effects, which in turn leads to code that is harder to test and maintain.

Critics further argue that it is pointless to use a Singleton in a Shared Nothing Architecture like PHP where objects are unique within the Request only anyways. It is easier and cleaner to create collaborator object graphs by using Builders and Factory patterns once at the beginning of the Request.

Singletons also violate several of the "SOLID" OOP design principles and the Law of Demeter. Singletons cannot be serialized. They cannot be subtyped (before PHP 5.3) and won't be Garbage Collected because of the instance being stored as a static attribute of the Singleton.

=====================================================================


Magic Methods

The function names __construct, __destruct, __call, __callStatic, __get, __set, __isset, __unset, __sleep, __wakeup, __toString, __invoke, __set_state and __clone are magical in PHP classes. You cannot have functions with these names in any of your classes unless you want the magic functionality associated with them.
Caution

PHP reserves all function names starting with __ as magical. It is recommended that you do not use function names with __ in PHP unless you want some documented magic functionality.
__sleep and __wakeup

serialize() checks if your class has a function with the magic name __sleep. If so, that function is executed prior to any serialization. It can clean up the object and is supposed to return an array with the names of all variables of that object that should be serialized. If the method doesn't return anything then NULL is serialized and E_NOTICE is issued.

    Note:

    It is not possible for __sleep to return names of private properties in parent classes. Doing this will result in an E_NOTICE level error. Instead you may use the Serializable interface.

The intended use of __sleep is to commit pending data or perform similar cleanup tasks. Also, the function is useful if you have very large objects which do not need to be saved completely.

Conversely, unserialize() checks for the presence of a function with the magic name __wakeup. If present, this function can reconstruct any resources that the object may have.

The intended use of __wakeup is to reestablish any database connections that may have been lost during serialization and perform other reinitialization tasks.

Example #1 Sleep and wakeup
<?php
class Connection
{
    protected $link;
    private $server, $username, $password, $db;
    
    public function __construct($server, $username, $password, $db)
    {
        $this->server = $server;
        $this->username = $username;
        $this->password = $password;
        $this->db = $db;
        $this->connect();
    }
    
    private function connect()
    {
        $this->link = mysql_connect($this->server, $this->username, $this->password);
        mysql_select_db($this->db, $this->link);
    }
    
    public function __sleep()
    {
        return array('server', 'username', 'password', 'db');
    }
    
    public function __wakeup()
    {
        $this->connect();
    }
}
?>
__toString

The __toString method allows a class to decide how it will react when it is treated like a string. For example, what echo $obj; will print. This method must return a string, as otherwise a fatal E_RECOVERABLE_ERROR level error is emitted.

Example #2 Simple example
<?php
// Declare a simple class
class TestClass
{
    public $foo;

    public function __construct($foo)
    {
        $this->foo = $foo;
    }

    public function __toString()
    {
        return $this->foo;
    }
}

$class = new TestClass('Hello');
echo $class;
?>

The above example will output:

Hello

It is worth noting that before PHP 5.2.0 the __toString method was only called when it was directly combined with echo() or print(). Since PHP 5.2.0, it is called in any string context (e.g. in printf() with %s modifier) but not in other types contexts (e.g. with %d modifier). Since PHP 5.2.0, converting objects without __toString method to string would cause E_RECOVERABLE_ERROR.
__invoke

The __invoke method is called when a script tries to call an object as a function.

    Note:

    This feature is available since PHP 5.3.0.

Example #3 Using __invoke
<?php
class CallableClass
{
    public function __invoke($x)
    {
        var_dump($x);
    }
}
$obj = new CallableClass;
$obj(5);
var_dump(is_callable($obj));
?>

The above example will output:

int(5)
bool(true)

__set_state

This static method is called for classes exported by var_export() since PHP 5.1.0.

The only parameter of this method is an array containing exported properties in the form array('property' => value, ...).

Example #4 Using __set_state (since PHP 5.1.0)
<?php

class A
{
    public $var1;
    public $var2;

    public static function __set_state($an_array) // As of PHP 5.1.0
    {
        $obj = new A;
        $obj->var1 = $an_array['var1'];
        $obj->var2 = $an_array['var2'];
        return $obj;
    }
}

$a = new A;
$a->var1 = 5;
$a->var2 = 'foo';

eval('$b = ' . var_export($a, true) . ';'); // $b = A::__set_state(array(
                                            //    'var1' => 5,
                                            //    'var2' => 'foo',
                                            // ));
var_dump($b);

?>

The above example will output:

object(A)#2 (2) {
  ["var1"]=>
  int(5)
  ["var2"]=>
  string(3) "foo"
}

=====================================================================


Final Keyword

PHP 5 introduces the final keyword, which prevents child classes from overriding a method by prefixing the definition with final. If the class itself is being defined final then it cannot be extended.

Example #1 Final methods example
<?php
class BaseClass {
   public function test() {
       echo "BaseClass::test() called\n";
   }
   
   final public function moreTesting() {
       echo "BaseClass::moreTesting() called\n";
   }
}

class ChildClass extends BaseClass {
   public function moreTesting() {
       echo "ChildClass::moreTesting() called\n";
   }
}
// Results in Fatal error: Cannot override final method BaseClass::moreTesting()
?>

Example #2 Final class example
<?php
final class BaseClass {
   public function test() {
       echo "BaseClass::test() called\n";
   }

   // Here it doesn't matter if you specify the function as final or not
   final public function moreTesting() {
       echo "BaseClass::moreTesting() called\n";
   }
}

class ChildClass extends BaseClass {
}
// Results in Fatal error: Class ChildClass may not inherit from final class (BaseClass)
?>

    Note: Properties cannot be declared final, only classes and methods may be declared as final. 

=====================================================================


Object Cloning

Creating a copy of an object with fully replicated properties is not always the wanted behavior. A good example of the need for copy constructors, is if you have an object which represents a GTK window and the object holds the resource of this GTK window, when you create a duplicate you might want to create a new window with the same properties and have the new object hold the resource of the new window. Another example is if your object holds a reference to another object which it uses and when you replicate the parent object you want to create a new instance of this other object so that the replica has its own separate copy.

An object copy is created by using the clone keyword (which calls the object's __clone() method if possible). An object's __clone() method cannot be called directly.

$copy_of_object = clone $object;

When an object is cloned, PHP 5 will perform a shallow copy of all of the object's properties. Any properties that are references to other variables, will remain references.

Once the cloning is complete, if a __clone() method is defined, then the newly created object's __clone() method will be called, to allow any necessary properties that need to be changed.

Example #1 Cloning an object
<?php
class SubObject
{
    static $instances = 0;
    public $instance;

    public function __construct() {
        $this->instance = ++self::$instances;
    }

    public function __clone() {
        $this->instance = ++self::$instances;
    }
}

class MyCloneable
{
    public $object1;
    public $object2;

    function __clone()
    {
        // Force a copy of this->object, otherwise
        // it will point to same object.
        $this->object1 = clone $this->object1;
    }
}

$obj = new MyCloneable();

$obj->object1 = new SubObject();
$obj->object2 = new SubObject();

$obj2 = clone $obj;


print("Original Object:\n");
print_r($obj);

print("Cloned Object:\n");
print_r($obj2);

?>

The above example will output:

Original Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 1
        )

    [object2] => SubObject Object
        (
            [instance] => 2
        )

)
Cloned Object:
MyCloneable Object
(
    [object1] => SubObject Object
        (
            [instance] => 3
        )

    [object2] => SubObject Object
        (
            [instance] => 2
        )

)

=====================================================================


Comparing Objects

In PHP 5, object comparison is more complicated than in PHP 4 and more in accordance to what one will expect from an Object Oriented Language (not that PHP 5 is such a language).

When using the comparison operator (==), object variables are compared in a simple manner, namely: Two object instances are equal if they have the same attributes and values, and are instances of the same class.

On the other hand, when using the identity operator (===), object variables are identical if and only if they refer to the same instance of the same class.

An example will clarify these rules.

Example #1 Example of object comparison in PHP 5
<?php
function bool2str($bool)
{
    if ($bool === false) {
        return 'FALSE';
    } else {
        return 'TRUE';
    }
}

function compareObjects(&$o1, &$o2)
{
    echo 'o1 == o2 : ' . bool2str($o1 == $o2) . "\n";
    echo 'o1 != o2 : ' . bool2str($o1 != $o2) . "\n";
    echo 'o1 === o2 : ' . bool2str($o1 === $o2) . "\n";
    echo 'o1 !== o2 : ' . bool2str($o1 !== $o2) . "\n";
}

class Flag
{
    public $flag;

    function Flag($flag = true) {
        $this->flag = $flag;
    }
}

class OtherFlag
{
    public $flag;

    function OtherFlag($flag = true) {
        $this->flag = $flag;
    }
}

$o = new Flag();
$p = new Flag();
$q = $o;
$r = new OtherFlag();

echo "Two instances of the same class\n";
compareObjects($o, $p);

echo "\nTwo references to the same instance\n";
compareObjects($o, $q);

echo "\nInstances of two different classes\n";
compareObjects($o, $r);
?>

The above example will output:

Two instances of the same class
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : FALSE
o1 !== o2 : TRUE

Two references to the same instance
o1 == o2 : TRUE
o1 != o2 : FALSE
o1 === o2 : TRUE
o1 !== o2 : FALSE

Instances of two different classes
o1 == o2 : FALSE
o1 != o2 : TRUE
o1 === o2 : FALSE
o1 !== o2 : TRUE

    Note:

    Extensions can define own rules for their objects comparison.

=====================================================================


Type Hinting

PHP 5 introduces Type Hinting. Functions are now able to force parameters to be objects (by specifying the name of the class in the function prototype) or arrays (since PHP 5.1). However, if NULL is used as the default parameter value, it will be allowed as an argument for any later call.

Example #1 Type Hinting examples
<?php
// An example class
class MyClass
{
    /**
     * A test function
     *
     * First parameter must be an object of type OtherClass
     */
    public function test(OtherClass $otherclass) {
        echo $otherclass->var;
    }


    /**
     * Another test function
     *
     * First parameter must be an array
     */
    public function test_array(array $input_array) {
        print_r($input_array);
    }
}

// Another example class
class OtherClass {
    public $var = 'Hello World';
}
?>

Failing to satisfy the type hint results in a catchable fatal error.
<?php
// An instance of each class
$myclass = new MyClass;
$otherclass = new OtherClass;

// Fatal Error: Argument 1 must be an object of class OtherClass
$myclass->test('hello');

// Fatal Error: Argument 1 must be an instance of OtherClass
$foo = new stdClass;
$myclass->test($foo);

// Fatal Error: Argument 1 must not be null
$myclass->test(null);

// Works: Prints Hello World
$myclass->test($otherclass);

// Fatal Error: Argument 1 must be an array
$myclass->test_array('a string');

// Works: Prints the array
$myclass->test_array(array('a', 'b', 'c'));
?>

Type hinting also works with functions:
<?php
// An example class
class MyClass {
    public $var = 'Hello World';
}

/**
 * A test function
 *
 * First parameter must be an object of type MyClass
 */
function MyFunction (MyClass $foo) {
    echo $foo->var;
}

// Works
$myclass = new MyClass;
MyFunction($myclass);
?>

Type hinting allowing NULL value:
<?php

/* Accepting NULL value */
function test(stdClass $obj = NULL) {

}

test(NULL);
test(new stdClass);

?>

Type Hints can only be of the object and array (since PHP 5.1) type. Traditional type hinting with int and string isn't supported.

=====================================================================


Late Static Bindings

As of PHP 5.3.0, PHP implements a feature called late static bindings which can be used to reference the called class in a context of static inheritance.

More precisely, late static bindings work by storing the class named in the last "non-forwarding call". In case of static method calls, this is the class explicitly named (usually the one on the left of the :: operator); in case of non static method calls, it is the class of the object. A "forwarding call" is a static one that is introduced by self::, parent::, static::, or, if going up in the class hierarchy, forward_static_call(). The function get_called_class() can be used to retrieve a string with the name of the called class and static:: introduces its scope.

This feature was named "late static bindings" with an internal perspective in mind. "Late binding" comes from the fact that static:: will not be resolved using the class where the method is defined but it will rather be computed using runtime information. It was also called a "static binding" as it can be used for (but is not limited to) static method calls.
Limitations of self::

Static references to the current class like self:: or __CLASS__ are resolved using the class in which the function belongs, as in where it was defined:

Example #1 self:: usage
<?php
class A {
    public static function who() {
        echo __CLASS__;
    }
    public static function test() {
        self::who();
    }
}

class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test();
?>

The above example will output:

A

Late Static Bindings' usage

Late static bindings tries to solve that limitation by introducing a keyword that references the class that was initially called at runtime. Basically, a keyword that would allow you to reference B from test() in the previous example. It was decided not to introduce a new keyword but rather use static that was already reserved.

Example #2 static:: simple usage
<?php
class A {
    public static function who() {
        echo __CLASS__;
    }
    public static function test() {
        static::who(); // Here comes Late Static Bindings
    }
}

class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test();
?>

The above example will output:

B

    Note:

    In non-static contexts, the called class will be the class of the object instance. Since $this-> will try to call private methods from the same scope, using static:: may give different results. Another difference is that static:: can only refer to static properties.

Example #3 static:: usage in a non-static context
<?php
class A {
    private function foo() {
        echo "success!\n";
    }
    public function test() {
        $this->foo();
        static::foo();
    }
}

class B extends A {
   /* foo() will be copied to B, hence its scope will still be A and
    * the call be successful */
}

class C extends A {
    private function foo() {
        /* original method is replaced; the scope of the new one is C */
    }
}

$b = new B();
$b->test();
$c = new C();
$c->test();   //fails
?>

The above example will output:

success!
success!
success!


Fatal error:  Call to private method C::foo() from context 'A' in /tmp/test.php on line 9

    Note:

    Late static bindings' resolution will stop at a fully resolved static call with no fallback. On the other hand, static calls using keywords like parent:: or self:: will forward the calling information.

    Example #4 Forwarding and non-forwarding calls
    <?php
    class A {
        public static function foo() {
            static::who();
        }

        public static function who() {
            echo __CLASS__."\n";
        }
    }

    class B extends A {
        public static function test() {
            A::foo();
            parent::foo();
            self::foo();
        }

        public static function who() {
            echo __CLASS__."\n";
        }
    }
    class C extends B {
        public static function who() {
            echo __CLASS__."\n";
        }
    }

    C::test();
    ?>

    The above example will output:

    A
    C
    C

=====================================================================


Objects and references

One of the key-points of PHP5 OOP that is often mentioned is that "objects are passed by references by default". This is not completely true. This section rectifies that general thought using some examples.

A PHP reference is an alias, which allows two different variables to write to the same value. As of PHP5, an object variable doesn't contain the object itself as value anymore. It only contains an object identifier which allows object accessors to find the actual object. When an object is sent by argument, returned or assigned to another variable, the different variables are not aliases: they hold a copy of the identifier, which points to the same object.

Example #1 References and Objects
<?php
class A {
    public $foo = 1;
}  

$a = new A;
$b = $a;     // $a and $b are copies of the same identifier
             // ($a) = ($b) = <id>
$b->foo = 2;
echo $a->foo."\n";


$c = new A;
$d = &$c;    // $c and $d are references
             // ($c,$d) = <id>

$d->foo = 2;
echo $c->foo."\n";


$e = new A;

function foo($obj) {
    // ($obj) = ($e) = <id>
    $obj->foo = 2;
}

foo($e);
echo $e->foo."\n";

?>

The above example will output:

2
2
2

=====================================================================


Object Serialization
Serializing objects - objects in sessions

serialize() returns a string containing a byte-stream representation of any value that can be stored in PHP. unserialize() can use this string to recreate the original variable values. Using serialize to save an object will save all variables in an object. The methods in an object will not be saved, only the name of the class.

In order to be able to unserialize() an object, the class of that object needs to be defined. That is, if you have an object of class A and serialize this, you'll get a string that refers to class A and contains all values of variables contained in it. If you want to be able to unserialize this in another file, an object of class A, the definition of class A must be present in that file first. This can be done for example by storing the class definition of class A in an include file and including this file or making use of the spl_autoload_register() function.
<?php
// classa.inc:
  
  class A {
      public $one = 1;
    
      public function show_one() {
          echo $this->one;
      }
  }
  
// page1.php:

  include("classa.inc");
  
  $a = new A;
  $s = serialize($a);
  // store $s somewhere where page2.php can find it.
  file_put_contents('store', $s);

// page2.php:
  
  // this is needed for the unserialize to work properly.
  include("classa.inc");

  $s = file_get_contents('store');
  $a = unserialize($s);

  // now use the function show_one() of the $a object.  
  $a->show_one();
?>

If an application is using sessions and uses session_register() to register objects, these objects are serialized automatically at the end of each PHP page, and are unserialized automatically on each of the following pages. This means that these objects can show up on any of the application's pages once they become part of the session. However, the session_register() is removed since PHP 5.4.0.

It is strongly recommended that if an application serializes objects, for use later in the application, that the application include the class definition for that object throughout the application. Not doing so might result in an object being unserialized without a class definition, which will result in PHP giving the object a class of __PHP_Incomplete_Class_Name, which has no methods and would render the object useless.

So if in the example above $a became part of a session by running session_register("a"), you should include the file classa.inc on all of your pages, not only page1.php and page2.php.

=====================================================================

OOP Changelog

Changes to the PHP 5 OOP model are logged here. Descriptions and other notes regarding these features are documented within the OOP 5 documentation.

Version 	Description
5.3.3 	Changed: Methods with the same name as the last element of a namespaced class name will no longer be treated as constructor. This change doesn't affect non-namespaced classes.
5.3.0 	Changed: Classes that implement interfaces with methods that have default values in the prototype are no longer required to match the interface's default value.
5.3.0 	Changed: It's now possible to reference the class using a variable (e.g., echo $classname::constant;). The variable's value can not be a keyword (e.g., self, parent or static).
5.3.0 	Changed: An E_WARNING level error is issued if the magic overloading methods are declared static. It also enforces the public visibility requirement.
5.3.0 	Changed: Prior to 5.3.0, exceptions thrown in the __autoload function could not be caught in the catch block, and would result in a fatal error. Exceptions now thrown in the __autoload function can be caught in the catch block, with one proviso. If throwing a custom exception, then the custom exception class must be available. The __autoload function may be used recursively to autoload the custom exception class.
5.3.0 	Added: The __callStatic method.
5.3.0 	Added: heredoc and nowdoc support for class const and property definitions. Note: heredoc values must follow the same rules as double-quoted strings, (e.g., no variables within).
5.3.0 	Added: Late Static Bindings.
5.3.0 	Added: The __invoke method.
5.2.0 	Changed: The __toString method was only called when it was directly combined with echo() or print(). But now, it is called in any string context (e.g. in printf() with %s modifier) but not in other types contexts (e.g. with %d modifier). Since PHP 5.2.0, converting objects without a __toString method to string emits a E_RECOVERABLE_ERROR level error.
5.1.3 	Changed: In previous versions of PHP 5, the use of var was considered deprecated and would issue an E_STRICT level error. It's no longer deprecated, therefore does not emit the error.
5.1.0 	Changed: The __set_state static method is now called for classes exported by var_export().
5.1.0 	Added: The __isset and __unset methods. 

=====================================================================
=====================================================================
    * Namespaces
=====================================================================

Table of Contents

    * Namespaces overview
    * Defining namespaces
    * Declaring sub-namespaces
    * Defining multiple namespaces in the same file
    * Using namespaces: Basics
    * Namespaces and dynamic language features
    * namespace keyword and __NAMESPACE__ constant
    * Using namespaces: Aliasing/Importing
    * Global space
    * Using namespaces: fallback to global function/constant
    * Name resolution rules
    * FAQ: things you need to know about namespaces

=====================================================================


Namespaces overview

What are namespaces? In the broadest definition namespaces are a way of encapsulating items. This can be seen as an abstract concept in many places. For example, in any operating system directories serve to group related files, and act as a namespace for the files within them. As a concrete example, the file foo.txt can exist in both directory /home/greg and in /home/other, but two copies of foo.txt cannot co-exist in the same directory. In addition, to access the foo.txt file outside of the /home/greg directory, we must prepend the directory name to the file name using the directory separator to get /home/greg/foo.txt. This same principle extends to namespaces in the programming world.

In the PHP world, namespaces are designed to solve two problems that authors of libraries and applications encounter when creating re-usable code elements such as classes or functions:

   1. Name collisions between code you create, and internal PHP classes/functions/constants or third-party classes/functions/constants.
   2. Ability to alias (or shorten) Extra_Long_Names designed to alleviate the first problem, improving readability of source code.

PHP Namespaces provide a way in which to group related classes, functions and constants. Here is an example of namespace syntax in PHP:

Example #1 Namespace syntax example
<?php
namespace my\name; // see "Defining Namespaces" section

class MyClass {}
function myfunction() {}
const MYCONST = 1;

$a = new MyClass;
$c = new \my\name\MyClass; // see "Global Space" section

$a = strlen('hi'); // see "Using namespaces: fallback to global
                   // function/constant" section

$d = namespace\MYCONST; // see "namespace operator and __NAMESPACE__
                        // constant" section
$d = __NAMESPACE__ . '\MYCONST';
echo constant($d); // see "Namespaces and dynamic language features" section
?>

=====================================================================


Defining namespaces

Although any valid PHP code can be contained within a namespace, only three type of code are affected by namespaces: classes, functions and constants.

Namespaces are declared using the namespace keyword. A file containing a namespace must declare the namespace at the top of the file before any other code - with one exception: the declare keyword.

Example #1 Declaring a single namespace
<?php
namespace MyProject;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }

?>
The only code construct allowed before a namespace declaration is the declare statement, for defining encoding of a source file. In addition, no non-PHP code may precede a namespace declaration, including extra whitespace:

Example #2 Declaring a single namespace
<html>
<?php
namespace MyProject; // fatal error - namespace must be the first statement in the script
?>

In addition, unlike any other PHP construct, the same namespace may be defined in multiple files, allowing splitting up of a namespace's contents across the filesystem.

=====================================================================

Declaring sub-namespaces

Much like directories and files, PHP namespaces also contain the ability to specify a hierarchy of namespace names. Thus, a namespace name can be defined with sub-levels:

Example #1 Declaring a single namespace with hierarchy
<?php
namespace MyProject\Sub\Level;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }

?>
The above example creates constant MyProject\Sub\Level\CONNECT_OK, class MyProject\Sub\Level\Connection and function MyProject\Sub\Level\connect. 

=====================================================================


Defining multiple namespaces in the same file

Multiple namespaces may also be declared in the same file. There are two allowed syntaxes.

Example #1 Declaring multiple namespaces, simple combination syntax
<?php
namespace MyProject;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }

namespace AnotherProject;

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
?>

This syntax is not recommended for combining namespaces into a single file. Instead it is recommended to use the alternate bracketed syntax.

Example #2 Declaring multiple namespaces, bracketed syntax
<?php
namespace MyProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}

namespace AnotherProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}
?>

It is strongly discouraged as a coding practice to combine multiple namespaces into the same file. The primary use case is to combine multiple PHP scripts into the same file.

To combine global non-namespaced code with namespaced code, only bracketed syntax is supported. Global code should be encased in a namespace statement with no namespace name as in:

Example #3 Declaring multiple namespaces and unnamespaced code
<?php
namespace MyProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}

namespace { // global code
session_start();
$a = MyProject\connect();
echo MyProject\Connection::start();
}
?>

No PHP code may exist outside of the namespace brackets except for an opening declare statement.

Example #4 Declaring multiple namespaces and unnamespaced code
<?php
declare(encoding='UTF-8');
namespace MyProject {

const CONNECT_OK = 1;
class Connection { /* ... */ }
function connect() { /* ... */  }
}

namespace { // global code
session_start();
$a = MyProject\connect();
echo MyProject\Connection::start();
}
?>

=====================================================================


Using namespaces: Basics

Before discussing the use of namespaces, it is important to understand how PHP knows which namespaced element your code is requesting. A simple analogy can be made between PHP namespaces and a filesystem. There are three ways to access a file in a file system:

   1. Relative file name like foo.txt. This resolves to currentdirectory/foo.txt where currentdirectory is the directory currently occupied. So if the current directory is /home/foo, the name resolves to /home/foo/foo.txt.
   2. Relative path name like subdirectory/foo.txt. This resolves to currentdirectory/subdirectory/foo.txt.
   3. Absolute path name like /main/foo.txt. This resolves to /main/foo.txt.

The same principle can be applied to namespaced elements in PHP. For example, a class name can be referred to in three ways:

   1. Unqualified name, or an unprefixed class name like $a = new foo(); or foo::staticmethod();. If the current namespace is currentnamespace, this resolves to currentnamespace\foo. If the code is global, non-namespaced code, this resolves to foo. One caveat: unqualified names for functions and constants will resolve to global functions and constants if the namespaced function or constant is not defined. See Using namespaces: fallback to global function/constant for details.
   2. Qualified name, or a prefixed class name like $a = new subnamespace\foo(); or subnamespace\foo::staticmethod();. If the current namespace is currentnamespace, this resolves to currentnamespace\subnamespace\foo. If the code is global, non-namespaced code, this resolves to subnamespace\foo.
   3. Fully qualified name, or a prefixed name with global prefix operator like $a = new \currentnamespace\foo(); or \currentnamespace\foo::staticmethod();. This always resolves to the literal name specified in the code, currentnamespace\foo.

Here is an example of the three kinds of syntax in actual code:

file1.php
<?php
namespace Foo\Bar\subnamespace;

const FOO = 1;
function foo() {}
class foo
{
    static function staticmethod() {}
}
?>

file2.php
<?php
namespace Foo\Bar;
include 'file1.php';

const FOO = 2;
function foo() {}
class foo
{
    static function staticmethod() {}
}

/* Unqualified name */
foo(); // resolves to function Foo\Bar\foo
foo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethod
echo FOO; // resolves to constant Foo\Bar\FOO

/* Qualified name */
subnamespace\foo(); // resolves to function Foo\Bar\subnamespace\foo
subnamespace\foo::staticmethod(); // resolves to class Foo\Bar\subnamespace\foo,
                                  // method staticmethod
echo subnamespace\FOO; // resolves to constant Foo\Bar\subnamespace\FOO
                                  
/* Fully qualified name */
\Foo\Bar\foo(); // resolves to function Foo\Bar\foo
\Foo\Bar\foo::staticmethod(); // resolves to class Foo\Bar\foo, method staticmethod
echo \Foo\Bar\FOO; // resolves to constant Foo\Bar\FOO
?>

Note that to access any global class, function or constant, a fully qualified name can be used, such as \strlen() or \Exception or \INI_ALL.

Example #1 Accessing global classes, functions and constants from within a namespace
<?php
namespace Foo;

function strlen() {}
const INI_ALL = 3;
class Exception {}

$a = \strlen('hi'); // calls global function strlen
$b = \INI_ALL; // accesses global constant INI_ALL
$c = new \Exception('error'); // instantiates global class Exception
?>

=====================================================================


Namespaces and dynamic language features

PHP's implementation of namespaces is influenced by its dynamic nature as a programming language. Thus, to convert code like the following example into namespaced code:

Example #1 Dynamically accessing elements

example1.php:
<?php
class classname
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function funcname()
{
    echo __FUNCTION__,"\n";
}
const constname = "global";

$a = 'classname';
$obj = new $a; // prints classname::__construct
$b = 'funcname';
$b(); // prints funcname
echo constant('constname'), "\n"; // prints global
?>
One must use the fully qualified name (class name with namespace prefix). Note that because there is no difference between a qualified and a fully qualified Name inside a dynamic class name, function name, or constant name, the leading backslash is not necessary.

Example #2 Dynamically accessing namespaced elements
<?php
namespace namespacename;
class classname
{
    function __construct()
    {
        echo __METHOD__,"\n";
    }
}
function funcname()
{
    echo __FUNCTION__,"\n";
}
const constname = "namespaced";

include 'example1.php';

$a = 'classname';
$obj = new $a; // prints classname::__construct
$b = 'funcname';
$b(); // prints funcname
echo constant('constname'), "\n"; // prints global

/* note that if using double quotes, "\\namespacename\\classname" must be used */
$a = '\namespacename\classname';
$obj = new $a; // prints namespacename\classname::__construct
$a = 'namespacename\classname';
$obj = new $a; // also prints namespacename\classname::__construct
$b = 'namespacename\funcname';
$b(); // prints namespacename\funcname
$b = '\namespacename\funcname';
$b(); // also prints namespacename\funcname
echo constant('\namespacename\constname'), "\n"; // prints namespaced
echo constant('namespacename\constname'), "\n"; // also prints namespaced
?>

Be sure to read the note about escaping namespace names in strings.

=====================================================================


namespace keyword and __NAMESPACE__ constant

PHP supports two ways of abstractly accessing elements within the current namespace, the __NAMESPACE__ magic constant, and the namespace keyword.

The value of __NAMESPACE__ is a string that contains the current namespace name. In global, un-namespaced code, it contains an empty string.

Example #1 __NAMESPACE__ example, namespaced code
<?php
namespace MyProject;

echo '"', __NAMESPACE__, '"'; // outputs "MyProject"
?>

Example #2 __NAMESPACE__ example, global code
<?php

echo '"', __NAMESPACE__, '"'; // outputs ""
?>
The __NAMESPACE__ constant is useful for dynamically constructing names, for instance:

Example #3 using __NAMESPACE__ for dynamic name construction
<?php
namespace MyProject;

function get($classname)
{
    $a = __NAMESPACE__ . '\\' . $classname;
    return new $a;
}
?>

The namespace keyword can be used to explicitly request an element from the current namespace or a sub-namespace. It is the namespace equivalent of the self operator for classes.

Example #4 the namespace operator, inside a namespace
<?php
namespace MyProject;

use blah\blah as mine; // see "Using namespaces: importing/aliasing"

blah\mine(); // calls function MyProject\blah\mine()
namespace\blah\mine(); // calls function MyProject\blah\mine()

namespace\func(); // calls function MyProject\func()
namespace\sub\func(); // calls function MyProject\sub\func()
namespace\cname::method(); // calls static method "method" of class MyProject\cname
$a = new namespace\sub\cname(); // instantiates object of class MyProject\sub\cname
$b = namespace\CONSTANT; // assigns value of constant MyProject\CONSTANT to $b
?>

Example #5 the namespace operator, in global code
<?php

namespace\func(); // calls function func()
namespace\sub\func(); // calls function sub\func()
namespace\cname::method(); // calls static method "method" of class cname
$a = new namespace\sub\cname(); // instantiates object of class sub\cname
$b = namespace\CONSTANT; // assigns value of constant CONSTANT to $b
?>

=====================================================================


Using namespaces: Aliasing/Importing

The ability to refer to an external fully qualified name with an alias, or importing, is an important feature of namespaces. This is similar to the ability of unix-based filesystems to create symbolic links to a file or to a directory.

PHP namespaces support three kinds of aliasing or importing: aliasing a class name, aliasing an interface name, and aliasing a namespace name. Note that importing a function or constant is not supported.

In PHP, aliasing is accomplished with the use operator. Here is an example showing all 3 kinds of importing:

Example #1 importing/aliasing with the use operator
<?php
namespace foo;
use My\Full\Classname as Another;

// this is the same as use My\Full\NSname as NSname
use My\Full\NSname;

// importing a global class
use ArrayObject;

$obj = new namespace\Another; // instantiates object of class foo\Another
$obj = new Another; // instantiates object of class My\Full\Classname
NSname\subns\func(); // calls function My\Full\NSname\subns\func
$a = new ArrayObject(array(1)); // instantiates object of class ArrayObject
// without the "use ArrayObject" we would instantiate an object of class foo\ArrayObject
?>
Note that for namespaced names (fully qualified namespace names containing namespace separator, such as Foo\Bar as opposed to global names that do not, such as FooBar), the leading backslash is unnecessary and not recommended, as import names must be fully qualified, and are not processed relative to the current namespace.

PHP additionally supports a convenience shortcut to place multiple use statements on the same line

Example #2 importing/aliasing with the use operator, multiple use statements combined
<?php
use My\Full\Classname as Another, My\Full\NSname;

$obj = new Another; // instantiates object of class My\Full\Classname
NSname\subns\func(); // calls function My\Full\NSname\subns\func
?>

Importing is performed at compile-time, and so does not affect dynamic class, function or constant names.

Example #3 Importing and dynamic names
<?php
use My\Full\Classname as Another, My\Full\NSname;

$obj = new Another; // instantiates object of class My\Full\Classname
$a = 'Another';
$obj = new $a;      // instantiates object of class Another
?>

In addition, importing only affects unqualified and qualified names. Fully qualified names are absolute, and unaffected by imports.

Example #4 Importing and fully qualified names
<?php
use My\Full\Classname as Another, My\Full\NSname;

$obj = new Another; // instantiates object of class My\Full\Classname
$obj = new \Another; // instantiates object of class Another
$obj = new Another\thing; // instantiates object of class My\Full\Classname\thing
$obj = new \Another\thing; // instantiates object of class Another\thing
?>
Scoping rules for importing

The use keyword must be declared in the outermost scope of a file (the global scope) or inside namespace declarations. This is because the importing is done at compile time and not runtime, so it cannot be block scoped. The following example will show an illegal use of the use keyword:

Example #5 Illegal importing rule
<?php
namespace Languages;

class Greenlandic
{
    use Languages\Danish;

    ...
}
?>

Note:
  Importing rules are per file basis, meaning included files will NOT inherit the parent file's importing rules.

=====================================================================


Global space

Without any namespace definition, all class and function definitions are placed into the global space - as it was in PHP before namespaces were supported. Prefixing a name with \ will specify that the name is required from the global space even in the context of the namespace.

Example #1 Using global space specification
<?php
namespace A\B\C;

/* This function is A\B\C\fopen */
function fopen() { 
     /* ... */
     $f = \fopen(...); // call global fopen
     return $f;
} 
?>

=====================================================================


Using namespaces: fallback to global function/constant

Inside a namespace, when PHP encounters a unqualified Name in a class name, function or constant context, it resolves these with different priorities. Class names always resolve to the current namespace name. Thus to access internal or non-namespaced user classes, One must refer to them with their fully qualified Name as in:

Example #1 Accessing global classes inside a namespace
<?php
namespace A\B\C;
class Exception extends \Exception {}

$a = new Exception('hi'); // $a is an object of class A\B\C\Exception
$b = new \Exception('hi'); // $b is an object of class Exception

$c = new ArrayObject; // fatal error, class A\B\C\ArrayObject not found
?>

For functions and constants, PHP will fall back to global functions or constants if a namespaced function or constant does not exist.

Example #2 global functions/constants fallback inside a namespace
<?php
namespace A\B\C;

const E_ERROR = 45;
function strlen($str)
{
    return \strlen($str) - 1;
}

echo E_ERROR, "\n"; // prints "45"
echo INI_ALL, "\n"; // prints "7" - falls back to global INI_ALL

echo strlen('hi'), "\n"; // prints "1"
if (is_array('hi')) { // prints "is not array"
    echo "is array\n";
} else {
    echo "is not array\n";
}
?>

=====================================================================


Name resolution rules

For the purposes of these resolution rules, here are some important definitions:

Namespace name definitions
Unqualified name

    This is an identifier without a namespace separator, such as Foo
Qualified name

    This is an identifier with a namespace separator, such as Foo\Bar
Fully qualified name

    This is an identifier with a namespace separator that begins with a namespace separator, such as \Foo\Bar. namespace\Foo is also a fully qualified name.

Names are resolved following these resolution rules:

   1. Calls to fully qualified functions, classes or constants are resolved at compile-time. For instance new \A\B resolves to class A\B.
   2. All unqualified and qualified names (not fully qualified names) are translated during compilation according to current import rules. For example, if the namespace A\B\C is imported as C, a call to C\D\e() is translated to A\B\C\D\e().
   3. Inside a namespace, all qualified names not translated according to import rules have the current namespace prepended. For example, if a call to C\D\e() is performed within namespace A\B, it is translated to A\B\C\D\e().
   4. Unqualified class names are translated during compilation according to current import rules (full name substituted for short imported name). In example, if the namespace A\B\C is imported as C, new C() is translated to new A\B\C().
   5. Inside namespace (say A\B), calls to unqualified functions are resolved at run-time. Here is how a call to function foo() is resolved:
         1. It looks for a function from the current namespace: A\B\foo().
         2. It tries to find and call the global function foo().
   6. Inside namespace (say A\B), calls to unqualified or qualified class names (not fully qualified class names) are resolved at run-time. Here is how a call to new C() or new D\E() is resolved. For new C():
         1. It looks for a class from the current namespace: A\B\C.
         2. It attempts to autoload A\B\C.
      For new D\E():
         1. It looks for a class by prepending the current namespace: A\B\D\E.
         2. It attempts to autoload A\B\D\E.
      To reference any global class in the global namespace, its fully qualified name new \C() must be used.

Example #1 Name resolutions illustrated
<?php
namespace A;
use B\D, C\E as F;

// function calls

foo();      // first tries to call "foo" defined in namespace "A"
            // then calls global function "foo"

\foo();     // calls function "foo" defined in global scope

my\foo();   // calls function "foo" defined in namespace "A\my"

F();        // first tries to call "F" defined in namespace "A"
            // then calls global function "F"

// class references

new B();    // creates object of class "B" defined in namespace "A"
            // if not found, it tries to autoload class "A\B"

new D();    // using import rules, creates object of class "D" defined in namespace "B"
            // if not found, it tries to autoload class "B\D"

new F();    // using import rules, creates object of class "E" defined in namespace "C"
            // if not found, it tries to autoload class "C\E"

new \B();   // creates object of class "B" defined in global scope
            // if not found, it tries to autoload class "B"

new \D();   // creates object of class "D" defined in global scope
            // if not found, it tries to autoload class "D"

new \F();   // creates object of class "F" defined in global scope
            // if not found, it tries to autoload class "F"

// static methods/namespace functions from another namespace

B\foo();    // calls function "foo" from namespace "A\B"

B::foo();   // calls method "foo" of class "B" defined in namespace "A"
            // if class "A\B" not found, it tries to autoload class "A\B"

D::foo();   // using import rules, calls method "foo" of class "D" defined in namespace "B"
            // if class "B\D" not found, it tries to autoload class "B\D"

\B\foo();   // calls function "foo" from namespace "B"

\B::foo();  // calls method "foo" of class "B" from global scope
            // if class "B" not found, it tries to autoload class "B"

// static methods/namespace functions of current namespace

A\B::foo();   // calls method "foo" of class "B" from namespace "A\A"
              // if class "A\A\B" not found, it tries to autoload class "A\A\B"

\A\B::foo();  // calls method "foo" of class "B" from namespace "A"
              // if class "A\B" not found, it tries to autoload class "A\B"
?>

=====================================================================

FAQ: things you need to know about namespaces

This FAQ is split into two sections: common questions, and some specifics of implementation that are helpful to understand fully.

First, the common questions.

   1. If I don't use namespaces, should I care about any of this?
   2. How do I use internal or global classes in a namespace?
   3. How do I use namespaces classes functions, or constants in their own namespace?
   4. How does a name like \my\name or \name resolve?
   5. How does a name like my\name resolve?
   6. How does an unqualified class name like name resolve?
   7. How does an unqualified function name or unqualified constant name like name resolve?

There are a few implementation details of the namespace implementations that are helpful to understand.

   1. Import names cannot conflict with classes defined in the same file.
   2. Nested namespaces are not allowed.
   3. Neither functions nor constants can be imported via the use statement.
   4. Dynamic namespace names (quoted identifiers) should escape backslash.
   5. Undefined Constants referenced using any backslash die with fatal error
   6. Cannot override special constants NULL, TRUE, FALSE, ZEND_THREAD_SAFE or ZEND_DEBUG_BUILD

If I don't use namespaces, should I care about any of this?

No. Namespaces do not affect any existing code in any way, or any as-yet-to-be-written code that does not contain namespaces. You can write this code if you wish:

Example #1 Accessing global classes outside a namespace
<?php
$a = new \stdClass;
?>

This is functionally equivalent to:

Example #2 Accessing global classes outside a namespace
<?php
$a = new stdClass;
?>
How do I use internal or global classes in a namespace?

Example #3 Accessing internal classes in namespaces
<?php
namespace foo;
$a = new \stdClass;

function test(\ArrayObject $typehintexample = null) {}

$a = \DirectoryIterator::CURRENT_AS_FILEINFO;

// extending an internal or global class
class MyException extends \Exception {}
?>
How do I use namespaces classes, functions, or constants in their own namespace?

Example #4 Accessing internal classes, functions or constants in namespaces
<?php
namespace foo;

class MyClass {}

// using a class from the current namespace as a type hint
function test(MyClass $typehintexample = null) {}
// another way to use a class from the current namespace as a type hint
function test(\foo\MyClass $typehintexample = null) {}

// extending a class from the current namespace
class Extended extends MyClass {}

// accessing a global function
$a = \globalfunc();

// accessing a global constant
$b = \INI_ALL;
?>
How does a name like \my\name or \name resolve?

Names that begin with a \ always resolve to what they look like, so \my\name is in fact my\name, and \Exception is Exception.

Example #5 Fully Qualified names
<?php
namespace foo;
$a = new \my\name(); // instantiates "my\name" class
echo \strlen('hi'); // calls function "strlen"
$a = \INI_ALL; // $a is set to the value of constant "INI_ALL"
?>
How does a name like my\name resolve?

Names that contain a backslash but do not begin with a backslash like my\name can be resolved in 2 different ways.

If there is an import statement that aliases another name to my, then the import alias is applied to the my in my\name.

Otherwise, the current namespace name is prepended to my\name.

Example #6 Qualified names
<?php
namespace foo;
use blah\blah as foo;

$a = new my\name(); // instantiates "foo\my\name" class
foo\bar::name(); // calls static method "name" in class "blah\blah\bar"
my\bar(); // calls function "foo\my\bar"
$a = my\BAR; // sets $a to the value of constant "foo\my\BAR"
?>
How does an unqualified class name like name resolve?

Class names that do not contain a backslash like name can be resolved in 2 different ways.

If there is an import statement that aliases another name to name, then the import alias is applied.

Otherwise, the current namespace name is prepended to name.

Example #7 Unqualified class names
<?php
namespace foo;
use blah\blah as foo;

$a = new name(); // instantiates "foo\name" class
foo::name(); // calls static method "name" in class "blah\blah"
?>
How does an unqualified function name or unqualified constant name like name resolve?

Function or constant names that do not contain a backslash like name can be resolved in 2 different ways.

First, the current namespace name is prepended to name.

Finally, if the constant or function name does not exist in the current namespace, a global constant or function name is used if it exists.

Example #8 Unqualified function or constant names
<?php
namespace foo;
use blah\blah as foo;

const FOO = 1;

function my() {}
function foo() {}
function sort(&$a)
{
    sort($a);
    $a = array_flip($a);
    return $a;
}

my(); // calls "foo\my"
$a = strlen('hi'); // calls global function "strlen" because "foo\strlen" does not exist
$arr = array(1,3,2);
$b = sort($arr); // calls function "foo\sort"
$c = foo(); // calls function "foo\foo" - import is not applied

$a = FOO; // sets $a to value of constant "foo\FOO" - import is not applied
$b = INI_ALL; // sets $b to value of global constant "INI_ALL"
?>
Import names cannot conflict with classes defined in the same file.

The following script combinations are legal:

file1.php
<?php
namespace my\stuff;
class MyClass {}
?>

another.php
<?php
namespace another;
class thing {}
?>

file2.php
<?php
namespace my\stuff;
include 'file1.php';
include 'another.php';

use another\thing as MyClass;
$a = new MyClass; // instantiates class "thing" from namespace another
?>

There is no name conflict, even though the class MyClass exists within the my\stuff namespace, because the MyClass definition is in a separate file. However, the next example causes a fatal error on name conflict because MyClass is defined in the same file as the use statement.
<?php
namespace my\stuff;
use another\thing as MyClass;
class MyClass {} // fatal error: MyClass conflicts with import statement
$a = new MyClass;
?>
Nested namespaces are not allowed.

PHP does not allow nesting namespaces
<?php
namespace my\stuff {
    namespace nested {
        class foo {}
    }
}
?>
However, it is easy to simulate nested namespaces like so:
<?php
namespace my\stuff\nested {
    class foo {}
}
?>
Neither functions nor constants can be imported via the use statement.

The only elements that are affected by use statements are namespaces and class names. In order to shorten a long constant or function, import its containing namespace
<?php
namespace mine;
use ultra\long\ns\name;

$a = name\CONSTANT;
name\func();
?>
Dynamic namespace names (quoted identifiers) should escape backslash

It is very important to realize that because the backslash is used as an escape character within strings, it should always be doubled when used inside a string. Otherwise there is a risk of unintended consequences:

Example #9 Dangers of using namespaced names inside a double-quoted string
<?php
$a = new "dangerous\name"; // \n is a newline inside double quoted strings!
$obj = new $a;

$a = new 'not\at\all\dangerous'; // no problems here.
$obj = new $a;
?>
Inside a single-quoted string, the backslash escape sequence is much safer to use, but it is still recommended practice to escape backslashes in all strings as a best practice.
Undefined Constants referenced using any backslash die with fatal error

Any undefined constant that is unqualified like FOO will produce a notice explaining that PHP assumed FOO was the value of the constant. Any constant, qualified or fully qualified, that contains a backslash will produce a fatal error if not found.

Example #10 Undefined constants
<?php
namespace bar;
$a = FOO; // produces notice - undefined constants "FOO" assumed "FOO";
$a = \FOO; // fatal error, undefined namespace constant FOO
$a = Bar\FOO; // fatal error, undefined namespace constant bar\Bar\FOO
$a = \Bar\FOO; // fatal error, undefined namespace constant Bar\FOO
?>
Cannot override special constants NULL, TRUE, FALSE, ZEND_THREAD_SAFE or ZEND_DEBUG_BUILD

Any attempt to define a namespaced constant that is a special, built-in constant results in a fatal error

Example #11 Undefined constants
<?php
namespace bar;
const NULL = 0; // fatal error;
const true = 'stupid'; // also fatal error;
// etc.
?>

=====================================================================
=====================================================================
    * Exceptions
=====================================================================


Exceptions
Table of Contents

    * Extending Exceptions

PHP 5 has an exception model similar to that of other programming languages. An exception can be thrown, and caught ("catched") within PHP. Code may be surrounded in a try block, to facilitate the catching of potential exceptions. Each try must have at least one corresponding catch block. Multiple catch blocks can be used to catch different classes of exeptions. Normal execution (when no exception is thrown within the try block, or when a catch matching the thrown exception's class is not present) will continue after that last catch block defined in sequence. Exceptions can be thrown (or re-thrown) within a catch block.

When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception ..." message, unless a handler has been defined with set_exception_handler().

The thrown object must be an instance of the Exception class or a subclass of Exception. Trying to throw an object that is not will result in a PHP Fatal Error.

    Note:

    Internal PHP functions mainly use Error reporting, only modern Object oriented extensions use exceptions. However, errors can be simply translated to exceptions with ErrorException.

Tip

The Standard PHP Library (SPL) provides a good number of built-in exceptions.

Example #1 Throwing an Exception
<?php
function inverse($x) {
    if (!$x) {
        throw new Exception('Division by zero.');
    }
    else return 1/$x;
}

try {
    echo inverse(5) . "\n";
    echo inverse(0) . "\n";
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "\n";
}

// Continue execution
echo 'Hello World';
?>

The above example will output:

0.2
Caught exception: Division by zero.
Hello World

Example #2 Nested Exception
<?php

class MyException extends Exception { }

class Test {
    public function testing() {
        try {
            try {
                throw new MyException('foo!');
            } catch (MyException $e) {
                /* rethrow it */
                throw $e;
            }
        } catch (Exception $e) {
            var_dump($e->getMessage());
        }
    }
}

$foo = new Test;
$foo->testing();

?>

The above example will output:

string(4) "foo!"

=====================================================================


Extending Exceptions

A User defined Exception class can be defined by extending the built-in Exception class. The members and properties below, show what is accessible within the child class that derives from the built-in Exception class.

Example #1 The Built in Exception class
<?php
class Exception
{
    protected $message = 'Unknown exception';   // exception message
    private   $string;                          // __toString cache
    protected $code = 0;                        // user defined exception code
    protected $file;                            // source filename of exception
    protected $line;                            // source line of exception
    private   $trace;                           // backtrace
    private   $previous;                        // previous exception if nested exception

    public function __construct($message = null, $code = 0, Exception $previous = null);

    final private function __clone();           // Inhibits cloning of exceptions.

    final public  function getMessage();        // message of exception
    final public  function getCode();           // code of exception
    final public  function getFile();           // source filename
    final public  function getLine();           // source line
    final public  function getTrace();          // an array of the backtrace()
    final public  function getPrevious();       // previous exception
    final public  function getTraceAsString();  // formatted string of trace

    /* Overrideable */
    public function __toString();               // formatted string for display
}
?>

If a class extends the built-in Exception class and re-defines the constructor, it is highly recommended that it also call parent::__construct() to ensure all available data has been properly assigned. The __toString() method can be overridden to provide a custom output when the object is presented as a string.

    Note:

    Exceptions cannot be cloned. Attempting to clone an Exception will result in a fatal E_ERROR error.

Example #2 Extending the Exception class (PHP 5.3.0+)
<?php
/**
 * Define a custom exception class
 */
class MyException extends Exception
{
    // Redefine the exception so message isn't optional
    public function __construct($message, $code = 0, Exception $previous = null) {
        // some code
    
        // make sure everything is assigned properly
        parent::__construct($message, $code, $previous);
    }

    // custom string representation of object
    public function __toString() {
        return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
    }

    public function customFunction() {
        echo "A custom function for this type of exception\n";
    }
}


/**
 * Create a class to test the exception
 */
class TestException
{
    public $var;

    const THROW_NONE    = 0;
    const THROW_CUSTOM  = 1;
    const THROW_DEFAULT = 2;

    function __construct($avalue = self::THROW_NONE) {

        switch ($avalue) {
            case self::THROW_CUSTOM:
                // throw custom exception
                throw new MyException('1 is an invalid parameter', 5);
                break;

            case self::THROW_DEFAULT:
                // throw default one.
                throw new Exception('2 is not allowed as a parameter', 6);
                break;

            default: 
                // No exception, object will be created.
                $this->var = $avalue;
                break;
        }
    }
}


// Example 1
try {
    $o = new TestException(TestException::THROW_CUSTOM);
} catch (MyException $e) {      // Will be caught
    echo "Caught my exception\n", $e;
    $e->customFunction();
} catch (Exception $e) {        // Skipped
    echo "Caught Default Exception\n", $e;
}

// Continue execution
var_dump($o); // Null
echo "\n\n";


// Example 2
try {
    $o = new TestException(TestException::THROW_DEFAULT);
} catch (MyException $e) {      // Doesn't match this type
    echo "Caught my exception\n", $e;
    $e->customFunction();
} catch (Exception $e) {        // Will be caught
    echo "Caught Default Exception\n", $e;
}

// Continue execution
var_dump($o); // Null
echo "\n\n";


// Example 3
try {
    $o = new TestException(TestException::THROW_CUSTOM);
} catch (Exception $e) {        // Will be caught
    echo "Default Exception caught\n", $e;
}

// Continue execution
var_dump($o); // Null
echo "\n\n";


// Example 4
try {
    $o = new TestException();
} catch (Exception $e) {        // Skipped, no exception
    echo "Default Exception caught\n", $e;
}

// Continue execution
var_dump($o); // TestException
echo "\n\n";
?>

    Note:

    Versions of PHP 5, prior to PHP 5.3.0 do not support nesting of exceptions. The following code fragment can be used as a replacement MyException class if you wish to run this example.
    <?php
    /**
     * Define a custom exception class
     */
    class MyException extends Exception
    {
        // Redefine the exception so message isn't optional
        public function __construct($message, $code = 0) {
            // some code
        
            // make sure everything is assigned properly
            parent::__construct($message, $code);
        }

        // custom string representation of object
        public function __toString() {
            return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
        }

        public function customFunction() {
            echo "A custom function for this type of exception\n";
        }
    }
    ?>

=====================================================================
=====================================================================
    * References Explained
=====================================================================

Table of Contents

    * What References Are
    * What References Do
    * What References Are Not
    * Passing by Reference
    * Returning References
    * Unsetting References
    * Spotting References

=====================================================================

What References Are

References in PHP are a means to access the same variable content by different names. They are not like C pointers; for instance, you cannot perform pointer arithmetic using them, they are not actual memory addresses, and so on. See What References Are Not for more information. Instead, they are symbol table aliases. Note that in PHP, variable name and variable content are different, so the same content can have different names. The closest analogy is with Unix filenames and files - variable names are directory entries, while variable content is the file itself. References can be likened to hardlinking in Unix filesystem.

=====================================================================


What References Do

There are three basic operations performed using references: assigning by reference, passing by reference, and returning by reference. This section will give an introduction to these operations, with links to further reading.
Assign By Reference

In the first of these, PHP references allow you to make two variables refer to the same content. Meaning, when you do:
<?php
$a =& $b;
?>
it means that $a and $b point to the same content.

    Note:

    $a and $b are completely equal here. $a is not pointing to $b or vice versa. $a and $b are pointing to the same place.

    Note:

    If you assign, pass, or return an undefined variable by reference, it will get created.

    Example #1 Using references with undefined variables
    <?php
    function foo(&$var) { }

    foo($a); // $a is "created" and assigned to null

    $b = array();
    foo($b['b']);
    var_dump(array_key_exists('b', $b)); // bool(true)

    $c = new StdClass;
    foo($c->d);
    var_dump(property_exists($c, 'd')); // bool(true)
    ?>

The same syntax can be used with functions that return references, and with the new operator (since PHP 4.0.4 and before PHP 5.0.0):
<?php
$foo =& find_var($bar);
?>
Since PHP 5, new returns a reference automatically, so using =& in this context is deprecated and produces an E_DEPRECATED message in PHP 5.3 and later, and an E_STRICT message in earlier versions. (Technically, the difference is that, in PHP 5, object variables, much like resources, are a mere pointer to the actual object data, so these object references are not "references" in the same sense used before (aliases). For more information, see Objects and references.)
Warning

If you assign a reference to a variable declared global inside a function, the reference will be visible only inside the function. You can avoid this by using the $GLOBALS array.

Example #2 Referencing global variables inside functions
<?php
$var1 = "Example variable";
$var2 = "";

function global_references($use_globals)
{
    global $var1, $var2;
    if (!$use_globals) {
        $var2 =& $var1; // visible only inside the function
    } else {
        $GLOBALS["var2"] =& $var1; // visible also in global context
    }
}

global_references(false);
echo "var2 is set to '$var2'\n"; // var2 is set to ''
global_references(true);
echo "var2 is set to '$var2'\n"; // var2 is set to 'Example variable'
?>
Think about global $var; as a shortcut to $var =& $GLOBALS['var'];. Thus assigning another reference to $var only changes the local variable's reference.

    Note:

    If you assign a value to a variable with references in a foreach statement, the references are modified too.

    Example #3 References and foreach statement
    <?php
    $ref = 0;
    $row =& $ref;
    foreach (array(1, 2, 3) as $row) {
        // do something
    }
    echo $ref; // 3 - last element of the iterated array
    ?>

While not being strictly an assignment by reference, expressions created with the language construct array() can also behave as such by prefixing & to the array element to add. Example:
<?php
$a = 1;
$b = array(2, 3);
$arr = array(&$a, &$b[0], &$b[1]);
$arr[0]++; $arr[1]++; $arr[2]++;
/* $a == 2, $b == array(3, 4); */
?>

Note, however, that references inside arrays are potentially dangerous. Doing a normal (not by reference) assignment with a reference on the right side does not turn the left side into a reference, but references inside arrays are preserved in these normal assignments. This also applies to function calls where the array is passed by value. Example:
<?php
/* Assignment of scalar variables */
$a = 1;
$b =& $a;
$c = $b;
$c = 7; //$c is not a reference; no change to $a or $b

/* Assignment of array variables */
$arr = array(1);
$a =& $arr[0]; //$a and $arr[0] are in the same reference set
$arr2 = $arr; //not an assignment-by-reference!
$arr2[0]++;
/* $a == 2, $arr == array(2) */
/* The contents of $arr are changed even though it's not a reference! */
?>
In other words, the reference behavior of arrays is defined in an element-by-element basis; the reference behavior of individual elements is dissociated from the reference status of the array container.
Pass By Reference

The second thing references do is to pass variables by reference. This is done by making a local variable in a function and a variable in the calling scope referencing the same content. Example:
<?php
function foo(&$var)
{
    $var++;
}

$a=5;
foo($a);
?>
will make $a to be 6. This happens because in the function foo the variable $var refers to the same content as $a. For more information on this, read the passing by reference section.
Return By Reference

The third thing references can do is return by reference.

=====================================================================


What References Are Not

As said before, references are not pointers. That means, the following construct won't do what you expect:
<?php
function foo(&$var)
{
    $var =& $GLOBALS["baz"];
}
foo($bar); 
?>

What happens is that $var in foo will be bound with $bar in the caller, but then re-bound with $GLOBALS["baz"]. There's no way to bind $bar in the calling scope to something else using the reference mechanism, since $bar is not available in the function foo (it is represented by $var, but $var has only variable contents and not name-to-value binding in the calling symbol table). You can use returning references to reference variables selected by the function.

=====================================================================

Passing by Reference

You can pass a variable by reference to a function so the function can modify the variable. The syntax is as follows:
<?php
function foo(&$var)
{
    $var++;
}

$a=5;
foo($a);
// $a is 6 here
?>

    Note: There is no reference sign on a function call - only on function definitions. Function definitions alone are enough to correctly pass the argument by reference. As of PHP 5.3.0, you will get a warning saying that "call-time pass-by-reference" is deprecated when you use & in foo(&$a);. 

The following things can be passed by reference:

    * Variables, i.e. foo($a)
    * New statements, i.e. foo(new foobar())
    *

      References returned from functions, i.e.:
      <?php
      function foo(&$var)
      {
          $var++;
      }
      function &bar()
      {
          $a = 5;
          return $a;
      }
      foo(bar());
      ?>
      See more about returning by reference.

No other expressions should be passed by reference, as the result is undefined. For example, the following examples of passing by reference are invalid:
<?php
function foo(&$var)
{
    $var++;
}
function bar() // Note the missing &
{
    $a = 5;
    return $a;
}
foo(bar()); // Produces fatal error since PHP 5.0.5

foo($a = 5); // Expression, not variable
foo(5); // Produces fatal error
?>
These requirements are for PHP 4.0.4 and later. 

=====================================================================


Returning References

Returning by reference is useful when you want to use a function to find to which variable a reference should be bound. Do not use return-by-reference to increase performance. The engine will automatically optimize this on its own. Only return references when you have a valid technical reason to do so. To return references, use this syntax:
<?php
class foo {
    public $value = 42;

    public function &getValue() {
        return $this->value;
    }
}

$obj = new foo;
$myValue = &$obj->getValue(); // $myValue is a reference to $obj->value, which is 42.
$obj->value = 2;
echo $myValue;                // prints the new value of $obj->value, i.e. 2.
?>
In this example, the property of the object returned by the getValue function would be set, not the copy, as it would be without using reference syntax.

    Note: Unlike parameter passing, here you have to use & in both places - to indicate that you want to return by reference, not a copy, and to indicate that reference binding, rather than usual assignment, should be done for $myValue. 

    Note: If you try to return a reference from a function with the syntax: return ($this->value); this will not work as you are attempting to return the result of an expression, and not a variable, by reference. You can only return variables by reference from a function - nothing else. Since PHP 4.4.0 in the PHP4 branch, and PHP 5.1.0 in the PHP5 branch, an E_NOTICE error is issued if the code tries to return a dynamic expression or a result of the new operator. 

To use the returned reference, you must use reference assigment:
<?php
function &collector() {
  static $collection = array();
  return $collection;
}
$collection = &collector();
$collection[] = 'foo';
?>
To pass the returned reference to another function expecting a reference you can use this syntax:
<?php
function &collector() {
  static $collection = array();
  return $collection;
}
array_push(collector(), 'foo');
?>

    Note: Note that array_push(&collector(), 'foo'); will not work, it results in a fatal error. 

=====================================================================


Unsetting References

When you unset the reference, you just break the binding between variable name and variable content. This does not mean that variable content will be destroyed. For example:
<?php
$a = 1;
$b =& $a;
unset($a); 
?>
won't unset $b, just $a.

Again, it might be useful to think about this as analogous to the Unix unlink call.

=====================================================================


Spotting References

Many syntax constructs in PHP are implemented via referencing mechanisms, so everything mentioned herein about reference binding also applies to these constructs. Some constructs, like passing and returning by reference, are mentioned above. Other constructs that use references are:
global References

When you declare a variable as global $var you are in fact creating reference to a global variable. That means, this is the same as:
<?php
$var =& $GLOBALS["var"];
?>

This also means that unsetting $var won't unset the global variable.
$this

In an object method, $this is always a reference to the caller object.

=====================================================================
=====================================================================
    * Predefined Variables
=====================================================================

PHP provides a large number of predefined variables to all scripts. The variables represent everything from external variables to built-in environment variables, last error messages to last retrieved headers.

See also the FAQ titled "How does register_globals affect me?"
Table of Contents

    * Superglobals — Superglobals are built-in variables that are always available in all scopes
    * $GLOBALS — References all variables available in global scope
    * $_SERVER — Server and execution environment information
    * $_GET — HTTP GET variables
    * $_POST — HTTP POST variables
    * $_FILES — HTTP File Upload variables
    * $_REQUEST — HTTP Request variables
    * $_SESSION — Session variables
    * $_ENV — Environment variables
    * $_COOKIE — HTTP Cookies
    * $php_errormsg — The previous error message
    * $HTTP_RAW_POST_DATA — Raw POST data
    * $http_response_header — HTTP response headers
    * $argc — The number of arguments passed to script
    * $argv — Array of arguments passed to script

=====================================================================


Superglobals

Superglobals — Superglobals are built-in variables that are always available in all scopes
Description

Several predefined variables in PHP are "superglobals", which means they are available in all scopes throughout a script. There is no need to do global $variable; to access them within functions or methods.

These superglobal variables are:

    * $GLOBALS
    * $_SERVER
    * $_GET
    * $_POST
    * $_FILES
    * $_COOKIE
    * $_SESSION
    * $_REQUEST
    * $_ENV

Changelog

Version 	Description
4.1.0 	Superglobals were introduced to PHP.
Notes

    Note: Variable availability

    By default, all of the superglobals are available but there are directives that affect this availability. For further information, refer to the documentation for variables_order.

    Note: Dealing with register_globals

    If the deprecated register_globals directive is set to on then the variables within will also be made available in the global scope of the script. For example, $_POST['foo'] would also exist as $foo.

    For related information, see the FAQ titled "How does register_globals affect me?"

    Note: Variable variables

    Superglobals cannot be used as variable variables inside functions or class methods.

See Also
    * variable scope
    * The variables_order directive
    * The filter extension

=====================================================================


$GLOBALS

(PHP 4, PHP 5)

$GLOBALS — References all variables available in global scope
Description

An associative array containing references to all variables which are currently defined in the global scope of the script. The variable names are the keys of the array.
Examples

Example #1 $GLOBALS example
<?php
function test() {
    $foo = "local variable";

    echo '$foo in global scope: ' . $GLOBALS["foo"] . "\n";
    echo '$foo in current scope: ' . $foo . "\n";
}

$foo = "Example content";
test();
?>

The above example will output something similar to:

$foo in global scope: Example content
$foo in current scope: local variable

Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

    Note: Variable availability

    Unlike all of the other superglobals, $GLOBALS has essentially always been available in PHP.

=====================================================================


$_SERVER
$HTTP_SERVER_VARS [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_SERVER -- $HTTP_SERVER_VARS [deprecated] — Server and execution environment information
Description

$_SERVER is an array containing information such as headers, paths, and script locations. The entries in this array are created by the web server. There is no guarantee that every web server will provide any of these; servers may omit some, or provide others not listed here. That said, a large number of these variables are accounted for in the » CGI/1.1 specification, so you should be able to expect those.

$HTTP_SERVER_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_SERVER_VARS and $_SERVER are different variables and that PHP handles them as such)
Indices

You may or may not find any of the following elements in $_SERVER. Note that few, if any, of these will be available (or indeed have any meaning) if running PHP on the command line.

'PHP_SELF'
    The filename of the currently executing script, relative to the document root. For instance, $_SERVER['PHP_SELF'] in a script at the address http://example.com/test.php/foo.bar would be /test.php/foo.bar. The __FILE__ constant contains the full path and filename of the current (i.e. included) file. If PHP is running as a command-line processor this variable contains the script name since PHP 4.3.0. Previously it was not available. 
'argv'
    Array of arguments passed to the script. When the script is run on the command line, this gives C-style access to the command line parameters. When called via the GET method, this will contain the query string. 
'argc'
    Contains the number of command line parameters passed to the script (if run on the command line). 
'GATEWAY_INTERFACE'
    What revision of the CGI specification the server is using; i.e. 'CGI/1.1'. 
'SERVER_ADDR'
    The IP address of the server under which the current script is executing. 
'SERVER_NAME'
    The name of the server host under which the current script is executing. If the script is running on a virtual host, this will be the value defined for that virtual host. 
'SERVER_SOFTWARE'
    Server identification string, given in the headers when responding to requests. 
'SERVER_PROTOCOL'
    Name and revision of the information protocol via which the page was requested; i.e. 'HTTP/1.0'; 
'REQUEST_METHOD'
    Which request method was used to access the page; i.e. 'GET', 'HEAD', 'POST', 'PUT'.

        Note:

        PHP script is terminated after sending headers (it means after producing any output without output buffering) if the request method was HEAD.

'REQUEST_TIME'
    The timestamp of the start of the request. Available since PHP 5.1.0. It is float with microseconds since PHP 5.4.0. 
'QUERY_STRING'
    The query string, if any, via which the page was accessed. 
'DOCUMENT_ROOT'
    The document root directory under which the current script is executing, as defined in the server's configuration file. 
'HTTP_ACCEPT'
    Contents of the Accept: header from the current request, if there is one. 
'HTTP_ACCEPT_CHARSET'
    Contents of the Accept-Charset: header from the current request, if there is one. Example: 'iso-8859-1,*,utf-8'. 
'HTTP_ACCEPT_ENCODING'
    Contents of the Accept-Encoding: header from the current request, if there is one. Example: 'gzip'. 
'HTTP_ACCEPT_LANGUAGE'
    Contents of the Accept-Language: header from the current request, if there is one. Example: 'en'. 
'HTTP_CONNECTION'
    Contents of the Connection: header from the current request, if there is one. Example: 'Keep-Alive'. 
'HTTP_HOST'
    Contents of the Host: header from the current request, if there is one. 
'HTTP_REFERER'
    The address of the page (if any) which referred the user agent to the current page. This is set by the user agent. Not all user agents will set this, and some provide the ability to modify HTTP_REFERER as a feature. In short, it cannot really be trusted. 
'HTTP_USER_AGENT'
    Contents of the User-Agent: header from the current request, if there is one. This is a string denoting the user agent being which is accessing the page. A typical example is: Mozilla/4.5 [en] (X11; U; Linux 2.2.9 i586). Among other things, you can use this value with get_browser() to tailor your page's output to the capabilities of the user agent. 
'HTTPS'
    Set to a non-empty value if the script was queried through the HTTPS protocol.

        Note: Note that when using ISAPI with IIS, the value will be off if the request was not made through the HTTPS protocol. 

'REMOTE_ADDR'
    The IP address from which the user is viewing the current page. 
'REMOTE_HOST'
    The Host name from which the user is viewing the current page. The reverse dns lookup is based off the REMOTE_ADDR of the user.

        Note: Your web server must be configured to create this variable. For example in Apache you'll need HostnameLookups On inside httpd.conf for it to exist. See also gethostbyaddr(). 

'REMOTE_PORT'
    The port being used on the user's machine to communicate with the web server. 
'SCRIPT_FILENAME'

    The absolute pathname of the currently executing script.

        Note:

        If a script is executed with the CLI, as a relative path, such as file.php or ../file.php, $_SERVER['SCRIPT_FILENAME'] will contain the relative path specified by the user.

'SERVER_ADMIN'
    The value given to the SERVER_ADMIN (for Apache) directive in the web server configuration file. If the script is running on a virtual host, this will be the value defined for that virtual host. 
'SERVER_PORT'
    The port on the server machine being used by the web server for communication. For default setups, this will be '80'; using SSL, for instance, will change this to whatever your defined secure HTTP port is. 
'SERVER_SIGNATURE'
    String containing the server version and virtual host name which are added to server-generated pages, if enabled. 
'PATH_TRANSLATED'
    Filesystem- (not document root-) based path to the current script, after the server has done any virtual-to-real mapping.

        Note: As of PHP 4.3.2, PATH_TRANSLATED is no longer set implicitly under the Apache 2 SAPI in contrast to the situation in Apache 1, where it's set to the same value as the SCRIPT_FILENAME server variable when it's not populated by Apache. This change was made to comply with the CGI specification that PATH_TRANSLATED should only exist if PATH_INFO is defined. Apache 2 users may use AcceptPathInfo = On inside httpd.conf to define PATH_INFO. 

'SCRIPT_NAME'
    Contains the current script's path. This is useful for pages which need to point to themselves. The __FILE__ constant contains the full path and filename of the current (i.e. included) file. 
'REQUEST_URI'
    The URI which was given in order to access this page; for instance, '/index.html'. 
'PHP_AUTH_DIGEST'
    When doing Digest HTTP authentication this variable is set to the 'Authorization' header sent by the client (which you should then use to make the appropriate validation). 
'PHP_AUTH_USER'
    When doing HTTP authentication this variable is set to the username provided by the user. 
'PHP_AUTH_PW'
    When doing HTTP authentication this variable is set to the password provided by the user. 
'AUTH_TYPE'
    When doing HTTP authenticated this variable is set to the authentication type. 
'PATH_INFO'
    Contains any client-provided pathname information trailing the actual script filename but preceding the query string, if available. For instance, if the current script was accessed via the URL http://www.example.com/php/path_info.php/some/stuff?foo=bar, then $_SERVER['PATH_INFO'] would contain /some/stuff. 
'ORIG_PATH_INFO'
    Original version of 'PATH_INFO' before processed by PHP. 

Changelog

Version 	Description
4.1.0 	Introduced $_SERVER that deprecated $HTTP_SERVER_VARS.
Examples

Example #1 $_SERVER example
<?php
echo $_SERVER['SERVER_NAME'];
?>

The above example will output something similar to:

www.example.com

Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

See Also

    * The filter extension


=====================================================================


$_GET
$HTTP_GET_VARS [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_GET -- $HTTP_GET_VARS [deprecated] — HTTP GET variables
Description

An associative array of variables passed to the current script via the URL parameters.

$HTTP_GET_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_GET_VARS and $_GET are different variables and that PHP handles them as such)
Changelog

Version 	Description
4.1.0 	Introduced $_GET that deprecated $HTTP_GET_VARS.
Examples

Example #1 $_GET example
<?php
echo 'Hello ' . htmlspecialchars($_GET["name"]) . '!';
?>

Assuming the user entered http://example.com/?name=Hannes

The above example will output something similar to:

Hello Hannes!

Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

    Note:

    The GET variables are passed through urldecode().

See Also

    * Handling external variables
    * The filter extension

=====================================================================


$_POST
$HTTP_POST_VARS [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_POST -- $HTTP_POST_VARS [deprecated] — HTTP POST variables
Description

An associative array of variables passed to the current script via the HTTP POST method.

$HTTP_POST_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_POST_VARS and $_POST are different variables and that PHP handles them as such)
Changelog

Version 	Description
4.1.0 	Introduced $_POST that deprecated $HTTP_POST_VARS.
Examples

Example #1 $_POST example
<?php
echo 'Hello ' . htmlspecialchars($_POST["name"]) . '!';
?>

Assuming the user POSTed name=Hannes

The above example will output something similar to:

Hello Hannes!

Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

See Also

    * Handling external variables
    * The filter extension

=====================================================================


$_FILES
$HTTP_POST_FILES [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_FILES -- $HTTP_POST_FILES [deprecated] — HTTP File Upload variables
Description

An associative array of items uploaded to the current script via the HTTP POST method.

$HTTP_POST_FILES contains the same initial information, but is not a superglobal. (Note that $HTTP_POST_FILES and $_FILES are different variables and that PHP handles them as such)
Changelog

Version 	Description
4.1.0 	Introduced $_FILES that deprecated $HTTP_POST_FILES.
Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

See Also

    * move_uploaded_file() - Moves an uploaded file to a new location
    * Handling File Uploads

=====================================================================


$_REQUEST

(PHP 4 >= 4.1.0, PHP 5)

$_REQUEST — HTTP Request variables
Description

An associative array that by default contains the contents of $_GET, $_POST and $_COOKIE.
Changelog

Version 	Description
5.3.0 	Introduced request_order. This directive affects the contents of $_REQUEST.
4.3.0 	$_FILES information was removed from $_REQUEST.
4.1.0 	Introduced $_REQUEST.
Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

    Note:

    When running on the command line , this will not include the argv and argc entries; these are present in the $_SERVER array.

    Note:

    The variables in $_REQUEST are provided to the script via the GET, POST, and COOKIE input mechanisms and therefore could be modified by the remote user and cannot be trusted. The presence and order of variables listed in this array is defined according to the PHP variables_order configuration directive.

See Also

    * import_request_variables() - Import GET/POST/Cookie variables into the global scope
    * Handling external variables
    * The filter extension

=====================================================================


$_SESSION
$HTTP_SESSION_VARS [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_SESSION -- $HTTP_SESSION_VARS [deprecated] — Session variables
Description

An associative array containing session variables available to the current script. See the Session functions documentation for more information on how this is used.

$HTTP_SESSION_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_SESSION_VARS and $_SESSION are different variables and that PHP handles them as such)
Changelog

Version 	Description
4.1.0 	Introduced $_SESSION that deprecated $HTTP_SESSION_VARS.
Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

See Also

    * session_start() - Initialize session data

=====================================================================


$_ENV
$HTTP_ENV_VARS [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_ENV -- $HTTP_ENV_VARS [deprecated] — Environment variables
Description

An associative array of variables passed to the current script via the environment method.

These variables are imported into PHP's global namespace from the environment under which the PHP parser is running. Many are provided by the shell under which PHP is running and different systems are likely running different kinds of shells, a definitive list is impossible. Please see your shell's documentation for a list of defined environment variables.

Other environment variables include the CGI variables, placed there regardless of whether PHP is running as a server module or CGI processor.

$HTTP_ENV_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_ENV_VARS and $_ENV are different variables and that PHP handles them as such)
Changelog

Version 	Description
4.1.0 	Introduced $_ENV that deprecated $HTTP_ENV_VARS.
Examples

Example #1 $_ENV example
<?php
echo 'My username is ' .$_ENV["USER"] . '!';
?>

Assuming "bjori" executes this script

The above example will output something similar to:

My username is bjori!

Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

See Also

    * getenv() - Gets the value of an environment variable
    * The filter extension

=====================================================================


$_COOKIE
$HTTP_COOKIE_VARS [deprecated]

(PHP 4 >= 4.1.0, PHP 5)

$_COOKIE -- $HTTP_COOKIE_VARS [deprecated] — HTTP Cookies
Description

An associative array of variables passed to the current script via HTTP Cookies.

$HTTP_COOKIE_VARS contains the same initial information, but is not a superglobal. (Note that $HTTP_COOKIE_VARS and $_COOKIE are different variables and that PHP handles them as such)
Changelog

Version 	Description
4.1.0 	Introduced $_COOKIE that deprecated $HTTP_COOKIE_VARS.
Examples

Example #1 $_COOKIE example
<?php
echo 'Hello ' . htmlspecialchars($_COOKIE["name"]) . '!';
?>

Assuming the "name" cookie has been set earlier

The above example will output something similar to:

Hello Hannes!

Notes

    Note:

    This is a 'superglobal', or automatic global, variable. This simply means that it is available in all scopes throughout a script. There is no need to do global $variable; to access it within functions or methods. 

See Also

    * setcookie() - Send a cookie
    * Handling external variables
    * The filter extension

=====================================================================


$php_errormsg

(PHP 4, PHP 5)

$php_errormsg — The previous error message
Description

$php_errormsg is a variable containing the text of the last error message generated by PHP. This variable will only be available within the scope in which the error occurred, and only if the track_errors configuration option is turned on (it defaults to off).

    Note: This variable is only available when track_errors is enabled in php.ini. 

Warning

If a user defined error handler (set_error_handler()) is set $php_errormsg is only set if the error handler returns FALSE
Examples

Example #1 $php_errormsg example
<?php
@strpos();
echo $php_errormsg;
?>

The above example will output something similar to:

Wrong parameter count for strpos()

=====================================================================


$HTTP_RAW_POST_DATA

(PHP 4, PHP 5)

$HTTP_RAW_POST_DATA — Raw POST data
Description

$HTTP_RAW_POST_DATA contains the raw POST data. See always_populate_raw_post_data

=====================================================================


$http_response_header

(PHP 4 >= 4.0.4, PHP 5)

$http_response_header — HTTP response headers
Description

The $http_response_header array is similar to the get_headers() function. When using the HTTP wrapper, $http_response_header will be populated with the HTTP response headers. $http_response_header will be created in the local scope.
Examples

Example #1 $http_response_header example
<?php
function get_contents() {
  file_get_contents("http://example.com");
  var_dump($http_response_header);
}
get_contents();
var_dump($http_response_header);
?>

The above example will output something similar to:

array(9) {
  [0]=>
  string(15) "HTTP/1.1 200 OK"
  [1]=>
  string(35) "Date: Sat, 12 Apr 2008 17:30:38 GMT"
  [2]=>
  string(29) "Server: Apache/2.2.3 (CentOS)"
  [3]=>
  string(44) "Last-Modified: Tue, 15 Nov 2005 13:24:10 GMT"
  [4]=>
  string(27) "ETag: "280100-1b6-80bfd280""
  [5]=>
  string(20) "Accept-Ranges: bytes"
  [6]=>
  string(19) "Content-Length: 438"
  [7]=>
  string(17) "Connection: close"
  [8]=>
  string(38) "Content-Type: text/html; charset=UTF-8"
}
NULL

=====================================================================


$argc

(PHP 4, PHP 5)

$argc — The number of arguments passed to script
Description

Contains the number of arguments passed to the current script when running from the command line.

    Note: The script's filename is always passed as an argument to the script, therefore the minimum value of $argc is 1. 

    Note: This variable is not available when register_argc_argv is disabled. 

Examples

Example #1 $argc example
<?php
var_dump($argc);
?>

When executing the example with: php script.php arg1 arg2 arg3

The above example will output something similar to:

int(4)

=====================================================================


$argv

(PHP 4, PHP 5)

$argv — Array of arguments passed to script
Description

Contains an array of all the arguments passed to the script when running from the command line.

    Note: The first argument $argv[0] is always the name that was used to run the script. 

    Note: This variable is not available when register_argc_argv is disabled. 

Examples

Example #1 $argv example
<?php
var_dump($argv);
?>

When executing the example with: php script.php arg1 arg2 arg3

The above example will output something similar to:

array(4) {
  [0]=>
  string(10) "script.php"
  [1]=>
  string(4) "arg1"
  [2]=>
  string(4) "arg2"
  [3]=>
  string(4) "arg3"
}

See Also

    * getopt() - Gets options from the command line argument list

=====================================================================
=====================================================================
    * Predefined Exceptions
=====================================================================

Table of Contents
    * Exception
    * ErrorException

See also the SPL Exceptions

=====================================================================


Exception
Introduction

Exception is the base class for all Exceptions.
Class synopsis
Exception {
/* Properties */
protected string $Exception->message ;
protected int $code ;
protected string $file ;
protected int $line ;
/* Methods */
public Exception::__construct ([ string $message = "" [, int $code = 0 [, Exception $previous = NULL ]]] )
final public string Exception::getMessage ( void )
final public Exception Exception::getPrevious ( void )
final public mixed Exception::getCode ( void )
final public string Exception::getFile ( void )
final public int Exception::getLine ( void )
final public array Exception::getTrace ( void )
final public string Exception::getTraceAsString ( void )
public string Exception::__toString ( void )
final private void Exception::__clone ( void )
}
Properties

message

    The exception message
code

    The Exception code
file

    The filename where the exception was thrown
line

    The line where the exception was thrown

Table of Contents

    * Exception::__construct — Construct the exception
    * Exception::getMessage — Gets the Exception message
    * Exception::getPrevious — Returns previous Exception
    * Exception::getCode — Gets the Exception code
    * Exception::getFile — Gets the file in which the exception occurred
    * Exception::getLine — Gets the line in which the exception occurred
    * Exception::getTrace — Gets the stack trace
    * Exception::getTraceAsString — Gets the stack trace as a string
    * Exception::__toString — String representation of the exception
    * Exception::__clone — Clone the exception

=====================================================================


Exception::__construct

(PHP 5 >= 5.1.0)

Exception::__construct — Construct the exception
Description
public Exception::__construct() ([ string $message = "" [, int $code = 0 [, Exception $previous = NULL ]]] )

Constructs the Exception.
Parameters

message

    The Exception message to throw.
code

    The Exception code.
previous

    The previous exception used for the exception chaining.

Changelog

Version 	Description
5.3.0 	The previous parameter was added.
Notes

    Note:

    The message is NOT binary safe.

=====================================================================


Exception::getMessage

(PHP 5 >= 5.1.0)

Exception::getMessage — Gets the Exception message
Description
final public string Exception::getMessage ( void )

Returns the Exception message.
Parameters

This function has no parameters.
Return Values

Returns the Exception message as a string.
Examples

Example #1 Exception::getMessage() example
<?php
try {
    throw new Exception("Some error message");
} catch(Exception $e) {
    echo $e->getMessage();
}
?>

The above example will output something similar to:

Some error message

=====================================================================


Exception::getPrevious

(PHP 5 >= 5.3.0)

Exception::getPrevious — Returns previous Exception
Description
final public Exception Exception::getPrevious ( void )

Returns previous Exception (the third parameter of Exception::__construct()).
Parameters

This function has no parameters.
Return Values

Returns the previous Exception if available or NULL otherwise.
Examples

Example #1 Exception::getPrevious() example

Looping over, and printing out, exception trace.
<?php
class MyCustomException extends Exception {}

function doStuff() {
    try {
        throw new InvalidArgumentException("You are doing it wrong!", 112);
    } catch(Exception $e) {
        throw new MyCustomException("Something happend", 911, $e);
    }
}


try {
    doStuff();
} catch(Exception $e) {
    do {
        printf("%s:%d %s (%d) [%s]\n", $e->getFile(), $e->getLine(), $e->getMessage(), $e->getCode(), get_class($e));
    } while($e = $e->getPrevious());
}
?>

The above example will output something similar to:

/home/bjori/ex.php:8 Something happend (911) [MyCustomException]
/home/bjori/ex.php:6 You are doing it wrong! (112) [InvalidArgumentException]

=====================================================================


Exception::getCode

(PHP 5 >= 5.1.0)

Exception::getCode — Gets the Exception code
Description
final public mixed Exception::getCode ( void )

Returns the Exception code.
Parameters

This function has no parameters.
Return Values

Returns the exception code as integer in Exception but possibly as other type in Exception descendants (for example as string in PDOException).
Examples

Example #1 Exception::getCode() example
<?php
try {
    throw new Exception("Some error message", 30);
} catch(Exception $e) {
    echo "The exception code is: " . $e->getCode();
}
?>

The above example will output something similar to:

The exception code is: 30

=====================================================================


Exception::getFile

(PHP 5 >= 5.1.0)

Exception::getFile — Gets the file in which the exception occurred
Description
final public string Exception::getFile ( void )

Get the name of the file the exception was created.
Parameters

This function has no parameters.
Return Values

Returns the filename in which the exception was created.
Examples

Example #1 Exception::getFile() example
<?php
try {
    throw new Exception;
} catch(Exception $e) {
    echo $e->getFile();
}
?>

The above example will output something similar to:

/home/bjori/tmp/ex.php

=====================================================================


Exception::getLine

(PHP 5 >= 5.1.0)

Exception::getLine — Gets the line in which the exception occurred
Description
final public int Exception::getLine ( void )

Get line number where the exception was created.
Parameters

This function has no parameters.
Return Values

Returns the line number where the exception was created.
Examples

Example #1 Exception::getLine() example
<?php
try {
    throw new Exception("Some error message");
} catch(Exception $e) {
    echo "The exception was created on line: " . $e->getLine();
}
?>

The above example will output something similar to:

The exception was created on line: 3

=====================================================================


Exception::getTrace

(PHP 5 >= 5.1.0)

Exception::getTrace — Gets the stack trace
Description
final public array Exception::getTrace ( void )

Returns the Exception stack trace.
Parameters

This function has no parameters.
Return Values

Returns the Exception stack trace as an array.
Examples

Example #1 Exception::getTrace() example
<?php
function test() {
 throw new Exception;
}

try {
 test();
} catch(Exception $e) {
 var_dump($e->getTrace());
}
?>

The above example will output something similar to:

array(1) {
  [0]=>
  array(4) {
    ["file"]=>
    string(22) "/home/bjori/tmp/ex.php"
    ["line"]=>
    int(7)
    ["function"]=>
    string(4) "test"
    ["args"]=>
    array(0) {
    }
  }
}

=====================================================================


Exception::getTraceAsString

(PHP 5 >= 5.1.0)

Exception::getTraceAsString — Gets the stack trace as a string
Description
final public string Exception::getTraceAsString ( void )

Returns the Exception stack trace as a string.
Parameters

This function has no parameters.
Return Values

Returns the Exception stack trace as a string.
Examples

Example #1 Exception::getTraceAsString() example
<?php
function test() {
    throw new Exception;
}

try {
    test();
} catch(Exception $e) {
    echo $e->getTraceAsString();
}
?>

The above example will output something similar to:

#0 /home/bjori/tmp/ex.php(7): test()
#1 {main}

=====================================================================


Exception::__toString

(PHP 5 >= 5.1.0)

Exception::__toString — String representation of the exception
Description
public string Exception::__toString ( void )

Returns the string representation of the exception.
Parameters

This function has no parameters.
Return Values

Returns the string representation of the exception.
Examples

Example #1 Exception::__toString() example
<?php
try {
    throw new Exception("Some error message");
} catch(Exception $e) {
    echo $e;
}
?>

The above example will output something similar to:

exception 'Exception' with message 'Some error message' in /home/bjori/tmp/ex.php:3
Stack trace:
#0 {main}

=====================================================================


Exception::__clone

(PHP 5 >= 5.1.0)

Exception::__clone — Clone the exception
Description
final private void Exception::__clone ( void )

Tries to clone the Exception, which results in Fatal error.
Parameters

This function has no parameters.
Return Values

No value is returned.
Errors/Exceptions

Exceptions are not clonable.

=====================================================================


ErrorException
Introduction

An Error Exception.
Class synopsis
ErrorException extends Exception {
/* Properties */
protected int $ErrorException->severity ;
/* Methods */
public ErrorException::__construct ([ string $message [, int $code [, int $severity [, string $filename [, int $lineno ]]]]] )
final public int ErrorException::getSeverity ( void )
/* Inherited methods */
final public string Exception::getMessage ( void )
final public Exception Exception::getPrevious ( void )
final public mixed Exception::getCode ( void )
final public string Exception::getFile ( void )
final public int Exception::getLine ( void )
final public array Exception::getTrace ( void )
final public string Exception::getTraceAsString ( void )
public string Exception::__toString ( void )
final private void Exception::__clone ( void )
}
Properties

severity

    The severity of the exception

Examples

Example #1 Use set_error_handler() to change error messages into ErrorException.
<?php
function exception_error_handler($errno, $errstr, $errfile, $errline ) {
    throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
}
set_error_handler("exception_error_handler");

/* Trigger exception */
strpos();
?>

The above example will output something similar to:

Fatal error: Uncaught exception 'ErrorException' with message 'Wrong parameter count for strpos()' in /home/bjori/tmp/ex.php:8
Stack trace:
#0 [internal function]: exception_error_handler(2, 'Wrong parameter...', '/home/bjori/php...', 8, Array)
#1 /home/bjori/php/cleandocs/test.php(8): strpos()
#2 {main}
  thrown in /home/bjori/tmp/ex.php on line 8

Table of Contents

    * ErrorException::__construct — Construct the exception
    * ErrorException::getSeverity — Gets the exception severity

=====================================================================


ErrorException::__construct

(PHP 5 >= 5.1.0)

ErrorException::__construct — Construct the exception
Description
public ErrorException::__construct() ([ string $message [, int $code [, int $severity [, string $filename [, int $lineno ]]]]] )

Constructs the Exception.
Parameters

message

    The Exception message to throw.
code

    The Exception code.
severity

    The severity level of the exception.
filename

    The filename where the exception is thrown.
lineno

    The line number where the exception is thrown.

=====================================================================


ErrorException::getSeverity

(PHP 5 >= 5.1.0)

ErrorException::getSeverity — Gets the exception severity
Description
final public int ErrorException::getSeverity ( void )

Returns the severity of the exception.
Parameters

This function has no parameters.
Return Values

Returns the severity level of the exception.
Examples

Example #1 ErrorException::getSeverity() example
<?php
try {
    throw new ErrorException("Exception message", 0, 75);
} catch(ErrorException $e) {
    echo "This exception severity is: " . $e->getSeverity();
}
?>

The above example will output something similar to:

This exception severity is: 75

=====================================================================

Predefined Interfaces
Table of Contents

    * Traversable
    * Iterator
    * IteratorAggregate
    * ArrayAccess
    * Serializable

I'm sorry but I'm not interested in Interfaces right now.
Here's where we are:

http://127.0.0.1/php/php.net-ref/manual/reserved.interfaces.html

And after Interfaces We still have these left to do:

# Context options and parameters

    * Socket context options — Socket context option listing
    * HTTP context options — HTTP context option listing
    * FTP context options — FTP context option listing
    * SSL context options — SSL context option listing
    * CURL context options — CURL context option listing
    * Phar context options — Phar context option listing
    * Context parameters — Context parameter listing

# Supported Protocols and Wrappers

    * file:// — Accessing local filesystem
    * http:// — Accessing HTTP(s) URLs
    * ftp:// — Accessing FTP(s) URLs
    * php:// — Accessing various I/O streams
    * zlib:// — Compression Streams
    * data:// — Data (RFC 2397)
    * glob:// — Find pathnames matching pattern
    * phar:// — PHP Archive
    * ssh2:// — Secure Shell 2
    * rar:// — RAR
    * ogg:// — Audio streams
    * expect:// — Process Interaction Streams

=====================================================================


=====================================================================


=====================================================================


=====================================================================


=====================================================================


=====================================================================


=====================================================================


=====================================================================


=====================================================================