PHP Manual

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Chapter 10. 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 10-1. Advanced escaping

if ($expression) { 
    <strong>This is true.</strong>
} else { 
    <strong>This is false.</strong>
This works as expected, because when PHP hits the ?> closing tags, it simply starts outputting whatever it finds 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 10-2. PHP Opening and Closing Tags

1.  <?php echo 'if you want to serve XHTML or XML documents, do like this'; ?>

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

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.

Note: If you are using PHP 3 you may also enable short tags via the short_tags() function. This is only available in PHP 3!

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

Note: Support for ASP tags was added in 3.0.4.

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.

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.

    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.


PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:

    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.

    echo 'This is a test'; /* This comment will cause a problem */

Chapter 11. Types


PHP supports eight primitive types.

Four scalar types:

Two compound types:

And finally two special types:

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

You may also find some references to the type "double". Consider double the same as float, the two names exist only for historic reasons.

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

Note: If you want to check out the type and value of a certain expression, use var_dump().

Note: If you simply want a human-readable representation of the type for debugging, use gettype(). To check for a certain type, do not use gettype(), but use the is_type functions. Some examples:

$bool = TRUE;   // a boolean
$str  = "foo";  // a string
$int  = 12;     // an integer

echo gettype($bool); // prints out "boolean"
echo gettype($str);  // prints out "string"

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

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

If you would like to force a variable to be converted to a certain type, you may 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. Also, you may be interested in viewing the type comparison tables, as they show examples of various type related comparisons.


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

Note: The boolean type was introduced in PHP 4.


To specify a boolean literal, use either the keyword TRUE or FALSE. Both are case-insensitive.

$foo = True; // assign the value TRUE to $foo

Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.

// == is an operator which test
// 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 you can simply type
if ($show_separators) {
    echo "<hr>\n";

Converting to boolean

To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, 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:

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


-1 is considered TRUE, like any other non-zero (whether negative or positive) number!

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)


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

See also: Arbitrary length integer / GMP, Floating point numbers, and Arbitrary precision / BCMath


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

If you use the octal notation, you must precede the number with a 0 (zero), to use hexadecimal notation precede the number with 0x.

Example 11-1. Integer literals

$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 possible 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). PHP does not support unsigned integers.


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

Example 11-2. Octal weirdness

var_dump(01090); // 010 octal = 8 decimal

Integer overflow

If you specify a number beyond the bounds of the integer type, it will be interpreted as a float instead. Also, if you perform an operation that results in a number beyond the bounds of the integer type, a float will be returned instead.

$large_number =  2147483647;
// output: int(2147483647)

$large_number =  2147483648;
// output: float(2147483648)

// this doesn't go for hexadecimal specified integers:
var_dump( 0x100000000 );
// output: int(2147483647)

$million = 1000000;
$large_number =  50000 * $million;
// output: float(50000000000)


Unfortunately, there was a bug in PHP so that this does not always work correctly when there are negative numbers involved. For example: when you do -50000 * $million, the result will be -429496728. However, when both operands are positive there is no problem.

This is solved in PHP 4.1.0.

There is no integer division operator in PHP. 1/2 yields the float 0.5. You can cast the value to an integer to always round it downwards, or you can use the round() function.

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 the (integer) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires an integer argument. You can also convert a value to integer with the function intval().

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), the result is undefined, since the float hasn't got enough precision to give an exact integer result. No warning, not even a notice will be issued in this case!


Never cast an unknown fraction to integer, as this can sometimes lead to unexpected results.

echo (int) ( (0.1+0.7) * 10 ); // echoes 7!

See for more information the warning about float-precision.

From other types


Behaviour of converting to integer is undefined for other types. Currently, the behaviour is the same as if the value was first converted to boolean. However, do not rely on this behaviour, as it can change without notice.

Floating point numbers

Floating point numbers (AKA "floats", "doubles" or "real numbers") can be specified using any of the following syntaxes:

$a = 1.234; 
$b = 1.2e3; 
$c = 7E-10;


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 (that's 64 bit IEEE format).

Floating point precision

It is quite usual that simple decimal fractions like 0.1 or 0.7 cannot be converted into their internal binary counterparts without a little 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 as the result of the internal representation really being something like 7.9999999999....

This is related to the fact that it is impossible to exactly express some fractions in decimal notation with a finite number of digits. For instance, 1/3 in decimal form becomes 0.3333333. . ..

So never trust floating number results to the last digit and never compare floating point numbers for equality. If you really need higher precision, you should use the arbitrary precision math functions or gmp functions instead.

Converting to float

For information on when and how strings are converted to floats, see the section titled String conversion to numbers. For values of other types, the conversion is the same as if the value would have been converted to integer and then to float. See the Converting to integer section for more information. As of PHP 5, notice is thrown if you try to convert object to float.


A string is series of characters. In PHP, a character is the same as a byte, that is, there are exactly 256 different characters possible. This also implies that PHP has no native support of Unicode. See utf8_encode() and utf8_decode() for some Unicode support.

Note: It is no problem for a string to become very large. There is no practical bound to the size of strings imposed by PHP, so there is no reason at all to worry about long strings.


A string literal can be specified in three different ways.

Single quoted

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

To specify a literal single quote, you will need to escape it with a backslash (\), like in many other languages. If a backslash needs to occur before a single quote or at the end of the string, you need to double it. Note that if you try to escape any other character, the backslash will also be printed! So usually there is no need to escape the backslash itself.

Note: In PHP 3, a warning will be issued at the E_NOTICE level when this happens.

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

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 understands more escape sequences for special characters:

Table 11-1. Escaped characters

\nlinefeed (LF or 0x0A (10) in ASCII)
\rcarriage return (CR or 0x0D (13) in ASCII)
\thorizontal tab (HT or 0x09 (9) in ASCII)
\$dollar sign
\[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

Again, if you try to escape any other character, the backslash will be printed too! Before PHP 5.1.1, backslash in \{$var} hasn't been printed.

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


Another way to delimit strings is by using heredoc syntax ("<<<"). One should provide an identifier after <<<, then the string, and then the same identifier to close the quotation.

The closing identifier must begin in the first column of the line. Also, the identifier used 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.


It is very important to note that the line with the closing identifier contains 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 after or before the semicolon. It's also important to realize that the first character before the closing identifier must be a newline as defined by your operating system. This is \r on Macintosh for example.

If this rule is broken and the closing identifier is not "clean" then it's not considered to be a closing identifier and PHP will continue looking for one. If in this case a proper closing identifier is not found then a parse error will result with the line number being at the end of the script.

It is not allowed to use heredoc syntax in initializing class members. Use other string syntaxes instead.

Example 11-3. Invalid example

class foo {
    public $bar = <<<EOT

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

Example 11-4. Heredoc string quoting example

$str = <<<EOD
Example of string
spanning multiple lines
using heredoc syntax.

/* 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

Note: Heredoc support was added in PHP 4.

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 parse a variable, an array value, or an object property.

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 if you want to explicitly specify the end of the name.

$beer = 'Heineken';
echo "$beer's taste is great"; // works, "'" is an invalid character for varnames
echo "He drank some $beers";   // won't work, 's' is a valid character for varnames
echo "He drank some ${beer}s"; // works
echo "He drank some {$beer}s"; // works

Similarly, you can also have an array index or an object property parsed. With array indices, the closing square bracket (]) marks the end of the index. For object properties the same rules apply as to simple variables, though with object properties there doesn't exist a trick like the one with variables.

// These examples are specific to using arrays inside of strings.
// When outside of a string, always quote your array string keys 
// and do not use {braces} when outside of strings either.

// Let's show all errors

$fruits = array('strawberry' => 'red', 'banana' => 'yellow');

// Works but note that this works differently outside string-quotes
echo "A banana is $fruits[banana].";

// Works
echo "A banana is {$fruits['banana']}.";

// Works but PHP looks for a constant named banana first
// as described below.
echo "A banana is {$fruits[banana]}.";

// Won't work, use braces.  This results in a parse error.
echo "A banana is $fruits['banana'].";

// Works
echo "A banana is " . $fruits['banana'] . ".";

// Works
echo "This square is $square->width meters broad.";

// Won't work. For a solution, see the complex syntax.
echo "This square is $square->width00 centimeters broad.";

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 you can include complex expressions this way.

In fact, you can include any value that is in the namespace in strings with this syntax. You simply write the expression the same way as you would outside the string, and then include it in { and }. Since you can't escape '{', this syntax will only be recognised when the $ is immediately following the {. (Use "{\$" to get a literal "{$"). Some examples to make it clear:

// Let's show all errors

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

// This is wrong for the same reason as $foo[bar] is wrong 
// outside a string.  In other words, it will still work but
// because PHP first looks for a constant named foo, it will
// throw an error of level E_NOTICE (undefined constant).
echo "This is wrong: {$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 "You can even write {$obj->values[3]->name}";

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

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 in curly braces.

Note: For backwards compatibility, you can still use array-brackets for the same purpose. However, this syntax is deprecated as of PHP 4.

Example 11-5. Some string examples

// 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';

Useful functions and operators

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

There are a lot of useful functions for string modification.

See the string functions section for general functions, the regular expression functions for advanced find&replacing (in two tastes: Perl and POSIX extended).

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

Finally, if you still didn't find what you're looking for, see also the character type functions.

Converting to string

You can convert a value to a string using the (string) cast, or the strval() function. String conversion is automatically done in the scope of an expression for you where a string is needed. This happens when you use the echo() or print() functions, or when you compare a variable value to a string. Reading the manual sections on Types and Type Juggling will make the following clearer. See also settype().

A boolean TRUE value is converted to the string "1", the FALSE value is represented as "" (empty string). This way you can convert back and forth between boolean and string values.

An integer or a floating point number (float) is converted to a string representing the number with its digits (including the exponent part for floating point numbers).

Arrays are always converted to the string "Array", so you cannot dump out the contents of an array with echo() or print() to see what is inside them. To view one element, you'd do something like echo $arr['foo']. See below for tips on dumping/viewing the entire contents.

Objects are always converted to the string "Object". If you would like to print out the member variable values of an object for debugging reasons, read the paragraphs below. If you would like to find out the class name of which an object is an instance of, use get_class(). As of PHP 5, __toString() method is used if applicable.

Resources are always converted to strings with the structure "Resource id #1" where 1 is the unique number of the resource assigned by PHP during runtime. If you would like to get the type of the resource, use get_resource_type().

NULL is always converted to an empty string.

As you can see above, printing out the arrays, objects or resources does not provide you any useful information about the values themselves. Look at the functions print_r() and var_dump() for better ways to print out values for debugging.

You can also convert PHP values to strings to store them permanently. This method is called serialization, and can be done with the function serialize(). You can also serialize PHP values to XML structures, if you have WDDX support in your PHP setup.

String conversion to numbers

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

The string will evaluate as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will evaluate as an integer.

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.

$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).

If you would like to test any of the examples in this section, you can cut and paste the examples and insert the following line to see for yourself what's going on:

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 you would do in C for example). Use the functions ord() and chr() to convert between charcodes and characters.


An array in PHP is actually an ordered map. A map is a type that maps values to keys. This type is optimized in several ways, so you can use it as a real array, or a list (vector), hashtable (which is an implementation of a map), dictionary, collection, stack, queue and probably more. Because you can have another PHP array as a value, you can also quite easily simulate trees.

Explanation of those data structures is beyond the scope of this manual, but you'll find at least one example for each of them. For more information we refer you to external literature about this broad topic.


Specifying with array()

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

array( [key =>] value
     , ...
// key may be an integer or string
// value may be any value

$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. There are no different indexed and associative array types in PHP; there is only one array type, which can both contain integer and string indices.

A value can be of any PHP type.

$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 you do not specify a key for a given value, then the maximum of the integer indices is taken, and the new key will be that maximum value + 1. If you specify a key that already has a value assigned to it, that value will be overwritten.

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

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


As of PHP 4.3.0, the index generation behaviour described above has changed. Now, if you append to an array in which the current maximum key is negative, then the next key created will be zero (0). Before, the new index would have been set to the largest existing key + 1, the same as positive indices are.

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

You cannot use arrays or objects as keys. Doing so will result in a warning: Illegal offset type.

Creating/modifying with square-bracket syntax

You can also modify an existing array by explicitly setting values in it.

This is done by assigning values to the array while specifying the key in brackets. You can also omit the key, add an empty pair of brackets ("[]") to the variable name in that case.
$arr[key] = value;
$arr[] = value;
// key may be an integer or string
// value may be any value
If $arr doesn't exist yet, it will be created. So this is also an alternative way to specify an array. To change a certain value, just assign a new value to an element specified with its key. If you want to remove a key/value pair, you need to unset() it.

$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 you provide the brackets with no key specified, then the maximum of the existing integer indices is taken, and the new key will be that maximum value + 1 . If no integer indices exist yet, the key will be 0 (zero). If you specify a key that already has a value assigned to it, that value will be overwritten.


As of PHP 4.3.0, the index generation behaviour described above has changed. Now, if you append to an array in which the current maximum key is negative, then the next key created will be zero (0). Before, the new index would have been set to the largest existing key + 1, the same as positive indices are.

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

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

// Now delete every item, but leave the array itself intact:
foreach ($array as $i => $value) {

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

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

The above example will output:

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

Useful functions

There are quite a few useful functions for working with arrays. See the array functions section.

Note: The unset() function allows unsetting keys of an array. Be aware that the array will NOT be reindexed. If you only use "usual integer indices" (starting from zero, increasing by one), you can achieve the reindex effect by using array_values().

$a = array(1 => 'one', 2 => 'two', 3 => 'three');
/* 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?

You should always use quotes around a string literal array index. For example, use $foo['bar'] and not $foo[bar]. But why is $foo[bar] wrong? You might have seen the following syntax in old scripts:

$foo[bar] = 'enemy';
echo $foo[bar];
// etc

This is wrong, but it works. Then, why is it wrong? The reason is that this code has an undefined constant (bar) rather than a string ('bar' - notice the quotes), and PHP may in future define constants which, unfortunately for your 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. You do not want to quote keys which are constants or variables, as this will prevent PHP from interpreting them.

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";

Note: The above example will output:

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

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

More examples to demonstrate this fact:

// Let's show all errors

$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

// Let's define a constant to demonstrate what's going on.  We
// will assign value 'veggie' 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 error here
print "Hello $arr[fruit]";      // Hello apple

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

// This will not work, results 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 autoglobals in strings as well
print "Hello $arr['fruit']";
print "Hello $_GET['foo']";

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

When you turn error_reporting() up to show E_NOTICE level errors (such as setting it to E_ALL) then you will see these errors. By default, error_reporting is turned down to not show them.

As stated in the syntax section, there must be an expression between the square brackets ('[' and ']'). That means that you can write things like this:

echo $arr[somefunc($bar)];

This is an example of using a function return value as the array index. PHP also knows about constants, as you may have seen the E_* ones before.

$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:

$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.

As we already explained in the above examples, $foo[bar] still works but is wrong. It works, because bar is due to its syntax expected to be a constant expression. However, in this case no constant with the name bar exists. PHP now assumes that you meant bar literally, as the string "bar", but that you forgot to write the quotes.

So why is it bad then?

At some point in the future, the PHP team might want to add another constant or keyword, or you may introduce another constant into your application, and then you get in trouble. For example, you already cannot use the words empty and default this way, since they are special 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, if you convert a value to an array, you get an array with one element (with index 0), which is the scalar value you started with.

If you convert an object to an array, you get the properties (member variables) of that object as the array's elements. The keys are the member variable names.

If you convert a NULL value to an array, you get an empty array.


It is possible to compare arrays by array_diff() and by Array operators.


The array type in PHP is very versatile, so here will be some examples to show you the full power of arrays.

// this
$a = array( 'color' => 'red',
            'taste' => 'sweet',
            'shape' => 'round',
            'name'  => 'apple',
                       4        // key will be 0

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

$b[] = 'a';
$b[] = 'b';
$b[] = 'c';
// will result in the array array(0 => 'a' , 1 => 'b' , 2 => 'c'),
// or simply array('a', 'b', 'c')

Example 11-6. Using array()

// Array as (property-)map
$map = array( 'version'    => 4,
              'OS'         => 'Linux',
              'lang'       => 'english',
              'short_tags' => true
// strictly numerical keys
$array = array( 7,
// 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 11-7. Collection

$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 values of the array directly is possible since PHP 5 by passing them as reference. Prior versions need workaround:

Example 11-8. Collection

// 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);


The above example will output:

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

This example creates a one-based array.

Example 11-9. One-based index

$firstquarter  = array(1 => 'January', 'February', 'March');

The above example will output:

    [1] => 'January'
    [2] => 'February'
    [3] => 'March'

Example 11-10. Filling an array

// fill an array with all items from a directory
$handle = opendir('.');
while (false !== ($file = readdir($handle))) {
    $files[] = $file;

Arrays are ordered. You can also change the order using various sorting functions. See the array functions section for more information. You can count the number of items in an array using the count() function.

Example 11-11. Sorting an array


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

Example 11-12. Recursive and multi-dimensional arrays

$fruits = array ( "fruits"  => array ( "a" => "orange",
                                       "b" => "banana",
                                       "c" => "apple"
                  "numbers" => array ( 1,
                  "holes"   => array (      "first",
                                       5 => "second",

// 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"; 

You should be aware that array assignment always involves value copying. It also means that the internal array pointer used by current() and similar functions is reset. You need to use the reference operator to copy an array by reference.

$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


Object Initialization

To initialize an object, you use the new statement to instantiate the object to a variable.

class foo
    function do_foo()
        echo "Doing foo."; 

$bar = new foo;

For a full discussion, please read the section Classes and Objects.

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. Array converts to an object with properties named by array keys and with corresponding values. For any other value, a member variable named scalar will contain the value.

$obj = (object) 'ciao';
echo $obj->scalar;  // outputs 'ciao'


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 get_resource_type().

Converting to resource

As resource types hold special handlers to opened files, database connections, image canvas areas and the like, you cannot convert any value to a resource.

Freeing resources

Due to the reference-counting system introduced with PHP 4's Zend Engine, it is automatically detected when a resource is no longer referred to (just like Java). When this is the case, all resources that were in use for this resource are made free by the garbage collector. For this reason, it is rarely ever necessary to free the memory manually by using some free_result function.

Note: Persistent database links are special, they are not destroyed by the garbage collector. See also the section about persistent connections.


The special NULL value represents that a variable has 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().


There is only one value of type NULL, and that is the case-insensitive keyword NULL.

$var = NULL;       

See also is_null() and unset().

Pseudo-types used in this documentation


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 indicates that a parameter can be either integer or float.


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 simply passed by its name as a string. You can pass any builtin or user defined function with the exception of array(), echo(), empty(), eval(), exit(), isset(), list(), print() and unset().

A method of an instantiated object is passed as an array containing an object as the element with index 0 and a method name as the element with 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 as the element with index 0.

Example 11-13. Callback function examples

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

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

// Type 1: Simple callback

// 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 Juggling

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

An example of PHP's automatic type conversion is the addition operator '+'. If any of the operands is a float, then all 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.

$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.

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

If you would like to test any of the examples in this section, you can use the var_dump() function.

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

$a = "1";     // $a is a string
$a[0] = "f";  // What about string offsets? What happens?

Since PHP (for historical reasons) supports indexing into strings via offsets using the same syntax as array indexing, the example above leads to a problem: should $a become an array with its first element being "f", or should "f" become the first character of the string $a?

The current versions of PHP interpret the second assignment as a string offset identification, so $a becomes "f", the result of this automatic conversion however should be considered undefined. PHP 4 introduced the new curly bracket syntax to access characters in string, use this syntax instead of the one presented above:

$a    = "abc"; // $a is a string
$a{1} = "f";   // $a is now "afc"

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.

$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

Note that tabs and spaces are allowed inside the parentheses, so the following are functionally equivalent:

$foo = (int) $bar;
$foo = ( int ) $bar;

Note: Instead of casting a variable to string, you can also enclose the variable in double quotes.

$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 info, see these sections:

Chapter 12. Variables


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 ASCII characters from 127 through 255 (0x7f-0xff).

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

$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.

In PHP 3, 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.

As of PHP 4, PHP 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:

$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.

$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 - FALSE, zero, empty string or an empty array.

Example 12-1. Default values of uninitialized variables

echo ($unset_bool ? "true" : "false"); // false
$unset_int += 25; // 0 + 25 => 25
echo $unset_string . "abc"; // "" . "abc" => "abc"
$unset_array[3] = "def"; // array() + array(3 => "def") => array(3 => "def")

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.


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 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 'autoglobals' or '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.

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.

PHP Superglobals


Contains a reference to every variable which is currently available within the global scope of the script. The keys of this array are the names of the global variables. $GLOBALS has existed since PHP 3.


Variables set by the web server or otherwise directly related to the execution environment of the current script. Analogous to the old $HTTP_SERVER_VARS array (which is still available, but deprecated).


Variables provided to the script via URL query string. Analogous to the old $HTTP_GET_VARS array (which is still available, but deprecated).


Variables provided to the script via HTTP POST. Analogous to the old $HTTP_POST_VARS array (which is still available, but deprecated).


Variables provided to the script via HTTP cookies. Analogous to the old $HTTP_COOKIE_VARS array (which is still available, but deprecated).


Variables provided to the script via HTTP post file uploads. Analogous to the old $HTTP_POST_FILES array (which is still available, but deprecated). See POST method uploads for more information.


Variables provided to the script via the environment. Analogous to the old $HTTP_ENV_VARS array (which is still available, but deprecated).


Variables provided to the script via the GET, POST, and COOKIE input mechanisms, and which therefore cannot be trusted. The presence and order of variable inclusion in this array is defined according to the PHP variables_order configuration directive. This array has no direct analogue in versions of PHP prior to 4.1.0. See also import_request_variables().


Since PHP 4.3.0, FILE information from $_FILES does not exist in $_REQUEST.

Note: When running on the command line , this will not include the argv and argc entries; these are present in the $_SERVER array.


Variables which are currently registered to a script's session. Analogous to the old $HTTP_SESSION_VARS array (which is still available, but deprecated). See the Session handling functions section for more information.

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:

$a = 1;
include '';

Here the $a variable will be available within the included 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:

$a = 1; /* global scope */ 

function Test()
    echo $a; /* reference to local scope variable */ 


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 12-2. Using global

$a = 1;
$b = 2;

function Sum()
    global $a, $b;

    $b = $a + $b;

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 12-3. Using $GLOBALS instead of global

$a = 1;
$b = 2;

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

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 12-4. Example demonstrating superglobals and scope

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'];

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 12-5. Example demonstrating need for static variables

function Test()
    $a = 0;
    echo $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 12-6. Example use of static variables

function Test()
    static $a = 0;
    echo $a;

Now, 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 12-7. Static variables with recursive functions

function Test()
    static $count = 0;

    echo $count;
    if ($count < 10) {

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 12-8. Declaring static variables

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)

    echo $int;

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:

function test_global_ref() {
    global $obj;
    $obj = &new stdclass;

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


Executing this example will result in the following output:

object(stdClass)(0) {

A similar behaviour applies to the static statement. References are not stored statically:

function &get_instance_ref() {
    static $obj;

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

function &get_instance_noref() {
    static $obj;

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

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

Executing this example will result in the following output:

Static object: NULL
Static object: NULL

Static object: NULL
Static object: object(stdClass)(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:

$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.

$$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:

echo "$a ${$a}";

produces the exact same output as:

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.


Please note that variable variables cannot be used with PHP's Superglobal arrays within functions or class methods.

Variables from outside PHP

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 12-9. 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!" />

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

Example 12-10. Accessing data from a simple POST HTML form

// Available since PHP 4.1.0

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

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

// Available since PHP 3. 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, 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

As shown, before PHP 4.2.0 the default value for register_globals was on. And, in PHP 3 it was always 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 12-11. More complex form variables

if (isset($_POST['action']) && $_POST['action'] == 'submitted') {
    echo '<pre>';
    echo '<a href="'. $_SERVER['PHP_SELF'] .'">Please try again</a>';

    echo '</pre>';
} else {
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" 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="hidden" name="action" value="submitted" />
    <input type="submit" name="submit" value="submit me!" />

In PHP 3, the array form variable usage is limited to single-dimensional arrays. As of PHP 4, no such restriction applies.

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:

  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 12-12. A setcookie() example

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:
$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.

Chapter 13. 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]*

Example 13-1. Valid and invalid constant names


// 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.


You can define a constant by using the define()-function. 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.

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 13-2. Defining Constants

define("CONSTANT", "Hello world.");
echo CONSTANT; // outputs "Hello world."
echo Constant; // outputs "Constant" and issues a notice.

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 five 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:

Table 13-1. A few "magical" PHP constants

__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 whereas in older versions it contained relative path under some circumstances.
__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).

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

Chapter 14. 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:

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/FI 2, the statement '$a++' has no value (is not an expression), and thus you can't assign it or use it in any way. PHP enhances the increment/decrement capabilities by making these expressions as well, like in C. In PHP, like in C, there are two types of increment - pre-increment and post-increment. Both pre-increment and post-increment essentially increment the variable, and the effect on the variable is identical. The difference is with the value of the increment expression. Pre-increment, which is written '++$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:

$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:

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.

Chapter 15. Operators

An operator is something that you feed with one or more values (or expressions, in programming jargon) which yields another value (so that the construction itself becomes an expression). So you can think of functions or constructions that return a value (like print) as operators and those that return nothing (like echo) as any other thing.

There are three types of operators. Firstly there is the unary operator which operates on only one value, for example ! (the negation operator) or ++ (the increment operator). The second group are termed binary operators; this group contains most of the operators that PHP supports, and a list follows below in the section Operator Precedence.

The third group is the ternary operator: ?:. It should be used to select between two expressions depending on a third one, rather than to select two sentences or paths of execution. Surrounding ternary expressions with parentheses is a very good idea.

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. If operator precedence is equal, left to right associativity is used.

The following table lists the precedence of operators with the highest-precedence operators listed at the top of the table. Operators on the same line have equal precedence, in which case their associativity decides which order to evaluate them in.

Table 15-1. Operator Precedence

AssociativityOperatorsAdditional Information
non-associative++ -- increment/decrement
non-associative! ~ - (int) (float) (string) (array) (object) @ types
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
leftand logical
leftxor logical
leftor logical
left,many uses

Left associativity means that the expression is evaluated from left to right, right associativity means the opposite.

Example 15-1. Associativity

$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
Use parentheses to increase readability of the code.

Note: Although ! has a higher precedence than =, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the output from foo() is put into $a.

Arithmetic Operators

Remember basic arithmetic from school? These work just like those.

Table 15-2. Arithmetic Operators

-$aNegationOpposite of $a.
$a + $bAdditionSum of $a and $b.
$a - $bSubtractionDifference of $a and $b.
$a * $bMultiplicationProduct of $a and $b.
$a / $bDivisionQuotient of $a and $b.
$a % $bModulusRemainder of $a divided by $b.

The division operator ("/") returns a float value anytime, even if the two operands are integers (or strings that get converted to integers).

Note: Remainder $a % $b is negative for negative $a.

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:


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


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:


$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. Since PHP 4, assignment by reference has been supported, using the $var = &$othervar; syntax, but this is not possible in PHP 3. 'Assignment by reference' means that both variables end up pointing at the same data, and nothing is copied anywhere. To learn more about references, please read References explained.

Bitwise Operators

Bitwise operators allow you to turn specific bits within an integer on or off. If both the left- and right-hand parameters are strings, the bitwise operator will operate on the characters' ASCII values.

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

Table 15-3. Bitwise Operators

$a & $bAndBits that are set in both $a and $b are set.
$a | $bOrBits that are set in either $a or $b are set.
$a ^ $bXor Bits that are set in $a or $b but not both are set.
~ $aNot Bits that are set in $a are not set, and vice versa.
$a << $bShift left Shift the bits of $a $b steps to the left (each step means "multiply by two")
$a >> $bShift right Shift the bits of $a $b steps to the right (each step means "divide by two")


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.

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.

Table 15-4. Comparison Operators

$a == $bEqualTRUE if $a is equal to $b.
$a === $bIdentical TRUE if $a is equal to $b, and they are of the same type. (introduced in PHP 4)
$a != $bNot equalTRUE if $a is not equal to $b.
$a <> $bNot equalTRUE if $a is not equal to $b.
$a !== $bNot identical TRUE if $a is not equal to $b, or they are not of the same type. (introduced in PHP 4)
$a < $bLess thanTRUE if $a is strictly less than $b.
$a > $bGreater thanTRUE if $a is strictly greater than $b.
$a <= $bLess than or equal to TRUE if $a is less than or equal to $b.
$a >= $bGreater than or equal to TRUE if $a is greater than or equal to $b.

If you compare an integer with a string, the string is converted to a number. If you compare two numerical strings, they are compared as integers. These rules also apply to the switch statement.

var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true

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

For various types, comparison is done according to the following table (in order).

Table 15-5. Comparison with Various Types

Type of Operand 1Type of Operand 2Result
null or stringstringConvert NULL to "", numerical or lexical comparison
bool or nullanythingConvert to bool, FALSE < TRUE
objectobjectBuilt-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 numberstring, resource or numberTranslate strings and resources to numbers, usual math
arrayarrayArray 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)
arrayanythingarray is always greater
objectanythingobject is always greater

Example 15-2. Transcription of standard array comparison

// 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.

Ternary Operator

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

Example 15-3. Assigning a default value

 // 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.

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.

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.

/* 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.


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().

$output = `ls -al`;
echo "<pre>$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.

Table 15-6. Increment/decrement Operators

++$aPre-incrementIncrements $a by one, then returns $a.
$a++Post-incrementReturns $a, then increments $a by one.
--$aPre-decrementDecrements $a by one, then returns $a.
$a--Post-decrementReturns $a, then decrements $a by one.

Here's a simple example script:

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 Perl 'Z'+1 turns into 'AA', while in C 'Z'+1 turns into '[' ( ord('Z') == 90, ord('[') == 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.

Example 15-4. Arithmetic Operations on Character Variables

$i = 'W';
for ($n=0; $n<6; $n++) {
    echo ++$i . "\n";

The above example will output:


Incrementing or decrementing booleans has no effect.

Logical Operators

Table 15-7. Logical Operators

$a and $bAndTRUE if both $a and $b are TRUE.
$a or $bOrTRUE if either $a or $b is TRUE.
$a xor $bXorTRUE if either $a or $b is TRUE, but not both.
! $aNotTRUE if $a is not TRUE.
$a && $bAndTRUE if both $a and $b are TRUE.
$a || $bOrTRUE 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.)

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.

$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

Table 15-8. Array Operators

$a + $bUnionUnion of $a and $b.
$a == $bEqualityTRUE if $a and $b have the same key/value pairs.
$a === $bIdentityTRUE if $a and $b have the same key/value pairs in the same order and of the same types.
$a != $bInequalityTRUE if $a is not equal to $b.
$a <> $bInequalityTRUE if $a is not equal to $b.
$a !== $bNon-identityTRUE if $a is not identical to $b.

The + operator appends the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

$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";

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

When executed, this script will print the following:
Union of $a and $b:
array(3) {
  string(5) "apple"
  string(6) "banana"
  string(6) "cherry"
Union of $b and $a:
array(3) {
  string(4) "pear"
  string(10) "strawberry"
  string(6) "cherry"

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

Example 15-5. Comparing arrays

$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

PHP has a single type operator: instanceof is used to determine whether a given object, his parents or their implemented interfaces are of a specified object class.

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.

class A { }
class B { }

$thing = new A;

if ($thing instanceof A) {
    echo 'A';
if ($thing instanceof B) {
    echo 'B';

As $thing is an object of type A, but not B, only the block dependent on the A type will be executed:


See also get_class() and is_a().

Chapter 16. Control Structures

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.


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)

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:

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:

if ($a > $b) {
    echo "a is bigger than b";
    $b = $a;

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


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 bigger than b if $a is bigger than $b, and a is NOT bigger than b otherwise:

if ($a > $b) {
    echo "a is bigger than b";
} else {
    echo "a is NOT bigger 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, 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:

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.

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:

if ($a == 5):
    echo "a equals 5";
    echo "...";
elseif ($a == 6):
    echo "a equals 6";
    echo "!!!";
    echo "a is neither 5 nor 6";

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


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)

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):

The following examples are identical, and both print numbers from 1 to 10:

/* 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;


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's 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:

$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:

do {
    if ($i < 5) {
        echo "i is not big enough";
    $i *= $factor;
    if ($i < $minimum_limit) {
   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'.


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)

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. 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 numbers from 1 to 10:

/* example 1 */

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

/* example 2 */

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

/* example 3 */

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

/* example 4 */

for ($i = 1; $i <= 10; 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):


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

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. Therefore, the array pointer is not modified as with the each() construct, and changes to the array element returned are not reflected in the original array. However, the internal pointer of the original array is advanced with the processing of the array. Assuming the foreach loop runs to completion, the array's internal pointer will be at the end of the array.

As of PHP 5, you can easily modify array's elements by preceding $value with &. This will assign reference instead of copying the value.

$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
    $value = $value * 2;
// $arr is now array(2, 4, 6, 8)

This is possible only if iterated array can be referenced (i.e. is variable).

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

You may have noticed that the following are functionally identical:

$arr = array("one", "two", "three");
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:

$arr = array("one", "two", "three");
while (list($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:

/* 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 key printed for illustration) */

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

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

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

/* 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 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.

$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. */


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.

while (list($key, $value) = each($arr)) {
    if (!($key % 2)) { // skip odd members

$i = 0;
while ($i++ < 5) {
    echo "Outer<br />\n";
    while (1) {
        echo "&nbsp;&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.

  for ($i = 0; $i < 5; ++$i) {
      if ($i == 2)
      print "$i\n";

One can expect the result to be :


but this script will output :


because the return value of the print() call is int(1), and it will look like the optional numeric argument mentioned above.


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.

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 16-1. switch structure

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";
case 1:
    echo "i equals 1";
case 2:
    echo "i equals 2";

Example 16-2. switch structure allows usage of strings

switch ($i) {
case "apple":
    echo "i is apple";
case "bar":
    echo "i is bar";
case "cake":
    echo "i is cake";

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:

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.

switch ($i) {
case 0:
case 1:
case 2:
    echo "i is less than 3 but not negative";
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, and should be the last case statement. For example:

switch ($i) {
case 0:
    echo "i equals 0";
case 1:
    echo "i equals 1";
case 2:
    echo "i equals 2";
    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 .

switch ($i):
case 0:
    echo "i equals 0";
case 1:
    echo "i equals 1";
case 2:
    echo "i equals 2";
    echo "i is not equal to 0, 1 or 2";


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)

The directive section allows the behavior of the declare block to be set. Currently only one directive is recognized: the ticks directive. (See below for more information on the ticks directive)

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.

// these are the same:

// you can use this:
declare(ticks=1) {
    // entire script here

// or you can use this:
// entire script here


A tick is an event that occurs for every N low-level 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.

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 16-3. Profile a section of PHP code

// A function that records the time when it is called
function profile($dump = FALSE)
    static $profile;

    // Return the times stored in profile, then erase it
    if ($dump) {
        $temp = $profile;
        return $temp;

    $profile[] = microtime();

// Set up a tick handler

// Initialize the function before the declare block

// Run a block of code, throw a tick every 2nd statement
declare(ticks=2) {
    for ($x = 1; $x < 50; ++$x) {
        echo similar_text(md5($x), md5($x*$x)), "<br />;";

// Display the data stored in the profiler
The example profiles the PHP code within the 'declare' block, recording the time at which every second low-level statement in the block was executed. This information can then be used to find the slow areas within particular segments of code. This process can be performed using other methods: using ticks is more convenient and easier to implement.

Ticks are well suited for debugging, implementing simple multitasking, background I/O and many other tasks.

See also register_tick_function() and unregister_tick_function().


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 only required if the argument contains an expression. It is common to leave them out while returning a variable, and you actually should as PHP has less work to do in this case.

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).


The require() statement includes and evaluates the specific file.

require() includes and evaluates a specific file. Detailed information on how this inclusion works is described in the documentation for include().

require() and include() are identical in every way except how they handle failure. include() produces a Warning while require() results in a Fatal Error. In other words, don't hesitate to use require() if you want a missing file to halt processing of the page. include() does not behave this way, the script will continue regardless. Be sure to have an appropriate include_path setting as well.

Example 16-4. Basic require() examples


require 'prepend.php';

require $somefile;

require ('somefile.txt');


See the include() documentation for more examples.

Note: Prior to PHP 4.0.2, the following applies: require() will always attempt to read the target file, even if the line it's on never executes. The conditional statement won't affect require(). However, if the line on which the require() occurs is not executed, neither will any of the code in the target file be executed. Similarly, looping structures do not affect the behaviour of require(). Although the code contained in the target file is still subject to the loop, the require() itself happens only once.

Note: Because this is a language construct and not a function, it cannot be called using variable functions


Windows versions of PHP prior to PHP 4.3.0 do not support accessing remote files via this function, even if allow_url_fopen is enabled.

See also include(), require_once(), include_once(), get_included_files(), eval(), file(), readfile(), virtual() and include_path.


The include() statement includes and evaluates the specified file.

The documentation below also applies to require(). The two constructs are identical in every way except how they handle failure. include() produces a Warning while require() results in a Fatal Error. In other words, use require() if you want a missing file to halt processing of the page. include() does not behave this way, the script will continue regardless. Be sure to have an appropriate include_path setting as well. Be warned that parse error in included file doesn't cause processing halting in PHP versions prior to PHP 4.3.5. Since this version, it does.

Files for including are first looked in include_path relative to the current working directory and then in include_path relative to the directory of current script. E.g. if your include_path is ., current working directory is /www/, you included include/a.php and there is include "b.php" in that file, b.php is first looked in /www/ and then in /www/include/. If filename begins with ./ or ../, it is looked only in include_path relative to the current working directory.

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 16-5. Basic include() example


$color = 'green';
$fruit = 'apple';



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.

Example 16-6. Including within functions


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 Appendix M 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.


Windows versions of PHP prior to PHP 4.3.0 do not support accessing remote files via this function, even if allow_url_fopen is enabled.

Example 16-7. include() through HTTP


/* This example assumes that 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 as PHP
include '';

// 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 '';

$foo = 1;
$bar = 2;
include 'file.txt';  // Works.
include 'file.php';  // Works.


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.

Because include() and require() are special language constructs, you must enclose them within a statement block if it's inside a conditional block.

Example 16-8. include() and conditional blocks


// This is WRONG and will not work as desired.
if ($condition)
    include $file;
    include $other;

// This is CORRECT.
if ($condition) {
    include $file;
} else {
    include $other;


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 16-9. Comparing return value of include

// 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';

Note: In PHP 3, the return may not appear inside a block unless it's a function block, in which case the return() applies to that function and not the whole file.

Example 16-10. include() and the return() statement


$var = 'PHP';

return $var;



$var = '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 16-11. Using output buffering to include a PHP file into a string

$string = get_include_contents('somefile.php');

function get_include_contents($filename) {
    if (is_file($filename)) {
        include $filename;
        $contents = ob_get_contents();
        return $contents;
    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.


The require_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the require() statement, with the only difference being that if the code from a file has already been included, it will not be included again. See the documentation for require() for more information on how this statement works.

require_once() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc.

For examples on using require_once() and include_once(), look at the PEAR code included in the latest PHP source code distributions.

Return values are the same as with include(). If the file was already included, this function returns TRUE

Note: require_once() was added in PHP 4.0.1pl2

Note: Be aware, that the behaviour of require_once() and include_once() may not be what you expect on a non case sensitive operating system (such as Windows).

Example 16-12. require_once() is case insensitive on Windows

require_once("a.php"); // this will include a.php
require_once("A.php"); // this will include a.php again on Windows! (PHP 4 only)
This behaviour changed in PHP 5 - 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 required just once.


Windows versions of PHP prior to PHP 4.3.0 do not support accessing remote files via this function, even if allow_url_fopen is enabled.

See also require(), include(), include_once(), get_required_files(), get_included_files(), readfile(), and virtual().


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() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc.

For more examples on using require_once() and include_once(), look at the PEAR code included in the latest PHP source code distributions.

Return values are the same as with include(). If the file was already included, this function returns TRUE

Note: include_once() was added in PHP 4.0.1pl2

Note: Be aware, that the behaviour of include_once() and require_once() may not be what you expect on a non case sensitive operating system (such as Windows).

Example 16-13. include_once() is case insensitive on Windows

include_once("a.php"); // this will include a.php
include_once("A.php"); // this will include a.php again on Windows! (PHP 4 only)
This behaviour changed in PHP 5 - 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.


Windows versions of PHP prior to PHP 4.3.0 do not support accessing remote files via this function, even if allow_url_fopen is enabled.

See also include(), require(), require_once(), get_required_files(), get_included_files(), readfile(), and virtual().


Mehdi Achour
Friedhelm Betz
Antony Dovgal
Nuno Lopes
Philip Olson
Georg Richter
Damien Seguy
Jakub Vrana
And several others

Edited by

Gabor Hojtsy



Copyright © 1997 - 2006 by the PHP Documentation Group. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later. A copy of the Open Publication License is distributed with this manual, the latest version is presently available at

Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder.

Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.

In case you are interested in redistribution or republishing of this document in whole or in part, either modified or unmodified, and you have questions, please contact the copyright holders at Note that this address is mapped to a publicly archived mailing list.

The Chapter 46 section of the documentation is based on an initial contribution by Zend Technologies.

Table of Contents
Authors and Contributors
I. Getting Started
1. Introduction
2. A simple tutorial
II. Installation and Configuration
3. General Installation Considerations
4. Installation on Unix systems
5. Installation on Mac OS X
6. Installation on Windows systems
7. Installation of PECL extensions
8. Problems?
9. Runtime Configuration
III. Language Reference
10. Basic syntax
11. Types
12. Variables
13. Constants
14. Expressions
15. Operators
16. Control Structures
17. Functions
18. Classes and Objects (PHP 4)
19. Classes and Objects (PHP 5)
20. Exceptions
21. References Explained
IV. Security
22. Introduction
23. General considerations
24. Installed as CGI binary
25. Installed as an Apache module
26. Filesystem Security
27. Database Security
28. Error Reporting
29. Using Register Globals
30. User Submitted Data
31. Magic Quotes
32. Hiding PHP
33. Keeping Current
V. Features
34. HTTP authentication with PHP
35. Cookies
36. Sessions
37. Dealing with XForms
38. Handling file uploads
39. Using remote files
40. Connection handling
41. Persistent Database Connections
42. Safe Mode
43. Using PHP from the command line
VI. Function Reference
I. .NET Functions
II. Apache-specific Functions
III. Alternative PHP Cache
IV. Advanced PHP debugger
V. Array Functions
VI. Aspell functions [deprecated]
VII. BCMath Arbitrary Precision Mathematics Functions
VIII. PHP bytecode Compiler
IX. Bzip2 Compression Functions
X. Calendar Functions
XI. CCVS API Functions [deprecated]
XII. Class/Object Functions
XIII. Classkit Functions
XIV. ClibPDF Functions
XV. COM and .Net (Windows)
XVI. Crack Functions
XVII. Character Type Functions
XVIII. CURL, Client URL Library Functions
XIX. Cybercash Payment Functions
XX. Credit Mutuel CyberMUT functions
XXI. Cyrus IMAP administration Functions
XXII. Date and Time Functions
XXIII. DB++ Functions
XXIV. Database (dbm-style) Abstraction Layer Functions
XXV. dBase Functions
XXVI. DBM Functions [deprecated]
XXVII. dbx Functions
XXVIII. Direct IO Functions
XXIX. Directory Functions
XXX. DOM Functions
XXXI. DOM XML Functions
XXXII. Error Handling and Logging Functions
XXXIII. Exif Functions
XXXIV. Expect Functions
XXXV. File Alteration Monitor Functions
XXXVI. Forms Data Format Functions
XXXVII. filePro Functions
XXXVIII. Filesystem Functions
XXXIX. Firebird/InterBase Functions
XL. Firebird/Interbase Functions (PDO_FIREBIRD)
XLI. FriBiDi Functions
XLII. FrontBase Functions
XLIII. FTP Functions
XLIV. Function Handling Functions
XLV. Gettext
XLVI. GMP Functions
XLVII. gnupg Functions
XLVIII. Net_Gopher
XLIX. hash Functions
L. HTTP Functions
LI. Hyperwave Functions
LII. Hyperwave API Functions
LIII. IBM DB2, Cloudscape and Apache Derby Functions
LIV. ICAP Functions [deprecated]
LV. iconv Functions
LVI. ID3 Functions
LVII. IIS Administration Functions
LVIII. Image Functions
LIX. IMAP, POP3 and NNTP Functions
LX. Informix Functions
LXI. Informix Functions (PDO_INFORMIX)
LXII. Ingres II Functions
LXIII. IRC Gateway Functions
LXIV. PHP / Java Integration
LXVI. LDAP Functions
LXVII. libxml Functions
LXVIII. Lotus Notes Functions
LXIX. LZF Functions
LXX. Mail Functions
LXXI. mailparse Functions
LXXII. Mathematical Functions
LXXIII. MaxDB PHP Extension
LXXIV. MCAL Functions
LXXV. Mcrypt Encryption Functions
LXXVI. MCVE (Monetra) Payment Functions
LXXVII. Memcache Functions
LXXVIII. Mhash Functions
LXXIX. Mimetype Functions
LXXX. Ming functions for Flash
LXXXI. Miscellaneous Functions
LXXXII. mnoGoSearch Functions
LXXXIII. Microsoft SQL Server Functions
LXXXIV. Microsoft SQL Server and Sybase Functions (PDO_DBLIB)
LXXXV. Mohawk Software Session Handler Functions
LXXXVI. mSQL Functions
LXXXVII. Multibyte String Functions
LXXXVIII. muscat Functions
LXXXIX. MySQL Functions
XC. MySQL Functions (PDO_MYSQL)
XCI. MySQL Improved Extension
XCII. Ncurses Terminal Screen Control Functions
XCIII. Network Functions
XCIV. Newt Functions
XCV. NSAPI-specific Functions
XCVI. Object Aggregation/Composition Functions
XCVII. Object property and method call overloading
XCVIII. Oracle functions
XCIX. ODBC Functions (Unified)
C. ODBC and DB2 Functions (PDO_ODBC)
CI. oggvorbis
CII. OpenAL Audio Bindings
CIII. OpenSSL Functions
CIV. Oracle Functions [deprecated]
CV. Oracle Functions (PDO_OCI)
CVI. Output Control Functions
CVII. Ovrimos SQL Functions
CVIII. Paradox File Access
CIX. Parsekit Functions
CX. Process Control Functions
CXI. Regular Expression Functions (Perl-Compatible)
CXII. PDF Functions
CXIII. PDO Functions
CXIV. PHP Options&Information
CXV. POSIX Functions
CXVI. Regular Expression Functions (POSIX Extended)
CXVII. PostgreSQL Functions
CXVIII. PostgreSQL Functions (PDO_PGSQL)
CXIX. Printer Functions
CXX. Program Execution Functions
CXXI. PostScript document creation
CXXII. Pspell Functions
CXXIII. qtdom Functions
CXXIV. Radius
CXXV. Rar Functions
CXXVI. GNU Readline
CXXVII. GNU Recode Functions
CXXVIII. RPM Header Reading Functions
CXXIX. runkit Functions
CXXX. Satellite CORBA client extension [deprecated]
CXXXI. SDO Functions
CXXXII. SDO XML Data Access Service Functions
CXXXIII. SDO Relational Data Access Service Functions
CXXXIV. Semaphore, Shared Memory and IPC Functions
CXXXV. SESAM Database Functions
CXXXVI. PostgreSQL Session Save Handler
CXXXVII. Session Handling Functions
CXXXVIII. Shared Memory Functions
CXXXIX. SimpleXML functions
CXL. SNMP Functions
CXLI. SOAP Functions
CXLII. Socket Functions
CXLIII. Standard PHP Library (SPL) Functions
CXLIV. SQLite Functions
CXLV. SQLite Functions (PDO_SQLITE)
CXLVI. Secure Shell2 Functions
CXLVII. Statistics Functions
CXLVIII. Stream Functions
CXLIX. String Functions
CL. Shockwave Flash Functions
CLI. Sybase Functions
CLII. TCP Wrappers Functions
CLIII. Tidy Functions
CLIV. Tokenizer Functions
CLV. Unicode Functions
CLVI. URL Functions
CLVII. Variable Handling Functions
CLVIII. Verisign Payflow Pro Functions
CLIX. vpopmail Functions
CLX. W32api Functions
CLXI. WDDX Functions
CLXII. win32ps Functions
CLXIII. win32service Functions
CLXIV. xattr Functions
CLXV. xdiff Functions
CLXVI. XML Parser Functions
CLXVIII. XMLReader functions
CLXIX. xmlwriter Functions
CLXX. XSL functions
CLXXI. XSLT Functions
CLXXII. YAZ Functions
CLXXIV. Zip File Functions (Read Only Access)
CLXXV. Zlib Compression Functions
VII. PHP and Zend Engine Internals
44. Streams API for PHP Extension Authors
45. PDO Driver How-To
46. Zend API: Hacking the Core of PHP
48. Extending PHP 3
VIII. FAQ: Frequently Asked Questions
49. General Information
50. Mailing lists
51. Obtaining PHP
52. Database issues
53. Installation FAQ
54. Build Problems
55. Using PHP
56. PHP and HTML
57. PHP and COM
58. PHP and other languages
59. Migrating from PHP 2 to PHP 3
60. Migrating from PHP 3 to PHP 4
61. Migrating from PHP 4 to PHP 5
62. Miscellaneous Questions
IX. Appendixes
A. History of PHP and related projects
B. Migrating from PHP 4 to PHP 5
C. Migrating from PHP 3 to PHP 4
D. Migrating from PHP/FI 2 to PHP 3
E. Debugging PHP
F. Configure options
G. php.ini directives
H. List of Supported Timezones
I. Extension Categorization
J. List of Function Aliases
K. List of Reserved Words
L. List of Resource Types
M. List of Supported Protocols/Wrappers
N. List of Available Filters
O. List of Supported Socket Transports
P. PHP type comparison tables
Q. List of Parser Tokens
R. About the manual
S. Open Publication License
T. Function Index