Reference — What does this symbol mean in PHP?

Question

What is this?

This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.

Why is this?

It used to be hard to find questions about operators and other syntax tokens.¹
The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the PHP Manual.

Note: Since January 2013, Stack Overflow does support special characters. Just surround the search terms by quotes, e.g. [php] "==" vs "==="

What should I do here?

If you have been pointed here by someone because you have asked such a question, please find the particular syntax below. The linked pages to the PHP manual along with the linked questions will likely answer your question then. If so, you are encouraged to upvote the answer. This list is not meant as a substitute to the help others provided.

The List

If your particular token is not listed below, you might find it in the List of Parser Tokens.

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& Bitwise Operators or References

• What does it mean to start a PHP function with an ampersand?
• Understanding PHP & (ampersand, bitwise and) operator
• PHP "&" operator
• Difference between & and && in PHP
• What does "&" mean here in PHP?
• What does "&" mean in this case?
• What does the "&" sign mean in PHP?
• What does this signature mean (&) in PHP?
• How does the "&" operator work in a PHP function?
• What does & in &2 mean in PHP?
• When should I use a bitwise operator?
• Is there ever a need to use ampersand in front of an object? (&$)

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=& References

• Reference assignment operator in PHP, =&
• What do the "=&" and "&=" operators in PHP mean?
• What do the '&=' and '=&' operators do?
• What does =& mean in PHP?

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&= Bitwise Operators

• What do the "=&" and "&=" operators in PHP mean?
• What do the '&=' and '=&' operators do?

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&& Logical Operators

• 'AND' vs '&&' as operator
• Difference between & and && in PHP
• Is there any difference between "and" and "&&" operators in PHP?
• PHP - and / or keywords

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% Arithmetic Operators

• What does the percent sign mean in PHP?
• What is the PHP operator % and how do I use it in real-world examples?

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!! Logical Operators

• Double not (!!) operator in PHP

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@ Error Control Operators

• What is the use of the @ symbol in PHP?
• 'At' symbol before variable name in PHP: @$_POST
• PHP functions and @functions
• Should I use @ in my PHP code?
• What does @ mean in PHP?

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?: Ternary Operator

• What are the PHP operators "?" and ":" called and what do they do?
• ?: operator (the 'Elvis operator') in PHP
• Where can I read about conditionals done with "?" and ":" (colon)?
• Using PHP 5.3 ?: operator

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?? Null Coalesce Operator (since PHP 7)

• C#'s null coalescing operator (??) in PHP

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?string ?int ?array ?bool ?float Nullable return type declaration (since PHP 7.1)

• Nullable return type declaration

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: Alternative syntax for control structures, Ternary Operator

• What is ":" in PHP?
• What does ":" mean in PHP?

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:: Scope Resolution Operator

• What do two colons mean in PHP?
• What's the meaning of the PHP token name T_PAAMAYIM_NEKUDOTAYIM?
• What's the difference between :: (double colon) and -> (arrow) in PHP?
• What exactly are late static bindings in PHP?
• static::staticFunctionName()
• Unexpected T_PAAMAYIM_NEKUDOTAYIM, expecting T_NS_Separator

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\ Namespaces

• Backslash in PHP -- what does it mean?
• What does a \ (backslash) do in PHP (5.3+)?

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-> Classes And Objects

• What is the "->" PHP operator called and how do you say it when reading code out loud?
• Where do we use the object operator "->" in PHP?
• What's the difference between :: (double colon) and -> (arrow) in PHP?
• What does the PHP syntax $var1->$var2 mean?
• What does "->" mean/refer to in PHP?

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=> Arrays

• What does "=>" mean in PHP?
• Use of => in PHP
• What does $k => $v in foreach($ex as $k=>$v) mean?

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^ Bitwise Operators

• How does the bitwise operator XOR ('^') work?
• What does ^ mean in PHP?

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>> Bitwise Operators

• What does >> mean in PHP?

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<< Bitwise Operators

• Strange print behaviour in PHP?

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<<< Heredoc or Nowdoc

• What does <<<END mean in PHP?
• PHP expression <<<EOB
• In PHP, what does "<<<" represent?
• Using <<<CON in PHP
• What's this kind of syntax in PHP?

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= Assignment Operators

• The 3 different equals

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== Comparison Operators

• How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?
• PHP != and == operators
• The 3 different equals
• Type-juggling and (strict) greater/lesser-than comparisons in PHP

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=== Comparison Operators

• What does "===" mean?
• How do the PHP equality (== double equals) and identity (=== triple equals) comparison operators differ?
• The 3 different equals
• Type-juggling and (strict) greater/lesser-than comparisons in PHP

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!== Comparison Operators

• What does !== comparison operator in PHP mean?
• Is there a difference between !== and != in PHP?

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!= Comparison Operators

• PHP != and == operators
• Is there a difference between !== and != in PHP?
• comparing, !== versus !=
• What is the difference between <> and !=

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<> Comparison Operators

• PHP operator <>
• PHP's <> operator
• What is the difference between <> and !=
• Type-juggling and (strict) greater/lesser-than comparisons in PHP

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<=> Comparison Operators (since PHP 7.0)

• Spaceship (three way comparison) operator

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| Bitwise Operators

• What is the difference between the | and || operators?
• What Does Using A Single Pipe '|' In A Function Argument Do?

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|| Logical Operators

• What is the difference between the | and || operators?
• PHP - and / or keywords
• What exactly does || mean?
• The behaviour of the or operator in PHP

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~ Bitwise Operators

• What does this ~ operator mean here?

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+ Arithmetic Operators, Array Operators

• + operator for array in PHP?

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+= and -= Assignment Operators

• What is += used for?
• What does `$page -= 1` in my PHP document mean?

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++ and -- Incrementing/Decrementing Operators

• Understanding Incrementing
• Answer below

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.= Assignment Operators

• What is the difference between .= and += in PHP?
• To understand a line of PHP

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. String Operators

• Difference between period and comma when concatenating with echo versus return?
• What does a . (dot) do in PHP?

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, Function Arguments

• Difference between period and comma when concatenating with echo versus return?

, Variable Declarations

• What do commas mean in a variable declaration?

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$$ Variable Variables

• What does $$ (dollar dollar or double dollar) mean in PHP?
• what is "$$" in PHP
• $function() and $$variable

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` Execution Operator

• What are the backticks `` called?

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<?= Short Open Tags

• What does this symbol mean in PHP <?=
• What does '<?=' mean in PHP?
• What does <?= mean?

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[] Arrays (short syntax since PHP 5.4)

• PHP arrays... What is/are the meaning(s) of an empty bracket?
• What is the meaning of []
• Php array_push() vs myArray[]
• What does [] mean when reading from a PHP array?
• Shorthand for arrays: literal $var = [] empty array

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<? Opening and Closing tags

• Are PHP short tags acceptable to use?

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... Argument unpacking (since PHP 5.6)

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** Exponentiation (since PHP 5.6)

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# One-line shell-style comment

• Can I use hashes for comments in PHP?

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:? Nullable return types

• php method argument type hinting with question mark (?type)

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Answer 1

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

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

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

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Stack Overflow Posts:

• Understanding Incrementing

Answer 2

Null coalescing operator (??)

This operator has been added in PHP 7.0 for the common case of needing to use a ternary operator in conjunction with isset(). It returns its first operand if it exists and is not NULL; otherwise it returns its second operand.

<?php
// Fetches the value of $_GET['user'] and returns 'nobody'
// if it does not exist.
$username = $_GET['user'] ?? 'nobody';
// This is equivalent to:
$username = isset($_GET['user']) ? $_GET['user'] : 'nobody';

// Coalescing can be chained: this will return the first
// defined value out of $_GET['user'], $_POST['user'], and
// 'nobody'.
$username = $_GET['user'] ?? $_POST['user'] ?? 'nobody';
?>

Answer 3

== is used for check equality without considering variable data-type

=== is used for check equality for both the variable value and data-type

Example

$a = 5

1. if ($a == 5) - will evaluate to true

2. if ($a == '5') - will evaluate to true, because while comparing this both value PHP internally convert that string value into integer and then compare both values

3. if ($a === 5) - will evaluate to true

4. if ($a === '5') - will evaluate to false, because value is 5, but this value 5 is not an integer.

Answer 4

Type Operators

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

<?php
class mclass { }
class sclass { }
$a = new mclass;
var_dump($a instanceof mclass);
var_dump($a instanceof sclass);

The above example will output:

bool(true)
bool(false)

Reason: Above Example $a is a object of the mclass so use only a mclass data not instance of with the sclass

Example with inheritance

<?php 
class pclass { } 
class childclass extends pclass { } 
$a = new childclass; 
var_dump($a instanceof childclass); 
var_dump($a instanceof pclass);

The above example will output:

bool(true)
bool(true)

Example with Clone

<?php 
class cloneable { } 
$a = new cloneable;
$b = clone $a; 
var_dump($a instanceof cloneable); 
var_dump($b instanceof cloneable);

The above example will output:

bool(true)
bool(true)

Answer 5

PHP Strings: PHP Strings can be specified in four ways not just two ways:

1) Single Quote Strings:

$string = 'This is my string'; // print This is my string

2) Double Quote Strings:

$str = 'string';

$string = "This is my $str"; // print This is my string

3) Heredoc:

$string = <<<EOD
This is my string
EOD; // print This is my string

4) Nowdoc (since PHP 5.3.0):

$string = <<<'END_OF_STRING'
    This is my string 
END_OF_STRING; // print This is my string

Answer 6

Magic constants: Although these are not just symbols but important part of this token family. There are eight magical constants that change depending on where they are used.

__LINE__: The current line number of the file.

__FILE__: The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances.

__DIR__: The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(__FILE__). This directory name does not have a trailing slash unless it is the root directory. (Added in PHP 5.3.0.)

__FUNCTION__: The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.

__CLASS__: The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased. The class name includes the namespace it was declared in (e.g. Foo\Bar). Note that as of PHP 5.4 __CLASS__ works also in traits. When used in a trait method, __CLASS__ is the name of the class the trait is used in.

__TRAIT__: The trait name. (Added in PHP 5.4.0) As of PHP 5.4 this constant returns the trait as it was declared (case-sensitive). The trait name includes the namespace it was declared in (e.g. Foo\Bar).

__METHOD__: The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive).

__NAMESPACE__: The name of the current namespace (case-sensitive). This constant is defined in compile-time (Added in PHP 5.3.0).

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