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

{} Curly braces

• Blocks - curly braces/no curly braces?
• Curly braces in string in PHP
• PHP curly braces in array notation

And some words about last post

$x[4] = 'd'; // it works
$x{4} = 'd'; // it works

$echo $x[4]; // it works
$echo $x{4}; // it works

$x[] = 'e'; // it works
$x{} = 'e'; // does not work

$x = [1, 2]; // it works
$x = {1, 2}; // does not work

echo "${x[4]}"; // it works
echo "${x{4}}"; // does not work

echo "{$x[4]}"; // it works
echo "{$x{4}}"; // it works

Answer 2

Question:

What does "&" mean here in PHP?

PHP "&" operator

Makes life more easier once we get used to it..(check example below carefully)

& usually checks bits that are set in both $a and $b are set.

have you even noticed how these calls works?

   error_reporting(E_ERROR | E_WARNING | E_PARSE);
    error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);
    error_reporting(E_ALL & ~E_NOTICE);
    error_reporting(E_ALL);

So behind all above is game of bitwise operator and bits.

One usefull case of these is easy configurations like give below, so a single integer field can store thousands of combos for you.

Most people have already read the docs but didn't reliase the real world use case of these bitwise operators.

Example That you 'll love

<?php

class Config {

    // our constants must be 1,2,4,8,16,32,64 ....so on
    const TYPE_CAT=1;
    const TYPE_DOG=2;
    const TYPE_LION=4;
    const TYPE_RAT=8;
    const TYPE_BIRD=16;
    const TYPE_ALL=31;

    private $config;

    public function __construct($config){
        $this->config=$config;

        if($this->is(Config::TYPE_CAT)){
            echo 'cat ';
        }
        if($this->is(Config::TYPE_DOG)){
            echo 'dog ';
        }
        if($this->is(Config::TYPE_RAT)){
            echo 'rat ';
        }
        if($this->is(Config::TYPE_LION)){
            echo 'lion ';
        }
        if($this->is(Config::TYPE_BIRD)){
            echo 'bird ';
        }
        echo "\n";
    }

    private function is($value){
        return $this->config & $value;
    }
}

new Config(Config::TYPE_ALL);
// cat dog rat lion bird
new Config(Config::TYPE_BIRD);
//bird
new Config(Config::TYPE_BIRD | Config::TYPE_DOG);
//dog bird
new Config(Config::TYPE_ALL & ~Config::TYPE_DOG & ~Config::TYPE_CAT);
//rat lion bird

Answer 3

<=> Spaceship Operator

Added in PHP 7

The spaceship operator <=> is the latest comparison operator added in PHP 7. It is a non-associative binary operator with the same precedence as equality operators (==, !=, ===, !==). This operator allows for simpler three-way comparison between left-hand and right-hand operands.

The operator results in an integer expression of:

• 0 when both operands are equal
• Less than 0 when the left-hand operand is less than the right-hand operand
• Greater than 0 when the left-hand operand is greater than the right-hand operand

e.g.

1 <=> 1; // 0
1 <=> 2; // -1
2 <=> 1; // 1

A good practical application of using this operator would be in comparison type callbacks that are expected to return a zero, negative, or positive integer based on a three-way comparison between two values. The comparison function passed to usort is one such example.

Before PHP 7 you would write...

$arr = array(4,2,1,3);

usort($arr, function ($a, $b) {
    if ($a < $b) {
        return -1;
    } elseif ($a > $b) {
        return 1;
    } else {
        return 0;
    }
});

Since PHP 7 you can write...

$arr = [4,2,1,3];

usort($arr, function ($a, $b) {
    return $a <=> $b;
});

Answer 4

Null Coalesce operator "??" (Added in PHP 7)

Not the catchiest name for an operator, but PHP 7 brings in the rather handy null coalesce so I thought I'd share an example.

In PHP 5, we already have a ternary operator, which tests a value, and then returns the second element if that returns true and the third if it doesn't:

echo $count ? $count : 10; // outputs 10

There is also a shorthand for that which allows you to skip the second element if it's the same as the first one: echo $count ?: 10; // also outputs 10

In PHP 7 we additionally get the ?? operator which rather than indicating extreme confusion which is how I would usually use two question marks together instead allows us to chain together a string of values. Reading from left to right, the first value which exists and is not null is the value that will be returned.

// $a is not set
$b = 16;

echo $a ?? 2; // outputs 2
echo $a ?? $b ?? 7; // outputs 16

This construct is useful for giving priority to one or more values coming perhaps from user input or existing configuration, and safely falling back on a given default if that configuration is missing. It's kind of a small feature but it's one that I know I'll be using as soon as my applications upgrade to PHP 7.

Answer 5

Nullable return type declaration

PHP 7 adds support for return type declarations. Similarly to argument type declarations, return type declarations specify the type of value that will be returned from a function. The same types are available for return type declarations as are available for argument type declarations.

Strict typing also has an effect on return type declarations. In the default weak mode, returned values will be coerced to the correct type if they are not already of that type. In strong mode, the returned value must be of the correct type, otherwise, a TypeError will be thrown.

As of PHP 7.1.0, return values can be marked as nullable by prefixing the type name with a question mark (?). This signifies that the function returns either the specified type or NULL.

<?php
function get_item(): ?string {
    if (isset($_GET['item'])) {
        return $_GET['item'];
    } else {
        return null;
    }
}
?>

Source

Answer 6

An overview of operators in PHP:

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Logical Operators:

• $a && $b : TRUE if both $a and $b are TRUE.
• $a || $b : TRUE if either $a or $b is TRUE.
• $a xor $b : TRUE if either $a or $b is TRUE, but not both.
• ! $a : TRUE if $a is not TRUE.
• $a and $b : TRUE if both $a and $b are TRUE.
• $a or $b : TRUE if either $a or $b is TRUE.

---

Comparison operators:

• $a == $b : TRUE if $a is equal to $b after type juggling.
• $a === $b : TRUE if $a is equal to $b, and they are of the same type.
• $a != $b : TRUE if $a is not equal to $b after type juggling.
• $a <> $b : TRUE if $a is not equal to $b after type juggling.
• $a !== $b : TRUE if $a is not equal to $b, or they are not of the same type.
• $a < $b : TRUE if $a is strictly less than $b.
• $a > $b : TRUE if $a is strictly greater than $b.
• $a <= $b : TRUE if $a is less than or equal to $b.
• $a >= $b : TRUE if $a is greater than or equal to $b.
• $a <=> $b : An integer less than, equal to, or greater than zero when $a is respectively less than, equal to, or greater than $b. Available as of PHP 7.
• $a ? $b : $c : if $a return $b else return $c (ternary operator)
• $a ?? $c : Same as $a ? $a : $c (null coalescing operator - requires PHP>=7)

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Arithmetic Operators:

• -$a : Opposite of $a.
• $a + $b : Sum of $a and $b.
• $a - $b : Difference of $a and $b.
• $a * $b : Product of $a and $b.
• $a / $b : Quotient of $a and $b.
• $a % $b : Remainder of $a divided by $b.
• $a ** $b : Result of raising $a to the $b'th power (introduced in PHP 5.6)

---

Incrementing/Decrementing Operators:

• ++$a : Increments $a by one, then returns $a.
• $a++ : Returns $a, then increments $a by one.
• --$a : Decrements $a by one, then returns $a.
• $a-- : Returns $a, then decrements $a by one.

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Bitwise Operators:

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

---

String Operators:

• $a . $b : Concatenation of $a and $b.

---

Array Operators:

• $a + $b : Union of $a and $b.
• $a == $b : TRUE if $a and $b have the same key/value pairs.
• $a === $b : TRUE if $a and $b have the same key/value pairs in the same order and of the same types.
• $a != $b : TRUE if $a is not equal to $b.
• $a <> $b : TRUE if $a is not equal to $b.
• $a !== $b : TRUE if $a is not identical to $b.

---

Assignment Operators:

• $a = $b : The value of $b is assigned to $a
• $a += $b : Same as $a = $a + $b
• $a -= $b : Same as $a = $a - $b
• $a *= $b : Same as $a = $a * $b
• $a /= $b : Same as $a = $a / $b
• $a %= $b : Same as $a = $a % $b
• $a **= $b : Same as $a = $a ** $b
• $a .= $b : Same as $a = $a . $b
• $a &= $b : Same as $a = $a & $b
• $a |= $b : Same as $a = $a | $b
• $a ^= $b : Same as $a = $a ^ $b
• $a <<= $b : Same as $a = $a << $b
• $a >>= $b : Same as $a = $a >> $b

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Note

and operator and or operator have lower precedence than assignment operator =.

This means that $a = true and false; is equivalent to ($a = true) and false.

In most cases you will probably want to use && and ||, which behave in a way known from languages like C, Java or JavaScript.