Reference - What does this symbol mean in PHP?

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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.

¹ 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.


& Bitwise Operators or References


=& References


&= Bitwise Operators


&& Logical Operators


% Arithmetic Operators


!! Logical Operators


@ Error Control Operators


?: Ternary Operator


?? Null Coalesce Operator (since PHP 7)


: Alternative syntax for control structures, Ternary Operator


:: Scope Resolution Operator


\ Namespaces


-> Classes And Objects


=> Arrays


^ Bitwise Operators


>> Bitwise Operators


<< Bitwise Operators


<<< Heredoc or Nowdoc


= Assignment Operators


== Comparison Operators


=== Comparison Operators


!== Comparison Operators


!= Comparison Operators


<> Comparison Operators


<=> Comparison Operators (since PHP 7.0)


| Bitwise Operators


|| Logical Operators


~ Bitwise Operators


+ Arithmetic Operators, Array Operators


+= and -= Assignment Operators


++ and -- Incrementing/Decrementing Operators


.= Assignment Operators


. String Operators


, Function Arguments

, Variable Declarations


$$ Variable Variables


` Execution Operator


<?= Short Open Tags


[] Arrays (since PHP 5.4)


<? Opening and Closing tags


... Argument unpacking (since PHP 5.6)


** Exponentiation (since PHP 5.6)


# One-line shell-style comment


This Question Has 15 Answeres | Orginal Question | Gordon

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'; ?> 
syntax name description x == y Equality True if x and y have the same key/value pairs x != y Inequality True if x is not equal to y x === y Identity True if x and y have the same key/value pairs in the same order and of the same types x !== y Non-identity True if x is not identical to y ++ x Pre-increment Increments x by one, then returns x x ++ Post-increment Returns x, then increments x by one -- x Pre-decrement Decrements x by one, then returns x x -- Post-decrement Returns x, then decrements x by one x and y And True if both x and y are true x=6 y=3 (x < 10 and y > 1) returns true x && y And True if both x and y are true x=6 y=3 (x < 10 && y > 1) returns true a . b Concatenation Concatenate two strings: "Hi" . "Ha" 

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) 

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 

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).

Source

QUESTION:

What does => mean?


ANSWER:

=> Is the symbol we humans decided to use to separate "Key" => "Value" pairs in Associative Arrays.

ELABORATING:

To understand this, we have to know what Associative Arrays are. The first thing that comes up when a conventional programmer thinks of an array (in PHP) would be something similar to:

$myArray1 = array(2016, "hello", 33);//option 1 $myArray2 = [2016, "hello", 33];//option 2 $myArray3 = [];//option 3 $myArray3[] = 2016; $myArray3[] = "hello"; $myArray3[] = 33; 

Where, if wanted to call the array in some later part of the code, we could do:

echo $myArray1[1];// output: hello echo $myArray2[1];// output: hello echo $myArray3[1];// output: hello 

So far so good. However, as humans, we might find it hard to remember that index [0] of the array is the value of the year 2016, index [1] of the array is a greetings, and index [2] of the array is a simple integer value. The alternative we would then have is to use what is called an Associative Array. An Associative array has a few differences from a Sequential Array (which is what the previous cases were since they increment the index used in a predetermined sequence, by incrementing by 1 for each following value).

Differences (between a sequential and associative array):

  • Durring the declaration of an Associative Array, you don't only include the value of what you want to put in the array, but you also put the index value (called the key) which you want to use when calling the array in later parts of the code. The following syntax is used during it's declaration: "key" => "value".

  • When using the Associative Array, the key value would then be placed inside the index of the array to retrieve the desired value.

For instance:

 $myArray1 = array( "Year" => 2016, "Greetings" => "hello", "Integer_value" => 33);//option 1 $myArray2 = [ "Year" => 2016, "Greetings" => "hello", "Integer_value" => 33];//option 2 $myArray3 = [];//option 3 $myArray3["Year"] = 2016; $myArray3["Greetings"] = "hello"; $myArray3["Integer_value"] = 33; 

And now, to receive the same output as before, the key value would be used in the arrays index:

echo $myArray1["Greetings"];// output: hello echo $myArray2["Greetings"];// output: hello echo $myArray3["Greetings"];// output: hello 

FINAL POINT:

So from the above example, it is pretty easy to see that the => symbol is used to express the relationship of an Associative Array between each of the key and value pairs in an array DURING the initiation of the values within the array.

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.


Stack Overflow Posts:

<=> 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...

$arr = [4,2,1,3]; usort($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; }); 

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 

Null Coalesce Operator php

The null coalescing operator (??) has been added to PHP7 for the common case of needing to use a ternary in conjunction with isset(). It returns its first operand if it exists and is not NULL otherwise it returns its second operand, such as following example:

$username = $_GET['user'] ?? 'nobody'; // This is equivalent to: $username = isset($_GET['user']) ? $_GET['user'] : 'nobody'; 

Bitwise Operator

What is a bit? A bit is a representation of 1 or 0. Basically OFF(0) and ON(1)

What is a byte? A byte is made up of 8 bits and the highest value of a byte is 255, which would mean every bit is set. We will look at why a byte's maximum value is 255.

------------------------------------------- | 1 Byte ( 8 bits ) | ------------------------------------------- |Place Value | 128| 64| 32| 16| 8| 4| 2| 1| ------------------------------------------- 

This representation of 1 Byte

1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 (1 Byte)

A few examples for better understanding

The "AND" operator: &

$a = 9; $b = 10; echo $a & $b; 

This would output the number 8. Why? Well let's see using our table example.

------------------------------------------- | 1 Byte ( 8 bits ) | ------------------------------------------- |Place Value | 128| 64| 32| 16| 8| 4| 2| 1| ------------------------------------------- | $a | 0| 0| 0| 0| 1| 0| 0| 1| ------------------------------------------- | $b | 0| 0| 0| 0| 1| 0| 1| 0| ------------------------------------------- | & | 0| 0| 0| 0| 1| 0| 0| 0| ------------------------------------------- 

So you can see from the table the only bit they share together is the 8 bit.

Second example

$a = 36; $b = 103; echo $a & $b; // This would output the number 36. $a = 00100100 $b = 01100111 

The two shared bits are 32 and 4, which when added together return 36.

The "Or" operator: |

$a = 9; $b = 10; echo $a | $b; 

This would output the number 11. Why?

------------------------------------------- | 1 Byte ( 8 bits ) | ------------------------------------------- |Place Value | 128| 64| 32| 16| 8| 4| 2| 1| ------------------------------------------- | $a | 0| 0| 0| 0| 1| 0| 0| 1| ------------------------------------------- | $b | 0| 0| 0| 0| 1| 0| 1| 0| ------------------------------------------- | | | 0| 0| 0| 0| 1| 0| 1| 1| ------------------------------------------- 

You will notice that we have 3 bits set, in the 8, 2, and 1 columns. Add those up: 8+2+1=11.

Spaceship Operator <=> (Added in PHP 7)

Examples for <=> Spaceship operator (PHP 7, Source: PHP Manual):

Integers, Floats, Strings, Arrays & objects for Three-way comparison of variables.

// Integers echo 10 <=> 10; // 0 echo 10 <=> 20; // -1 echo 20 <=> 10; // 1 // Floats echo 1.5 <=> 1.5; // 0 echo 1.5 <=> 2.5; // -1 echo 2.5 <=> 1.5; // 1 // Strings echo "a" <=> "a"; // 0 echo "a" <=> "b"; // -1 echo "b" <=> "a"; // 1 echo "a" <=> "aa"; // -1 echo "zz" <=> "aa"; // 1 // Arrays echo [] <=> []; // 0 echo [1, 2, 3] <=> [1, 2, 3]; // 0 echo [1, 2, 3] <=> []; // 1 echo [1, 2, 3] <=> [1, 2, 1]; // 1 echo [1, 2, 3] <=> [1, 2, 4]; // -1 // Objects $a = (object) ["a" => "b"]; $b = (object) ["a" => "b"]; echo $a <=> $b; // 0 $a = (object) ["a" => "b"]; $b = (object) ["a" => "c"]; echo $a <=> $b; // -1 $a = (object) ["a" => "c"]; $b = (object) ["a" => "b"]; echo $a <=> $b; // 1 // only values are compared $a = (object) ["a" => "b"]; $b = (object) ["b" => "b"]; echo $a <=> $b; // 1 

_ Alias for gettext()

The underscore character '_' as in _() is an alias to gettext().

An overview of operators in PHP :


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.

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.

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

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.

{} Curly braces

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 

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Sajjad Hossain

I have five years of experience in web development sector. I love to do amazing projects and share my knowledge with all.

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