Last updated: Fri, 01 Jun 2007

Assignment Operators

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

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


<?php



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



?>

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


<?php



$a = 3;

$a += 5; // sets $a to 8, as if we had said: $a = $a + 5;

$b = "Hello ";

$b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";



?>

Note that the assignment copies the original variable to the new one (assignment by value), so changes to one will not affect the other. This may also have relevance if you need to copy something like a large array inside a tight loop. 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. As of PHP 5, objects are assigned by reference unless explicitly told otherwise with the new clone keyword.

add a note User Contributed Notes
Assignment Operators

adam at gmail dot com
25-Aug-2006 05:38


or you could use the xor-assignment operator..

$a ^= $b;

$b ^= $a;

$a ^= $b;

bradlis7 at bradlis7 dot com
15-Aug-2005 03:13


Note whenever you do this



<?php

$a .= $b .= "bla bla";

?>



it comes out to be the same as the following:



<?php

$a .= $b."bla bla";

$b .= "bla bla";

?>



So $a actually becomes $a and the final $b string. I'm sure it's the same with numerical assignments (+=, *=...).

straz at mac dot nospam dot com
21-Feb-2004 06:18


This page really ought to have table of assignment operators,

namely,



See the Arithmetic Operators page (http://www.php.net/manual/en/language.operators.arithmetic.php)

Assignment    Same as:

$a += $b     $a = $a + $b    Addition

$a -= $b     $a = $a - $b     Subtraction

$a *= $b     $a = $a * $b     Multiplication

$a /= $b     $a = $a / $b    Division

$a %= $b     $a = $a % $b    Modulus



See the String Operators page(http://www.php.net/manual/en/language.operators.string.php)

$a .= $b     $a = $a . $b       Concatenate



See the Bitwise Operators page (http://www.php.net/manual/en/language.operators.bitwise.php)

$a &= $b     $a = $a & $b     Bitwise And

$a |= $b     $a = $a | $b      Bitwise Or

$a ^= $b     $a = $a ^ $b       Bitwise Xor

$a <<= $b     $a = $a << $b     Left shift

$a >>= $b     $a = $a >> $b      Right shift

add a note

Bitwise Operators

Arithmetic Operators

Last updated: Fri, 01 Jun 2007