Is there a PHP function for swapping the values of two variables?

Question

Say for instance I have ...

$var1 = \"ABC\"
$var2 = 123

and under certain conditions I want to sw

Answer 1

There's no function I know of, but there is a one-liner courtesy of Pete Graham:

list($a,$b) = array($b,$a);

not sure whether I like this from a maintenance perspective, though, as it's not really intuitive to understand.

Also, as @Paul Dixon points out, it is not very efficient, and is costlier than using a temporary variable. Possibly of note in a very big loop.

However, a situation where this is necessary smells a bit wrong to me, anyway. If you want to discuss it: What do you need this for?

Answer 2

Yes I know there are lots of solutions available, but here is another one. You can use parse_str() function too. Reference W3Schools PHP parse_str() function.

<?php
    $a = 10;
    $b = 'String';

    echo '$a is '.$a;
    echo '....';
    echo '$b is '.$b;

    parse_str("a=$b&b=$a");

    echo '....After Using Parse Str....';

    echo '$a is '.$a;
    echo '....';
    echo '$b is '.$b;

?>

DEMO

Answer 3

Thanks for the help. I've made this into a PHP function swap()

function swap(&$var1, &$var2) {
    $tmp = $var1;
    $var1 = $var2;
    $var2 = $tmp;
}

Code example can be found at:

http://liljosh.com/swap-php-variables/

Answer 4

Yes, try this:

// Test variables
$a = "content a";
$b = "content b";

// Swap $a and $b
list($a, $b) = array($b, $a);

This reminds me of python, where syntax like this is perfectly valid:

a, b = b, a

It's a shame you can't just do the above in PHP...

Answer 5

another simple method

$a=122;
$b=343;

extract(array('a'=>$b,'b'=>$a));

echo '$a='.$a.PHP_EOL;
echo '$b='.$b;

Answer 6

3 options:

$x ^= $y ^= $x ^= $y; //bitwise operators

or:

list($x,$y) = array($y,$x);

or:

$tmp=$x; $x=$y; $y=$tmp;

I think that the first option is the fastest and needs lesser memory, but it doesn’t works well with all types of variables. (example: works well only for strings with the same length)
Anyway, this method is much better than the arithmetic method, from any angle.
(Arithmetic: {$a=($a+$b)-$a; $b=($a+$b)-$b;} problem of MaxInt, and more...)

Functions for example:

function swap(&$x,&$y) { $x ^= $y ^= $x ^= $y; }
function swap(&$x,&$y) { list($x,$y) = array($y,$x); }
function swap(&$x,&$y) { $tmp=$x; $x=$y; $y=$tmp; }

//usage:
swap($x,$y);