Passing by Reference

You can pass variable to function by reference, so that function could modify its arguments. The syntax is as follows:

<?php
function foo (&$var)
{
    
$var++;
}

$a=5;
foo ($a);
// $a is 6 here
?>

Note that there's no reference sign on function call - only on function definition. Function definition alone is enough to correctly pass the argument by reference.

Following things can be passed by reference:

Any other expression should not be passed by reference, as the result is undefined. For example, the following examples of passing by reference are invalid:

<?php
function bar() // Note the missing &
{
    
$a = 5;
    return
$a;
}
foo(bar());

foo($a = 5); // Expression, not variable
foo(5); // Constant, not variable
?>

These requirements are for PHP 4.0.4 and later.


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