You can pass a variable by reference to a function so the function can modify the variable. The syntax is as follows:
<?php
function foo(&$var)
{
$var++;
}
$a=5;
foo($a);
// $a is 6 here
?>
Note that there's no reference sign on a function call - only on function definitions. Function definitions alone are enough to correctly pass the argument by reference. In recent versions of PHP you will get a warning saying that "call-time pass-by-reference" is deprecated when you use & in foo(&$a);.
The following things can be passed by reference:
References returned from functions, i.e.:
<?php
function &bar()
{
$a = 5;
return $a;
}
foo(bar());
?>
See more about returning by reference.
No other expressions should 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 $a;
}
foo(bar()); // Produces fatal error since PHP 5.0.5
foo($a = 5); // Expression, not variable
foo(5); // Produces fatal error
?>
These requirements are for PHP 4.0.4 and later.