Passing by Reference

You can pass a variable by reference to a function so the function can modify the variable. The syntax is as follows:

Note: There is no reference sign on a function call - only on function definitions. Function definitions alone are enough to correctly pass the argument by reference. As of PHP 5.3.0, 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:

• Variables, i.e. foo($a)
• New statements, i.e. foo(new foobar())

• References returned from functions, i.e.:

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

These requirements are for PHP 4.0.4 and later.