PHP advanced user defined functions. Free online PHP and MySQL Web Database Programming Tutorial...

Generally PHP functions are passed arguments by value, this is the default behavior in PHP. PHP also support passing function arguments by reference, and default argument values. If we need to pass an argument to a fuction by reference we must prepend an ampersand (&) to the argument name in the function definition. Consider the following example:

<?php
function add_extra(&$string) {
$string .= 'and this is extra string.';
}
$str = 'This is a string, ';
add_extra($str);
echo $str; // outputs 'This is a string, and this is extra string.
?>
A function in PHP can't return multiple values, but similar result can be obtained by returning an array as shown below:

<?php
function numbers() {
return array (0, 1, 2, 3);
}
?>
To return a reference from a function, we have to use the reference operator & in both the function declaration and when assigning the returned value to a variable as shown in the following example:

<?php
function &returns_ref() {
return $someref;
}
$newref =& returns_ref();
?>

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