Returning values

Values are returned by using the optional return statement. Any type may be returned, including lists and objects.

 function my_sqrt ($num) {
     return $num * $num;
 }
 echo my_sqrt (4);   // outputs '16'.
       

Multiple values may not be returned, but the same effect can be achieved by returning a list:

 function foo() {
    return array (0, 1, 2);
 }
 list ($zero, $one, $two) = foo();
       

Arguments

Information may be passed to functions via the argument list, which is a comma-delimited list of variables and/or constants.

PHP supports passing arguments by value (the default), passing by reference, and default argument values. Variable-length argument lists are not supported, but a similar effect may be achieved by passing arrays.

 function takes_array($input) {
     echo "$input[0] + $input[1] = ", $input[0]+$input[1];
 }
       

Passing by reference

By default, function arguments are passed by value. If you wish to allow a function to modify its arguments, you may pass them by reference.

If you wish a function's argument to always be passed by reference, you can prepend an ampersand (&) to the argument name in the function definition:

 function foo( &$bar ) {
     $bar .= 'and something extra.';
 }
 $str = 'This is a string, ';
 foo ($str);
 echo $str;    // outputs 'This is a string, and something extra.'
        

If you wish to pass a variable by reference to a function which does not do this by default, you may prepend an ampersand to the argument name in the function call:

 function foo ($bar) {
     $bar .= ' and something extra.';
 }
 $str = 'This is a string, ';
 foo ($str);
 echo $str;    // outputs 'This is a string, '
 foo (&$str);
 echo $str;    // outputs 'This is a string, and something extra.'
        

Default values

A function may define C++-style default values for scalar arguments as follows:

 function makecoffee ($type = "cappucino") {
     echo "Making a cup of $type.\n";
 }
 echo makecoffee ();
 echo makecoffee ("espresso");
        

The output from the above snippet is:

 Making a cup of cappucino.
 Making a cup of espresso.
       

The default value must be a constant expression, not (for example) a variable or class member.

Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected. Consider the following code snippet:

 function makeyogurt ($type = "acidophilus", $flavour) {
     return "Making a bowl of $type $flavour.\n";
 }
 
 echo makeyogurt ("raspberry");   // won't work as expected
        

The output of the above example is:

 Warning: Missing argument 2 in call to makeyogurt() in 
 /usr/local/etc/httpd/htdocs/php3test/functest.html on line 41
 Making a bowl of raspberry .
       

Now, compare the above with this:

 function makeyogurt ($flavour, $type = "acidophilus") {
     return "Making a bowl of $type $flavour.\n";
 }
 
 echo makeyogurt ("raspberry");   // works as expected
        

The output of this example is:

 Making a bowl of acidophilus raspberry.