Functions

This chapter describes:

• How to define functions.
• How to pass references to and returning a reference from functions.

User Defined Functions

PHP supports user defined functions like in other languages, with some special features:

• By default, arguments are passed by value. But arguments can also be passed as references.
• Arguments can be assigned with default values.
• Functions can return values or references.
• Function names can also be string expressions. This is called variable functions.
• Functions can be defined inside another code block, or function.

Passing and Returning References

The following sample script shows how references can be passed to and returned from a function, FunctionTest.php:

<?php # FunctionTest.php
# Copyright (c) 2002 by Dr. Herong Yang, http://www.herongyang.com/
# 
   print "\nPassing arguments as references:\n";
   $x = "Apple";
   $y = "Orange";
   swap($x,$y); 
   print "   x = $x\n";
   print "   y = $y\n";
#
   print "\nReturning a reference:\n";
   $x = 10;
   $y = &ref($x);
   $x = 20;
   print "   y = $y\n";
#
function swap(&$a, &$b) {
   $c = $b;
   $b = $a; 
   $a = $c;
}
function &ref(&$a) {
   return $a;
}
?>

Here is the output of the program:

Passing arguments as references:
   x = Orange
   y = Apple

Returning a reference:
   y = 20

I am sure you know why we getting this output.