ZEND PHP 5 Certification STUDY GUIDE

42 ” Functions
Variable-length Argument Lists
A common mistake when declaring a function is to write the following:
function f ($optional = "null", $required)
{
}
This does not cause any errors to be emitted, but it also makes no sense whatsoever—because
you will never be able to omit the first parameter ($optional) if you
want to specify the second, and you can’t omit the second because PHP will emit a
warning.
In this case, what you really want is variable-length argument lists—that is, the
ability to create a function that accepts a variable number of arguments, depending
on the circumstance. A typical example of this behaviour is exhibited by the printf()
family of functions.
PHP provides three built-in functions to handle variable-length argument lists:
func_num_args(), func_get_arg() and func_get_args(). Here’s an example of how
they’re used:
function hello()
{
if (func_num_args() > 0) {
$arg = func_get_arg(0); // The first argument is at position 0
echo "Hello $arg";
} else {
echo "Hello World";
}
}
hello("Reader"); // Displays "Hello Reader"
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)
hello(); // Displays "Hello World"
You can use variable-length argument lists even if you do specify arguments in the
function header. However, this won’t affect the way the variable-length argument list
functions behave—for example, func_num_args() will still return the total number of
arguments passed to your function, both declared and anonymous.