Zend PHP 7 Certification – Functions – Arguments

15th November 2017

This post covers the Arguments section of the Functions chapter when studying for the Zend PHP 7 Certification.

Information may be passed to functions via the argument list, which is a comma-delimited list of expressions.

<?php
function somefunction($arg1, $arg2, $arg3) {
    // Do something
}

Arguments are evaluated from left to right. This means that the below example would output abc.

<?php
function myFunction($x, $x = 1, $x = 2, $x = "abc") {
    return $x;
}

echo myFunction(0); // abc

The func_num_args() function returns the number of arguments that are passed to the function.

<?php
function foo() {
    $numargs = func_num_args();
    echo "Number of arguments: $numargs\n";
}

foo(1, 2, 3, 'test'); // Outputs: Number of arguments: 4

This function can be used in conjunction with func_get_arg() and func_get_args()

func_get_arg() will get the specified argument from a user-defined function’s argument list.

mixed func_get_arg ( int $arg_num )

Where $arg_num is the argument offset. Function arguments are counted starting from zero.

<?php
function foo() {
    echo "Second argument is: " . func_get_arg(1);
}

foo(1, 2, 3); // Outputs: Second argument is: 2

The func_get_args() will return an array comprising a function’s argument list.

<?php
function foo() {
    $arg_list = func_get_args();
    print_r($arg_list);
}

foo(1, 'abc', array()); // Outputs: Array ( [0] => 1 [1] => abc [2] => Array ( ) )

Note that passing by arguments by reference will change the output of func_get_args() if the argument is altered within the function.

Passing by value:

<?php
function foo($x, $y, $z)
{
    $y = 'def';
    $arg_list = func_get_args();
    print_r($arg_list);
}

$str = 'abc';
foo(1, $str, array()); // Outputs: Array ( [0] => 1 [1] => abc [2] => Array ( ) )

Passing $y by reference:

<?php
function foo($x, &$y, $z) {
    $y = 'def';
    $arg_list = func_get_args();
    print_r($arg_list);
}

$str = 'abc';
foo(1, $str, array()); // Outputs: Array ( [0] => 1 [1] => def [2] => Array ( ) )

By default, function arguments are passed by value (so that if the value of the argument within the function is changed, it does not get changed outside of the function).

To allow a function to modify its arguments, they must be passed by reference.

To have an argument to a function always passed by reference, prepend an ampersand, &, to the argument name in the function definition.

Passed by value:

<?php
function add_some_extra($string) {
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // Outputs: This is a string, 

Passed by reference:

<?php
function add_some_extra(&$string) {
    $string .= 'and something extra.';
}
$str = 'This is a string, ';
add_some_extra($str);
echo $str;    // Outputs: This is a string, and something extra.

Type declarations allow functions to require that parameters are of a certain type at call time.

<?php
function test(boolean $param) {}

test(true);

If the given value is of the incorrect type, then a TypeError exception is thrown. More on type declarations can be found in the Type Declarations section.

View the other sections:

• Syntax
• Variables
• References
• Returns
• Type Declarations
• Variable Scope
• Anonymous Functions

Note: This article is based on PHP version 7.1.