PHP Tutorials - Herong's Tutorial Examples - Version 4.20, by Dr. Herong Yang
Providing Default Values to Argument Variables
This section provides a tutorial example on how to provide default values to argument variables.
PHP also allows us to provide default values to argument variables using the following syntax on the function definition statement:
function function_name($arg_1, $arg_2, ... $arg_n=exp) { ... }
where argument variable, $arg_n, has been assigned with a default value, evaluated from the specified expression, "exp".
Assigning default values to argument variables has several simple rules:
To help us understand how use argument variable default values, I wrote this tutorial example:
<?php # ArgumentDefaultValues.php #- Copyright (c) 2003-2019, HerongYang.com, All Rights Reserved. # function hello($name="Herong") { print(" Hello " . $name . "!\n"); } print("\n Argument with a scalar default value:\n"); hello(); hello("World"); hello(NULL); function showList($list=array("Apple", "Orange")) { print(" List: " . $list[0] . ", " . $list[1] . "\n"); } print("\n Argument with an array default value:\n"); showList(); showList(array("Cat", "Dog")); # function showDate($object=new DateTime()) { # print(" Year: " . $object->format("Y")); # } ?>
If you run this sample script, you should get:
C:\herong> \php\php ArgumentDefaultValues.php Argument with a scalar default value: Hello Herong! Hello World! Hello ! Argument with an array default value: List: Apple, Orange List: Cat, Dog
If you open last 3 commented-out statements, you will get an execution error: "Parse error: syntax error, unexpected T_NEW in C:\herong\php\ArgumentDefaultValues.php on line 21",
Last update: 2019.
Table of Contents
Introduction and Installation of PHP 7.3
PHP Data Types and Data Literals
Variables, References, and Constants
Expressions, Operations and Type Conversions
Conditional Statements - "if" and "switch"
Loop Statements - "while", "for", and "do ... while"
►Function Declaration, Arguments, and Return Values
"function" Statements - Defining Functions
Passing Arguments to Functions
Example of Passing Arguments by Values
Using Pass-by-Value Arguments for References
Example of Passing Arguments by References
Variable-Length Argument Lists
►Providing Default Values to Argument Variables
Returning Values from Functions
Returning References from Functions
Introduction of Class and Object
Integrating PHP with Apache Web Server
Retrieving Information from HTTP Requests
Creating and Managing Sessions in PHP Scripts
Sending and Receiving Cookies in PHP Scripts
Controlling HTTP Response Header Lines in PHP Scripts
MySQL Server Connection and Access Functions
Functions to Manage Directories, Files and Images
SOAP Extension Function and Calling Web Services
SOAP Server Functions and Examples
Localization Overview of Web Applications
Using Non-ASCII Characters in HTML Documents
Using Non-ASCII Characters as PHP Script String Literals
Receiving Non-ASCII Characters from Input Forms
"mbstring" Extension and Non-ASCII Encoding Management
Managing Non-ASCII Character Strings with MySQL Servers