PHP Tutorials - Herong's Tutorial Examples - Version 4.20, by Dr. Herong Yang
Example of Passing Arguments by References
This section describes a second possible PWS Trojan infection that executed my.exe from C:\WINDOWS\Temp and another .exe file from C:\WINDOWS\system32. Both of them tried to install .sys files.
As we learned from the previous section, PHP supports pass-by-reference arguments if they are defined with a & prefix on the argument variables. If an argument is defined as an pass-by-reference argument, the calling operation can provide a variable, for this argument. The reference of that variable will be taken and assigned to this argument variable when function is called. For example, if we have "function f(&$var) {...}" defined, "f($arg)" is equivalent to "{$var=&$arg; ...}".
To see how passing arguments by references works, I wrote this tutorial example, PassByReference.php:
<?php # PassByReference.php #- Copyright (c) 2003-2019, HerongYang.com, All Rights Reserved. # function swap(&$left, &$right) { $temp = $left; $left = $right; $right = $temp; print(" Swapped in function: ".getString($left, $right)."\n"); } date_default_timezone_set("Europe/Paris"); # print("\n 1. Passing two literals:\n"); # print(" Before call: ". getString("Apple", "Orange") ."\n"); # swap("Apple", "Orange"); print("\n 2. Passing two variables:\n"); $x = "Dog"; $y = "Cat"; print(" Before call: ". getString($x, $y) ."\n"); swap($x, $y); print(" After call: ". getString($x, $y) ."\n"); print("\n 3. Passing two arrays:\n"); $x = array("Mon", "Tue"); $y = array("Jan", "Feb"); print(" Before call: ". getString($x, $y) ."\n"); swap($x, $y); print(" After call: ". getString($x, $y) ."\n"); print("\n 4. Passing two objects:\n"); $x = new DateTime("2005-01-01"); $y = new DateTime("2006-01-01"); print(" Before call: ". getString($x, $y) ."\n"); swap($x, $y); print(" After call: ". getString($x, $y) ."\n"); function getString($left, $right) { if (is_scalar($left)) { return "$left | $right"; } elseif (is_array($left)) { return "($left[0], $left[1]...) | ($right[0], $right[1]...)"; } elseif (is_object($left) && get_class($left)=="DateTime") { return $left->format("Y")." | ".$right->format("Y"); } else { return NULL; } } ?>
If you run this sample script, you should get:
C:\herong> \php\php PassByReference.php 2. Passing two variables: Before call: Dog | Cat Swapped in function: Cat | Dog After call: Cat | Dog 3. Passing two arrays: Before call: (Mon, Tue...) | (Jan, Feb...) Swapped in function: (Jan, Feb...) | (Mon, Tue...) After call: (Jan, Feb...) | (Mon, Tue...) 4. Passing two objects: Before call: 2005 | 2006 Swapped in function: 2006 | 2005 After call: 2006 | 2005
The output confirms that:
Exercise: Try to test pass-by-reference arguments with:
swap("Apple", "Orange"); swap(array("Mon", "Tue"), array("Jan", "Feb")); swap(new DateTime("2015-01-01"), new DateTime("2016-01-01")); swap(&$a, &$b);
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