search
HomeBackend DevelopmentPHP TutorialDetailed explanation of __autoload() magic method in PHP

This article will introduce you to the __autoload() magic method in PHP. I hope it will be helpful to friends in need!

__autoload(), trying to load an undefined class

Function:

You can enable it by defining this function Automatic loading of classes.

Before the magic function __autoload() method appeared, if you wanted to instantiate 100 objects in a program file, then you must use include or require to include 100 class files, or you must include these 100 Each class is defined in the same class file - I believe this file will be very large, and then you will be in pain.

But with the __autoload() method, you don’t have to worry about this in the future. This class will automatically load the specified file before you instantiate the object.

Let’s take a look through examples:

Let’s look at the previous methods first:

/** 
 * 文件non_autoload.php 
 */ 
   
require_once('project/class/A.php');  
require_once('project/class/B.php');  
require_once('project/class/C.php');  
   
if (条件A) {  
    $a = new A();  
    $b = new B();  
    $c = new C();  
    // … 业务逻辑  
} else if (条件B) {  
    $a = newA();  
    $b = new B();  
    // … 业务逻辑  
}

Do you see it? Not 100, just 3 seems a bit annoying. And there will be a problem: if the script executes the "Condition B" branch, the file C.php actually does not need to be included. Because any included file, whether used or not, will be compiled by the PHP engine.

If it is not used but compiled, this can be regarded as a waste of resources. Furthermore, if C.php contains D.php, D.php contains E.php. And in most cases, the "Conditional B" branch is executed, which will waste some resources to compile three "useless" files C.php, D.php, and E.php.

So what if you use the __autoload() method?

/** 
 * 文件autoload_demo.php 
 */ 
function  __autoload($className) {  
    $filePath = “project/class/{$className}.php”;  
    if (is_readable($filePath)) {  
        require($filePath);  
    }  
}  
   
if (条件A) {  
    $a = new A();  
    $b = new B();  
    $c = new C();  
    // … 业务逻辑  
} else if (条件B) {  
    $a = newA();  
    $b = new B();  
    // … 业务逻辑  
}

ok, no matter how efficient it is, at least the interface looks much more comfortable, without too many redundant codes.

Let’s take a look at the efficiency here. Let’s analyze it:

When the php engine uses class A for the first time but cannot find it, it will automatically call the __autoload method and add the class The name "A" is passed in as a parameter. Therefore, what we need to do in __autoload() is to find the corresponding file based on the class name and include it. If our method cannot find it, then the PHP engine will report an error.

Note:

You can only use require here, because once it is included, when the php engine encounters class A again, it will not call __autoload, but Using class A directly in memory will not result in multiple inclusions.

Extension:

In fact, with the development of PHP today, `spl_autoload_register` - registering a given function as the implementation of __autoload has been implemented, but this is not included in this article. Within the explanation, if you are interested, you can read the manual on your own.

Recommended PHP practical tutorialhttps://www.php.cn/k.html

The above is the detailed content of Detailed explanation of __autoload() magic method in PHP. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Explain the concept of a PHP session in simple terms.Explain the concept of a PHP session in simple terms.Apr 26, 2025 am 12:09 AM

PHPsessionstrackuserdataacrossmultiplepagerequestsusingauniqueIDstoredinacookie.Here'showtomanagethemeffectively:1)Startasessionwithsession_start()andstoredatain$_SESSION.2)RegeneratethesessionIDafterloginwithsession_regenerate_id(true)topreventsessi

How do you loop through all the values stored in a PHP session?How do you loop through all the values stored in a PHP session?Apr 26, 2025 am 12:06 AM

In PHP, iterating through session data can be achieved through the following steps: 1. Start the session using session_start(). 2. Iterate through foreach loop through all key-value pairs in the $_SESSION array. 3. When processing complex data structures, use is_array() or is_object() functions and use print_r() to output detailed information. 4. When optimizing traversal, paging can be used to avoid processing large amounts of data at one time. This will help you manage and use PHP session data more efficiently in your actual project.

Explain how to use sessions for user authentication.Explain how to use sessions for user authentication.Apr 26, 2025 am 12:04 AM

The session realizes user authentication through the server-side state management mechanism. 1) Session creation and generation of unique IDs, 2) IDs are passed through cookies, 3) Server stores and accesses session data through IDs, 4) User authentication and status management are realized, improving application security and user experience.

Give an example of how to store a user's name in a PHP session.Give an example of how to store a user's name in a PHP session.Apr 26, 2025 am 12:03 AM

Tostoreauser'snameinaPHPsession,startthesessionwithsession_start(),thenassignthenameto$_SESSION['username'].1)Usesession_start()toinitializethesession.2)Assigntheuser'snameto$_SESSION['username'].Thisallowsyoutoaccessthenameacrossmultiplepages,enhanc

What are some common problems that can cause PHP sessions to fail?What are some common problems that can cause PHP sessions to fail?Apr 25, 2025 am 12:16 AM

Reasons for PHPSession failure include configuration errors, cookie issues, and session expiration. 1. Configuration error: Check and set the correct session.save_path. 2.Cookie problem: Make sure the cookie is set correctly. 3.Session expires: Adjust session.gc_maxlifetime value to extend session time.

How do you debug session-related issues in PHP?How do you debug session-related issues in PHP?Apr 25, 2025 am 12:12 AM

Methods to debug session problems in PHP include: 1. Check whether the session is started correctly; 2. Verify the delivery of the session ID; 3. Check the storage and reading of session data; 4. Check the server configuration. By outputting session ID and data, viewing session file content, etc., you can effectively diagnose and solve session-related problems.

What happens if session_start() is called multiple times?What happens if session_start() is called multiple times?Apr 25, 2025 am 12:06 AM

Multiple calls to session_start() will result in warning messages and possible data overwrites. 1) PHP will issue a warning, prompting that the session has been started. 2) It may cause unexpected overwriting of session data. 3) Use session_status() to check the session status to avoid repeated calls.

How do you configure the session lifetime in PHP?How do you configure the session lifetime in PHP?Apr 25, 2025 am 12:05 AM

Configuring the session lifecycle in PHP can be achieved by setting session.gc_maxlifetime and session.cookie_lifetime. 1) session.gc_maxlifetime controls the survival time of server-side session data, 2) session.cookie_lifetime controls the life cycle of client cookies. When set to 0, the cookie expires when the browser is closed.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function

Atom editor mac version download

Atom editor mac version download

The most popular open source editor

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.