Detailed explanation of __autoload() method in php_PHP tutorial

Before the magic function __autoload() method appeared in PHP, if you wanted to instantiate 100 objects in a program file, then you had to include 100 class files using include or require, or you defined these 100 classes in the same program file. In a class file - I believe this file will be very large.

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

Let’s take a look at the specific usage through an example, and explain later what you should pay attention to when using the PHP magic function __autoload.

After defining two classes for testing, we To write a PHP running program file containing the __autoload() method as follows:

The code is as follows

代码如下	复制代码
//定义一个类ClassA，文件名为ClassA.php class ClassA{  public  function __construct(){   echo "ClassA load success!";  } }  //定义一个类ClassB，文件名为ClassB.php，ClassB继承ClassA class ClassB extends ClassA {  public function __construct(){   //parent::__construct();   echo "ClassB load success!";  } }

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代码如下	复制代码
function __autoload($classname){  $classpath="./".$classname.'.php';  if(file_exists($classpath)){   require_once($classpath);  }  else{   echo 'class file'.$classpath.'not found!';  } }   $newobj = new ClassA(); $newobj = new ClassB();

//Define a class ClassA, the file name is ClassA.php

class ClassA{
public function __construct(){

echo "ClassA load success!";

}
}

代码如下	复制代码
Fatal error: Class ‘Classd’ not found in ……ClassB.php on line 2，

//Define a class ClassB, the file name is ClassB.php, ClassB inherits ClassA

class ClassB extends ClassA {

public function __construct(){

//parent ::__construct();

echo "ClassB load success!";

}
}

The code is as follows

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function __autoload($classname){ $classpath="./".$classname.'.php'; if(file_exists($classpath)){ require_once($classpath); } else{ echo 'class file'.$classpath.'not found!'; }} $newobj = new ClassA();$newobj = new ClassB(); The operation of this file is There is no problem at all, which shows how easy to use autoload is, haha... But I have to remind you that you must pay attention to several aspects. 1. If the class has an inheritance relationship (for example: ClassB extends ClassA), and ClassA is not in the directory where ClassB is located When you use the __autoload magic function to instantiate ClassB, you will receive a fatal error: Solution: Put all classes with extends relationship in the same file directory, or manually include the inherited class in the file when instantiating an inherited class; 2 , Another thing to note is that the class name and the file name of the class must be consistent to make it easier to use the magic function __autoload; Other things to note: 3. Run PHP in CLI mode This method is invalid for scripts; 4. If your class name is related to user input - or depends on user input, be sure to check the input file name, for example: .././ like this The file name is very dangerous. http://www.bkjia.com/PHPjc/444710.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/444710.htmlTechArticlePHP Before the magic function __autoload() method appeared, if you wanted to instantiate 100 in a program file Object, then you must use include or require to include 100 class files, or...