About loading classes in PHP

Object-oriented is an important idea, and classes are also important concepts in object-oriented, but class loading is the key to using classes.

There are two ways to access classes:

• Access through instantiated objects

• Access to class members

The prerequisite for access is that there is a class in the memory, so the class needs to be loaded into the memory in advance.

1. Manual loading

//类文件 Salary.php 

应用文件：useSalary.php Student(); ?>

2. Automatic loading

• The automatic loading mechanism used before PHP7: Use the __autoload() function provided by the system. Then when the system needs to use the class and it does not exist in the memory, the system will automatically call the __autoload() function to load the class file. .

//若在不同路径下 

• After PHP7, it is not recommended to use the __autoload() function, but to use a registration mechanism to customize the user The function is placed inside the system and uses spl_autoload_register (defined function).

//可以定义多个方法 

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