The role of include_once in php

The role of include_once in PHP: include external files only once to avoid repeated execution. Load the function library and expand the script function. Improve performance and avoid code duplication.

The role of include_once in PHP

include_once is an important precompilation directive in PHP, which is responsible for including external files or scripts into the current in the script. Its function is as follows:

Include only once:
Compared with include, the main feature of include_once is that it ensures that external files will only be included once. Even if the file is included repeatedly in the current script, it will not be executed again.

Avoid duplicating code:
By using include_once, you can avoid repeatedly including the same external files in your script. This helps reduce code duplication and improve performance.

Load function library:
include_once is usually used to load external files containing function and class definitions, thus extending the available functionality of the current script.

Example:

include_once "functions.php"; // 加载包含函数定义的文件

How it works:
include_once will check whether the external file exists, and if not, include it into the current in the script. If the file already exists, it is checked to see if it has already been included. If it's already included, it won't be included again, thus avoiding code duplication.

Advantages:

• Avoid duplication of code
• Improve performance
• Expand script functionality

Note:
When using include_once, you need to pay attention to whether the file path is correct, otherwise it may cause script errors.

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