Briefly talk about include, include_once, require and require_once statements in PHP_php skills

1.include statement

Use the include statement to tell PHP to extract a specific file and load its entire contents

<&#63;php
inlude "fileinfo.php";

//此处添加其他代码
&#63;>

2.include_once statement

Every time you use the include statement, it will re-import the requested file, even if the file has already been imported. For example, assume that the fileinfo.php file contains many functions. We use the include statement to import it into an existing file. Then we import a file that contains fileinfo.php. Through nesting, we have imported the fileinfo.php file. twice, this will generate an error because we are trying to define a variable or function with the same name multiple times. In order to avoid this happening, we use the include_once statement instead of the include statement

<&#63;php
include_once "fileinfo.php";

//此处添加其他代码
&#63;>

At this point, if another include or include_once statement is encountered in the same file, PHP will check whether it has already been imported, and if so, ignore it.

3.require and require_once statements

A potential problem with using include and include_once statements is that PHP will only try to import the file that is requested to be imported. Even if the file is not found, the program will still execute.
When we absolutely need to import a file, we use the require statement. The reason for using the require_once statement is the same, so I won’t go into details here.

<&#63;php
require_once "fileinfo.php";

//此处添加其他代码
&#63;>

In general, we should stick to require_once statements.