What is the concept contained in the PHP file

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I. the concepts contained in the document

In a PHP script, to include another file (PHP) to collaborate on something.

II. The role of the document

Or use the contents of the included file to achieve code sharing (reuse): include (request) up: include other files before the current script uses some code

Or you can have something for other files to share (reuse): include (give) downwards: when you have something, you need another script to display (include other files after your own code is written)

The biggest role: division of labor and cooperation, each script does different things, so you can use a collaborative approach to let multiple scripts work together to accomplish one thing.

III. Four forms contained in the document

Include: include fil

Include_once: the system will automatically determine whether a file has been included during the inclusion process (a file is included at most once)

Require: same as include

Require_once: same as include_once

(1) include up-include the file first, and then use the contents of the file

Included file code

File include-included file