How to use php require_once

In PHP, the require_once statement is used to reference or include an external PHP file, the syntax is "require_once(filename)" or "require_once 'filename'"; if the file specified by the statement has already been included, then Will not be included again.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

php require_once statement

require_once: Its function is the same as require, both refer to or include an external php file

Principle: When the php file containing require_once is executed, it is specified by require_once All external files will be included, form a new php file with other code, and start executing

Syntax: "require_once(filename)" or "require_once 'filename'"

Note:

1. When the external included file has an error, it will also run incorrectly and terminate the operation.

2. In the application The require_once statement will first check whether the file to be included has been included elsewhere in the program. If so, the file will not be included again.

Example:

a.php

<?php 
echo "Hello";
?>

b.php

<?php
    require &#39;a.php&#39;;
    require_once &#39;a.php&#39;;
?>

Run b.php The result is:

Hello

Note: The result only outputs a Hello, indicating that the code in a.php is only referenced once.

Recommended learning: "PHP Video Tutorial"

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