Usage of require_once in php

require_once function is used in PHP to include files to ensure that the file is only included once to avoid repeated inclusion errors. Syntax: require_once(string $filename) Parameters: $filename, the file path to be included. Function: Include the specified file into the current script. If the file is already included, it will no longer be included. Difference: Similar to include_once, but if the file is not found, require_once generates a fatal error and interrupts execution, while include_once generates a warning.

Usage of require_once in PHP

require_once is a function in PHP used to include files, which ensures A file is only included once to avoid errors caused by including files twice.

Syntax

require_once(string $filename);

Parameters

Parameters	Description
filename	The path to the file to include.

Function

require_once function includes the specified file into the current script. The specified filename is included if it is not already included. If it is already included, no further inclusion is performed.

Differences from include_once

require_once and include_once functions have similar functions, but they differ in error handling:

• If filename If not found, require_once will cause a fatal error and interrupt script execution.
• If filename is not found, include_once will generate a warning but will not interrupt script execution.

Note:

• Always use absolute paths to avoid accidentally including the wrong file.
• Use require_once with caution, especially when including larger or complex files, as it may affect the performance of your script.

Example

The following is an example of using require_once to include files:

<?php
require_once('header.php'); // 包含头部文件

echo "页面内容"; // 执行页面内容

require_once('footer.php'); // 包含尾部文件
?>

In this example, the header and tail files are only will be included once, even if they are called multiple times in the script.

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