The difference between include() and require() and include_once() and require_once() in PHP_PHP Tutorial

The difference between include() and require() and include_once() and require_once() in php

All four have the meaning of including files, but include() and include_once() will continue to execute the program when an error occurs in the included file, while require() and require_once() will not. In addition, include_once() and require_once() only Included once, excess will not be included. example:

$a=5;

//include('./test.php');//The code in test.php is $a =3;

//require('./test.php');

//echo $a;//The result is 8;

//When including the non-existent file test1.php

//include('./test1.php');//The result prompts warning and outputs 5;

//require('./test1.php');//The result prompts a fatal error and stops the program from executing

//echo $a;

include_once('./test.php');

include_once('./test.php');

include_once('./test.php');

include_once('./test.php');

echo $a;

//The result output is 8, because if there are multiple include_once() or require_once(), only the first one will be executed. If there are multiple include() or require(), they will all be executed

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