What is the difference between include() function and require() function in php?

The content of this article is about the difference between the include() function and the require() function in PHP. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

There is too much information on the Internet about the difference between include and require in PHP. In fact, nothing said can stand verification. I randomly found a screenshot as follows:

and I still swear by the explanation: include() is a conditional inclusion function, while require() is an unconditionally included function.

But this happened a long time ago. There are indeed differences between require and include in current PHP. The author tested version 5.3 or above. The test results are as follows:

I found that these two structures are except in Performance is exactly the same except how containment failures are handled.

1. In terms of performance

The test found that there is not much difference in performance between require and include. I feel that this aspect does not need to be considered (maybe I did not test enough samples)

<pre name="code" class="php">$startTime=time();
$startMemoryUsed=memory_get_usage();  
require "a1.inc";
$endMemoryUsed=memory_get_usage();
$endTime=time();
$usedMemory=($endMemoryUsed-$startMemoryUsed)/1024; 
print_r($usedMemory);//1.6171875
echo &#39;</br>&#39;;
print_r($endTime-$startTime);
/*$startTime=time();
$startMemoryUsed=memory_get_usage();  
include "a1.inc";
$endMemoryUsed=memory_get_usage();  
$endTime=time();
$usedMemory=($endMemoryUsed-$startMemoryUsed)/1024; 
print_r($usedMemory);//1.6171875
print_r($endTime-$startTime);*/

2. In terms of include error handling

When inclusion fails, include() generates a warning and continues execution, while require() causes a fatal error. In other words, use require() if you want to stop processing the page when a missing file is encountered, otherwise use include().

include "a9.inc";//<span style="font-family: Arial, Helvetica, sans-serif;">a9.inc不存在会产生一个警告</span>
require "a10.inc";//a10.inc不存在会产生一个致命错误

Supplement: include, require include scope

File a2.inc

$name="lidquan";
class Teacher{
    public function show(){
        echo &#39;my job is teacher</br>&#39;;
    }
}
function showName(){
    echo &#39;a2.inc 里面的方法&#39;;
}

The screenshot of the file index.php

function a(){
    require "a2.inc";
    $teacher =new Teacher();
    $teacher->show();
}
 
a();//正常调用
 
showName();//正常调用
 
var_dump($name);//提示$name没有定义

is as follows:

The summary of scope issues after including the file is as follows:

1. All in After being included, the functions and classes defined in the included file have global scope in the included file

2. The scope of the variables of the included file changes with the change of the included position. Variety. For example, if it is included in a function, the variables of the included file are local variables

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