What is the difference between include and require in PHP? What is the difference between Include_once?

The previous article introduced to you "What are the commonly used system functions for files in PHP? What is the principle of loading files? 》, this article continues to introduce to you what is the difference between include and require in PHP? What is the difference between Include_once? It has certain reference value. Friends in need can refer to it. I hope it will be helpful to everyone.

●The difference between Include and require.

First understand the difference between Include and include_once:

Include system will encounter it once and execute it once; if the same file is loaded multiple times , then the system will execute it multiple times;

Include_once:

If the system encounters it multiple times, it will only execute it once

Specifically, we use the code as Example:

Create two files named include1 and include2 respectively; the code is as follows:

include1:

<?php
//被包含的文件
//定义数据
$a = 1;
define(&#39;PI&#39;,3.14);
?>

include2:

<?php
//包含文件:使用数据
//包含文件
include &#39;include1.php&#39;; //包含当前文件include2. php所在文件夹下的include1. php
echo $a,PI;
//再次加重
include &#39;include1.php&#39;;
?>

Code demonstration results As follows:

When we comment out include 'include1.php'; based on the original code, then we add

include_once 'include1.php'; The running result will show that notices and errors are no longer reported, but we need to pay attention to the fact that the same constant may have repeated definitions, that is, if the inclusion is successful, it will be repeated. Defined. At this time, there is no error in the result of our second run, because the system finds that we have defined it once in include1. We can know that the system will automatically query, so we also know that Include_once:

The system encountered Multiple times, it will only be executed once

, this is the most obvious difference between Include and include_once

The difference between Require and include: The essence is that they both include files, the only difference is that include When the file is not found, the error form is different.

Specifically, let’s take the code as an example:

We first define a file randomly, and the results show two errors. First, it says that the system cannot open the file we defined. Second, the system cannot find it. to the file, but the system reports a warning, which does not affect our execution. When we put the code normally below the code, we will find that it will be parsed normally.

<?php
//require和include的区别
//include包含文件
include &#39;b.php&#39;;
?>

The code demonstration results are as follows:

<?php
//require和include的区别
//include包含文件
include &#39;a.php&#39;;
echo &#39;我喜欢你&#39;;
?>

The code demonstration results are as follows:

As can be seen from the above, although we will report an error above, it will not affect our execution results. ;

The error level of Include is relatively mild: it will not prevent code execution.

Requires higher requirements: if it contains an error code, it will not be executed (the code after require)

Specifically, we use the code as Example:

<?php
//require和include的区别
//include包含文件
//include &#39;a.php&#39;;
//requre 包含文件
require &#39;b.php&#39;;
echo &#39;我喜欢你&#39;;
?>

The code demonstration result is as follows:

The one difference from the code we run above is that require will report a fatal error: not found Corresponding file, and the code we entered will no longer be executed

Recommended learning: "PHP Video Tutorial"

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