The use of PHP require_once and the difference from require

difference:

Require_once will only load the same file once, require will load multiple times.

I believe that the same as my small white or some doubts it. So we assume: if 456.php introduced 123.php, now file test_require.php introduced "456.php" and "123.php". If the Require method is used, then in test_require.php, 123.php is introduced 2 times, and 123.php is introduced once using the Require_once method. Then let's do the experiment!

First, Require method

The contents of 123.php are as follows:

 
The 456.php content is as follows:
 
   Require ("123.php");  echo "456\n";
The contents of test_require.php are as follows:
  Run test_require.php to get the result as follows:

Second, require_once method
123.php content does not change. 456.php and test_require.php Change the Require_once method. The contents are as follows:
//456.php!--? phprequire_once "123.php"; echo "456\n";//test_require.php
     Run test_require.php with the following result: 
 
 
 
 
  third, mixed error  
 
  If you use the Require method in 456.php, the Require_ Once method, then the require_once will fail. Three file codes are as follows:  
 
 
 
//123.php!--? Phpecho "123\n";//456.php
       The result of the operation is as follows:  
 
 
 
 
 
  Summary: As we suspect, the Require_once method does not load the same file multiple times. However, mixing with require will invalidate the Require_once method.  
 
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