php: The difference between require_once and require

Difference:

require_once will only load the same file once, while require will load it multiple times.

I believe that novices like me still have some doubts. So we guessed: If 456.php introduced 123.php, now the file test_require.php introduces "456.php" and "123.php". If the require method is used, then in test_require.php, 123.php will be introduced twice, and using therequire_oncemethod 123.php will be introduced once. So let’s do the experiment!

1. require method

The content of 123.php is as follows:

        

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The content of 456.php is as follows:

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 require("123.php");  echo "456\n";

        

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2. require_once method

123.php content remains unchanged. 456.php and test_require.php change the require_once method. The content is as follows:

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//456.php 
        

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//123.php 
         

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