Summary of how to use php require_once

php require_once function can reference another file, and can achieve the purpose of referencing the file. The following article will give you a detailed understanding of how to use the php require_once function. I hope it will be helpful to you.

Recommended manual: php complete self-study manual

require_once statement is exactly the same as require statement , the only difference is that PHP will check whether the file has already been included, and if so, it will not include it again.

See the documentation of include_once to understand the meaning of _once and understand the difference from when there is no _once.

There is a file a.php, which has a variable $var=1; I used the require_once() function in b.php to reference the a.php file, and then I used require_once() in c.php ) refers to the b.php file. There is a function in c.php that needs to reference the variable $var in a.php. But the value of the variable cannot be accessed and is empty.
What should I do if I want to access the variable $var.

require_once() To avoid loading files repeatedly. Meaning: Load file once

require_once() statement includes and runs the specified file during script execution. This behavior is similar to the require() statement, the only difference is that if the code in the file is already included, it will not be included again.

is generally used when including files. For example, if you write a class file a.php, this file mainly defines classes. The code may be as follows:

class p
{
 public $a;
 function make(}
 {
  echo $a;
 }
}

At this time, you are in file b To use this class in .php, you can add require_once(a.php); at the beginning of b.php to load this a.php, which is equivalent to copying the code of the a.php file into b.php. .

Similar methods include require(), include(), and include_once(). The methods with the word _once are declared to be loaded only once, because you may already require_once(a) in other files of require_once(). .php), if it is loaded again, it will cause repeated loading, the amount of code will increase, and the parsing will slow down.

I have tested it for you, there is no problem, just require_once

a.php:

<?php
$a=123;
?>

b.php:

<?php
require_once("a.php");
?>

c.php:

<?php
require_once("b.php");
echo $a;
?>

Check your code and see if there is any minor problem

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