Explanation of include(), include_once(), require(), and require_once() in PHP

When working with PHP, these functions are commonly used to include files into your code. Here's a breakdown of the differences:

include()

The include() function includes and evaluates a specified file during the execution of the script. If the file is not found, a warning will be issued but the script will continue to run.

include_once()

The include_once() function works the same as include(), except that if the file has already been included, it will not be included again. This prevents errors that may arise from redefining functions or declaring classes multiple times.

require()

The require() function is similar to include() but with one key difference. If the specified file is not found, a fatal error will occur and the script will stop running.

require_once()

The require_once() function combines the behavior of require() and include_once(). It will include the file but ensure that it is only included once, similar to include_once().

It's important to choose the appropriate function based on your requirements to ensure the proper functioning of your PHP code.