Understanding PHP File Inclusion Methods

Including external files in a PHP script is a common practice which leads to more organized, maintainable, and reusable code. There are various methods to include a file, such as require, include, require_once, and include_once. But, not all function equally especially when the file is missing.

The correct answer to the question "What is the correct way to include a file in PHP without causing a fatal error if the file is missing?" is include('file.php');.

The include() function is used to include and evaluate a specific file. If the file is not found or can't be included for some reason, PHP will emit a warning (E_WARNING) but the script will continue to execute. This makes include() suitable for cases where the missing file isn't crucial and the application can still function properly without it.

Here's a practical example:

<?php
echo "Hello, World!";

// Including a non-existent file
@include('non_existing_file.php');

echo "This will still be printed.";
?>

In this case, despite the missing file, the script will not terminate but just issue a warning.

This is different from the require() function, which behaves similarly to include(), but instead of just issuing a warning, it will cause a fatal error (E_COMPILE_ERROR) and halt the script if the file is not found.

The include_once() and require_once() functions behave like their counterparts (include() and require()) but they also check if the file has already been included before, and if so, they do not include it again.

Best practice advises that it's better to use require or require_once when the file being included is crucial to the application, like a file containing needed functions. Include or include_once is more appropriate when the file is not critical to the application and the absence of the file can be handled gracefully by the application. In this context, include('file.php'); is the correct choice as it won't cause a fatal error if the file is missing.