What is the use of include_once in PHP?

The functionality of include_once in PHP is designed specifically to include a file just once during the execution of a script. When you use include_once, PHP checks if the file has already been included in the script before; if it has, it will not include it again. This behavior is crucial for preventing issues that arise from function redefinitions, variable reassignment, or duplicate code execution, which can lead to errors or undesired behavior in the application.

While the phrase "to ensure a file is included at least once" might seem a bit ambiguous, it implies safeguarding against multiple inclusions, which include_once effectively accomplishes. Including a file at least once ensures that any defined functions, classes, or variables are available for use throughout the execution of the script without the risk of them being declared more than once.

This behavior is particularly important in larger applications or when working with libraries, where including the same file multiple times could cause conflicts or generate fatal errors.

The other options do not fully encapsulate the specific purpose of include_once, which is to ensure safe file inclusion without redundancy while preventing potential errors from occurring in the application's workflow.