Is Checking for \"this\" Nullity Ever Justified in C ?

Is Checking for "this" Nullity Ever Justified?

In the realm of object-oriented programming, the concept of "this," often synonymous with the notion of the current object, plays a crucial role. However, a question that arises in this context is whether it ever makes sense to check if "this" is null.

Original Question:

In a class with member functions, a developer poses the question:

"If I have a method with the condition "this == nullptr" inside it, and if the result is true, I'm instructed to return an error code. If "this" is indeed null, indicating that the object has been deleted, can the method still produce any output?"

Standard C Perspective:

In standard C , the answer is a resounding no. Calls made on null pointers are, by definition, undefined behavior. Any code that relies on checks for "this" == null is non-standard. It's crucial to note that this applies to non-virtual functions as well.

Exceptions in Specific Implementations:

Some C implementations allow for "this == 0," creating a caveat to the standard behavior. Libraries designed specifically for such implementations may utilize this condition as a hack, as exemplified by the pairing of VC with MFC.

Other Considerations:

Beyond the strict implementation rules, other factors may contribute to the existence of "this" == null checks. Some instances may serve as debugging aids, catching errors when the condition was previously encountered due to coding errors in the caller. Asserts are generally preferable for this purpose, providing a more appropriate mechanism for detecting such situations.

Conclusion:

In the context of standard C , checking for "this" == null is not justified. Method calls on null pointers are inherently undefined behavior, rendering any reliance on such checks unreliable. If encountered during code review, these checks should be scrutinized and potentially replaced with more suitable error-handling mechanisms.

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