[scott_s]

Hmm. The question "what is the size of memory that x points to?" is cheap to figure out, because free needs to do it anyway. You couldn't use a macro to do it - it would need to access the internal data structures of the allocator - but it's easy to do. The other questions could be macros that called the first function.

What are the use cases for these functions? What bugs would they prevent?

[tptacek]

Worth pointing out again: the size of the chunk allocated for a particular data structure does not give you the precise bounds of the data structure; odds are, the chunk is slightly larger than the structure.

[scott_s]

I wrote a response explaining why, if you know x then you must know y, but then I realized you were talking about knowing y and learning x. Yes, I agree. I'm not sure which context (knowing the actual size of the memory chunk, which is easy, or knowing the used size of the memory chunk, which is not easy) Zed was talking about.