c - Any function to query the size of an allocated block?

Question

I realize that any such function is likely to be non standard, but that's ok for my use case. Basically, I need a method (even if it's only exposed through glibc's syscall() interface) that I can pass a pointer to (a pointer that was returned by a previous call to malloc()) that returns the size of the block the pointer points at. Does such a thing exist?

Answer 1

So far as I know, there is no such function at least in C90/C99. Some systems, mostly libc, provide functions to get allocated size (e.g. malloc_size() in Mac OS X), but this is not portable and probably you should avoid using that at best.