Determine size of dynamically allocated memory in C

Question

Is there a way in C to find out the size of dynamically allocated memory?

For example, after

char* p = malloc (100);

Is there

Answer 1

Well now I know this is not answering your specific question, however thinking outside of the box as it were... It occurs to me you probably do not need to know. Ok, ok, no I don't mean your have a bad or un-orthodox implementation... I mean is that you probably (without looking at your code I am only guessing) you prbably only want to know if your data can fit in the allocated memory, if that is the case then this solution might be better. It should not offer too much overhead and will solve your "fitting" problem if that is indeed what you are handling:

if ( p != (tmp = realloc(p, required_size)) ) p = tmp;

or if you need to maintain the old contents:

if ( p != (tmp = realloc(p, required_size)) ) memcpy(tmp, p = tmp, required_size);

of course you could just use:

p = realloc(p, required_size);

and be done with it.