allocating memory

have this pointer
Char *ptr
i allocate memory as
ptr = (char *) malloc (sizeof(char) * 100);
say later on in the program i may or may not need to store more characters so i'll use realloc to assign more memory. How can i find out how much memory is currently assigned to ptr so i cant find if i need to resize it or not.

>>17
Ah, so Sepples' pointers can be different sizes. Great. That's why Sepples requires casts to/from void*, and C doesn't, because in C all pointers are the same size.

OK, people, we've solved it. Nothing to see here.