[kevin_thibedeau]

You just feed sizeof the instance of the object you're allocating memory for. That entails funky pseudo-dereferences for pointers so the compiler doesn't give you the size of a pointer. It will look up the object's type and requisite size to fill in the argument to malloc(). If the object in question has an unknown type (maybe all you've got is a void *) then you will have to provide the size by other means.