Question

Possible Duplicate:
C programming : How does free know how much to free?

In this snippet

void main() {
void *p = malloc(300);
printf("%d",sizeof(*p));
free(p);
}

How does free know much memory it is supposed release from the void pointer?

I figure, if there is an internal table/function, it should be available to find out sizes of any kind of objects, whereas the output of the printf is 1

Answer 1

malloc and free do their own hidden accounting so they can do the correct thing.

The reason the sizeof() does not use this accounting information is that sizeof() is a compile time operator, and the malloc/free information is not available until runtime.