c - freeing a null pointer

Question

What happens inside memory if we try to free a pointer which is pointing to NULL? Is that ever valid?

Why does it not show any warning/error messages?

Answer 1

From C99 section 7.20.3.2 : The free function

Synopsis

 1 #include <stdlib.h>
   void free(void *ptr);

Description

2 The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs.