Question

I wanted to ask, if I have a pointer pointing at some struct, but then I free(struct) then if I dereference the pointer, will it be pointing to NULL? As in can I check, pointer != NULL or is this undefined?

Thanks!

Answer 1

Calling free() on the pointer does not change the pointer value. It will still point to the same memory that no longer belongs to your application. You should always assign NULL to a free’d pointer immediately after you free it to ensure that you don’t use it again.

void *p = malloc(10);    // p points to allocated memory
free(p);                 // p still points to invalid memory
p = NULL;                // good practice