free() same heap memory with different pointers

Question

int main()
{
    int* Pointer;

    Pointer = (int*) malloc(sizeof(int));
    *Pointer = 33;

    int* Pointer2 = Pointer;

    printf("%d\n", *Pointer);

    free(Pointer);
    free(Pointer2);

    return 0;
}

The output is 33 with no errors or warnings. I declared two pointers that are pointing to the same heap address. I know it's wrong to free them both and it is sufficient to only free one. Is it undefined if I free them both and will it do anything wrong if I free the same heap area from different pointers (Pointer and Pointer2)?

Answer 1

As per the C11 standard draft 7.22.3.3p2

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. Otherwise, if the argument does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined.

(The emphasis is mine..)