Is this a good way to free memory?

Question

The function for freeing an instance of struct Foo is given below:

void DestroyFoo(Foo* foo)
{
    if (foo) free(foo);
}

A

Answer 1

Unfortunately, this idea is just not working.

If the intent was to catch double free, it is not covering cases like the following.

Assume this code:

Foo *ptr_1 = (FOO*) malloc(sizeof(Foo));
Foo *ptr_2 = ptr_1;
free (ptr_1);
free (ptr_2); /* This is a bug */

The proposal is to write instead:

Foo *ptr_1 = (FOO*) malloc(sizeof(Foo));
Foo *ptr_2 = ptr_1;
DestroyFoo (&ptr_1);
DestroyFoo (&ptr_2); /* This is still a bug */

The problem is that the second call to DestroyFoo() will still crash, because ptr_2 is not reset to NULL, and still point to memory already freed.