Is this pointer initialization necessary?

Question

Lets say I have the following:

 CHARLINK * _init_link(CHARLINK **link)
 {
    short i;
    (*link)->cl = (CHARLINK **) calloc(NUM_CHARS, sizeof(CHARLINK *));
    for (i = 0; i < NUM_CHARS; i++)
        (*link)->cl[i] = NULL;
    return (*link);
}

Is the loop to initialize each element to NULL necessary or are they automatically NULL from calloc?

Answer 1

No, calloc initializes its buffers to 0's.

Answer 2

That depends a bit on your system, but in the vast majority of cases it's ok. calloc() returns you a buffer filled with zeros. However, the null pointer on your machine might not be a bit pattern of 0. On a machine where the null pointer is non-zero, you might end up in trouble.

Answer 3

Yes, the assignment to NULL in the loop is necessary. calloc initialises to all bits 0. But a null pointer may not be represented like that. It is implementation dependent. Thus the assignment is necessary.