using calloc to create bitmap in C

Question

If I use an int array as my bitmap, the size I allocate will be (1<<28)/32 right? because int is 32 bits...? And if I want to calloc this space before any functions are called, do I have to do anything special? Edit

I am trying to use calloc to have a bit array where I am able to check and set bits at that array location.

my attempt:

    int bitmap[] = calloc(1<<28, 1);

and

    int bitmap[] = (int*) calloc(1<<28, 1);

I am not sure what type the bitmap is or what to cast calloc to...

Any help would be appreciated!

Answer 1

You can't work directly with a "bit array" in C. You need to use masking / bitshift operators to access individual bits in larger units (at least an 8-bit char).

Also, the correct syntax for what you're attempting is:

int *bitmap = calloc(1<<28, sizeof(int));

which will allocate an array of (1<<28) ints.

Access them like this:

int i;
for (i = 0; i < (1<<28); ++i) {
    bitmap[i] = ...
}