statfs on macOS doesn't give me full disk capacity. Why?

Question

I'm trying to get the storage drive capacity and the free space on it from my macOS app.

I do the following:

struct statfs stStg;

if(statfs(".", &stStg) == 0)
{
    uint64_t total_sz = stStg.f_bsize * stStg.f_blocks;
    uint64_t free_sz = stStg.f_bsize * stStg.f_bfree;

    double fTotal = (double)total_sz / (1024.0 * 1024.0 * 1024.0);
    double fFree = (double)free_sz / (1024.0 * 1024.0 * 1024.0);

    printf(""%.02f GB (%.01f%% free)"
                 ,
                 fTotal,
                 100.0 * fFree / fTotal);
}

It gives me:

460.43 GB (66.5% free)

But when I check it in Finder, I'm getting a larger capacity:

What am I doing wrong?

Answer 1

1024.0 * 1024.0 * 1024.0 B is GiB, not GB. These are two different units. GB is 1000 * 1000 * 1000 B.

1024 * 1024 * 1024 / (1000 * 1000 * 1000) * 460.43 GiB = 494.38 GB

For more information, see Wikipedia