C: stat does not show filesize properly for large files

Question

I have a simple function to print file size and file name:

void *mystat(void *filename) {

    struct stat fileStat;

    if (lstat(filename,&fileStat) < 0) {
        fprintf(stderr, "no such file or directory: %s\n", filename);
        return NULL;
    }

    printf(" %'d",fileStat.st_size);

    printf(" %s\n", filename);
}

it works fine for small files, but when file is large (couple of GB) it prints size 0.

Why is this not working for large files ?

EDIT

Actually it only prints file size 0 when the file size is multiple of 4GB. In other case, when file is large but not multiple, it prints negative number.

but, when I capture the return code of lstat and print it, it is 0:

ret = lstat(filename,&fileStat)

I am compiling and running my code on a 64-bit system.

Obviously, the fileStat.st_size is overflowing, but why?

Answer 1

lstat is giving you the right answer. It's printf that's the problem. Use %'ld instead of %'d to be good enough in practice, or if you want to be pedantically correct, then do this instead:

printf(" %'jd", (intmax_t)fileStat.st_size);

You may also need to #include <stdint.h>, if you get an error that intmax_t doesn't exist.