Are dev_t and ino_t required to be integer types?

Question

The documentation for glibc stays they are integer types (no narrower than unsigned int), but I'm not finding a standards reference that says they have to be an integer type (see also time_t).

So in the end, the question becomes: Is

#include <stdio.h>
#include <stdint.h>
struct stat st;

if (stat("somefile", &st) == 0) {
        printf("%ju %ju\n", (uintmax_t)st.st_dev, (uintmax_t)st.st_ino);
}

portable.

Answer 1

POSIX standard requires dev_t to be an integer type and ino_t to be an unsigned integer.

dev_t shall be an integer type.

fsblkcnt_t, fsfilcnt_t, and ino_t shall be defined as unsigned integer types.

Since intmax_t and uintmax_t are supposed to be the "greatest width" integers, your code is safe. Just to be sure in case st_dev happens to be negative, you could write it as:

    printf("%jd %ju\n", (intmax_t)st.st_dev, (uintmax_t)st.st_ino);

Otherwise, your code is safe.

Answer 2

From the current POSIX specifications:

dev_t shall be an integer type.

[...]

ino_t shall be defined as unsigned integer types