The clock_getres function obtains the resolution value for the
    specified clock. Clock resolutions are implementation-dependent
    and cannot be set by a process.

    If the res argument is not NULL, the resolution of the specified
    clock is stored in the location pointed to by res.

    If res is NULL, the clock resolution is not stored.

    If the time argument (tp) of clock_settime is not a multiple of
    res, then the value is truncated to a multiple of res.

    On success, the function returns 0.

    On failure, the function returns -1 and sets errno to indicate
    the error.

    See also clock_gettime, clock_settime, time, and ctime.