int res = 0;
int nval = -1;

errno = 0;
res = nice(nval);

#ifdef 1
if ((-1 == res) && (errno != 0))
#else
if (errno != 0)
#endif
{
    fprintf(stderr, "failed to set nice %d: %s\n", nval, strerror(errno));
    exit(-1);
}

printf("priority is %d\n", res)