$ cat f.c
#include <stdio.h>
extern int __get_nprocs_sched (void);

int main() {
        printf("%d\n", __get_nprocs_sched());
}
$ gcc -static f.c -o f
$ ./f
828
$ ./f
794
$ nproc
8

sched_getaffinity(2) writes first N bits of cpu_bits array, but the rest of it is left uninitialized.