How to get the number of CPUs in Linux using C?

#include <unistd.h>long number_of_processors = sysconf(_SC_NPROCESSORS_ONLN);

#include <stdio.h>#include <sys/sysinfo.h>int main(int argc, char *argv[]){    printf("This system has %d processors configured and "        "%d processors available.\n",        get_nprocs_conf(), get_nprocs());    return 0;}

https://linux.die.net/man/3/get_nprocs

This code (drawn from here) should work on both windows and *NIX platforms.

#ifdef _WIN32#define WIN32_LEAN_AND_MEAN#include <windows.h>#else#include <unistd.h>#endif#include <stdio.h>#include <stdlib.h>#include <string.h>#include <errno.h>int main() {  long nprocs = -1;  long nprocs_max = -1;#ifdef _WIN32#ifndef _SC_NPROCESSORS_ONLNSYSTEM_INFO info;GetSystemInfo(&info);#define sysconf(a) info.dwNumberOfProcessors#define _SC_NPROCESSORS_ONLN#endif#endif#ifdef _SC_NPROCESSORS_ONLN  nprocs = sysconf(_SC_NPROCESSORS_ONLN);  if (nprocs < 1)  {    fprintf(stderr, "Could not determine number of CPUs online:\n%s\n", strerror (errno));    exit (EXIT_FAILURE);  }  nprocs_max = sysconf(_SC_NPROCESSORS_CONF);  if (nprocs_max < 1)  {    fprintf(stderr, "Could not determine number of CPUs configured:\n%s\n", strerror (errno));    exit (EXIT_FAILURE);  }  printf ("%ld of %ld processors online\n",nprocs, nprocs_max);  exit (EXIT_SUCCESS);#else  fprintf(stderr, "Could not determine number of CPUs");  exit (EXIT_FAILURE);#endif}