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

Question

Is there an API to get the number of CPUs available in Linux? I mean, without using /proc/cpuinfo or any other sys-node file...

I\'ve found this implementation using

Answer 1

None of the answers that involve sysconf(...) or get_nprocs() are correct for honouring the number of processors restricted to a task by cpu affinity.

You need something like this to get the number of processors available to a task:

#define _GNU_SOURCE
#include 
#include 

int nprocs()
{
  cpu_set_t cs;
  CPU_ZERO(&cs);
  sched_getaffinity(0, sizeof(cs), &cs);
  return CPU_COUNT(&cs);
}

int main()
{
  printf("procs=%d\n", nprocs());
  return 0;
}