How to get CPU info in C on Linux, such as number of cores? [duplicate]

Question

Is it possible to get such info by some API or function, rather than parsing the /proc/cpuinfo?

Answer 1

From man 5 proc:

   /proc/cpuinfo
          This is a collection of CPU and  system  architecture  dependent
          items,  for  each  supported architecture a different list.  Two
          common  entries  are  processor  which  gives  CPU  number   and
          bogomips;  a  system  constant  that is calculated during kernel
          initialization.  SMP machines have information for each CPU.

Here is sample code that reads and prints the info to console, stolen from forums - It really is just a specialized cat command.

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
   FILE *cpuinfo = fopen("/proc/cpuinfo", "rb");
   char *arg = 0;
   size_t size = 0;
   while(getdelim(&arg, &size, 0, cpuinfo) != -1)
   {
      puts(arg);
   }
   free(arg);
   fclose(cpuinfo);
   return 0;
}

Please note that you need to parse and compare the physical id, core id and cpu cores to get an accurate result, if you really care about the number of CPUs vs. CPU cores. Also please note that if there is a htt in flags, you are running a hyper-threading CPU, which means that your mileage may vary.

Please also note that if you run your kernel in a virtual machine, you only see the CPU cores dedicated to the VM guest.