How do I retrieve the number of processors on C / Linux?
As others have mentioned in comments, this answer is useful:
numCPU = sysconf( _SC_NPROCESSORS_ONLN );Leaving as a solution for folks that might skip over comments...
Why not use sys/sysinfo.h?
#include <sys/sysinfo.h>#include <stdio.h>void main () { printf ("You have %d processors.\n", get_nprocs ());}Way more information can be found on the man page
$ man 3 get_nprocs
machine:/sys/devices/system/cpu$ lscpu0 cpu3 cpu6 kernel_max perf_counters sched_mc_power_savingscpu1 cpu4 cpu7 offline possiblecpu2 cpu5 cpuidle online presentIf you have a machine with sysfs, take a look in /sys/devices/system/cpu.
Make sure you're asking for what you want -- CPUs, cores, hyperthreads, etc.