Programmatically find the number of cores on a machine

Question

Is there a way to determine how many cores a machine has from C/C++ in a platform-independent way? If no such thing exists, what about determining it per-platform (Windows/*nix/Mac)?

Answer 1

C++11

#include <thread>  //may return 0 when not able to detect const auto processor_count = std::thread::hardware_concurrency(); 

Reference: std::thread::hardware_concurrency

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In C++ prior to C++11, there's no portable way. Instead, you'll need to use one or more of the following methods (guarded by appropriate #ifdef lines):

• Win32

  SYSTEM_INFO sysinfo; GetSystemInfo(&sysinfo); int numCPU = sysinfo.dwNumberOfProcessors; 

• Linux, Solaris, AIX and Mac OS X >=10.4 (i.e. Tiger onwards)

  int numCPU = sysconf(_SC_NPROCESSORS_ONLN); 

• FreeBSD, MacOS X, NetBSD, OpenBSD, etc.

  int mib[4]; int numCPU; std::size_t len = sizeof(numCPU);   /* set the mib for hw.ncpu */ mib[0] = CTL_HW; mib[1] = HW_AVAILCPU;  // alternatively, try HW_NCPU;  /* get the number of CPUs from the system */ sysctl(mib, 2, &numCPU, &len, NULL, 0);  if (numCPU < 1)  {     mib[1] = HW_NCPU;     sysctl(mib, 2, &numCPU, &len, NULL, 0);     if (numCPU < 1)         numCPU = 1; } 

• HPUX

  int numCPU = mpctl(MPC_GETNUMSPUS, NULL, NULL); 

• IRIX

  int numCPU = sysconf(_SC_NPROC_ONLN); 

• Objective-C (Mac OS X >=10.5 or iOS)

  NSUInteger a = [[NSProcessInfo processInfo] processorCount]; NSUInteger b = [[NSProcessInfo processInfo] activeProcessorCount];