C++11

#include <thread>

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

参考：std::thread::hardware_concurrency

在 C11 之前的 C 中，没有可移植的方式。相反，您需要使用以下一种或多种方法（由适当的#ifdef行保护）：

• Win32

  SYSTEM_INFO sysinfo;
  

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

• Linux、Solaris、AIX 和 Mac OS X >=10.4（即 Tiger 以后）

  int numCPU = sysconf(_SC_NPROCESSORS_ONLN);
  

• FreeBSD、MacOS X、NetBSD、OpenBSD 等。

  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 或 iOS)

  NSUInteger a = [[NSProcessInfo processInfo] processorCount];
  

  NSUInteger b = [[NSProcessInfo processInfo] activeProcessorCount];