Windows Server 2003及以后版本允许您利用GetLogicalProcessorInformation函数

http://msdn.microsoft.com/en-us/library/ms683194.aspx

这个功能是c++ 11标准的一部分。

#include <thread>

unsigned int nthreads = std::thread::hardware_concurrency();

对于较老的编译器，可以使用Boost。线程库。

#include <boost/thread.hpp>

unsigned int nthreads = boost::thread::hardware_concurrency();

在任何一种情况下，hardware_concurrency()都会根据CPU内核和超线程单元的数量返回硬件能够并发执行的线程数。

关于OS X的更多信息:sysconf(_SC_NPROCESSORS_ONLN)仅在>= 10.5版本可用，而不是10.4版本。

另一种方法是HW_AVAILCPU/sysctl() BSD代码，在>= 10.2版本中可用。

Win32:

GetSystemInfo()获取逻辑处理器的数量，使用 GetLogicalProcessorInformationEx () 来获取物理处理器的数量。

Note that "number of cores" might not be a particularly useful number, you might have to qualify it a bit more. How do you want to count multi-threaded CPUs such as Intel HT, IBM Power5 and Power6, and most famously, Sun's Niagara/UltraSparc T1 and T2? Or even more interesting, the MIPS 1004k with its two levels of hardware threading (supervisor AND user-level)... Not to mention what happens when you move into hypervisor-supported systems where the hardware might have tens of CPUs but your particular OS only sees a few.

最好的情况是告诉您在本地OS分区中拥有的逻辑处理单元的数量。除非您是管理程序，否则不要考虑看到真正的机器。今天这个规则唯一的例外是在x86领域，但非虚拟机的末日很快就会到来……

(几乎)c代码中的平台独立函数

#ifdef _WIN32
#include <windows.h>
#elif MACOS
#include <sys/param.h>
#include <sys/sysctl.h>
#else
#include <unistd.h>
#endif

int getNumCores() {
#ifdef WIN32
    SYSTEM_INFO sysinfo;
    GetSystemInfo(&sysinfo);
    return sysinfo.dwNumberOfProcessors;
#elif MACOS
    int nm[2];
    size_t len = 4;
    uint32_t count;

    nm[0] = CTL_HW; nm[1] = HW_AVAILCPU;
    sysctl(nm, 2, &count, &len, NULL, 0);

    if(count < 1) {
        nm[1] = HW_NCPU;
        sysctl(nm, 2, &count, &len, NULL, 0);
        if(count < 1) { count = 1; }
    }
    return count;
#else
    return sysconf(_SC_NPROCESSORS_ONLN);
#endif
}