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

还有一个Windows秘方:使用系统范围的环境变量NUMBER_OF_PROCESSORS:

printf("%d\n", atoi(getenv("NUMBER_OF_PROCESSORS")));

(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
}

在linux上，据我所知，最好的编程方式是使用

sysconf(_SC_NPROCESSORS_CONF)

or

sysconf(_SC_NPROCESSORS_ONLN)

这些不是标准的，但是在我的Linux手册页中。

与c++无关，但在Linux上我通常这样做:

grep processor /proc/cpuinfo | wc -l

适用于bash/perl/python/ruby等脚本语言。

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……