Find the number of CPU Cores, for Windows, Mac or Linux source code

This snippet submitted by Dirk-Jan Kroon on 2010-06-09. It has been viewed 45687 times.
Rating of 6.5 with 150 votes

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

int getNumberOfCores() {
#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
}

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