Detecting number of CPU

cpucount.c

// Copyright (c) 2016 Roman Chistokhodov
// Distributed under the Boost Software License, Version 1.0.
// http://www.boost.org/LICENSE_1_0.txt

#include <stdio.h>
#include <stddef.h>

#if defined(__unix__) || defined(__APPLE__)
#include <unistd.h>
#endif

#ifdef __linux__
#include <sched.h>
#endif

#if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__APPLE__)
#include <sys/types.h>
#include <sys/sysctl.h>

#define UseSysctlbyname
#endif

#ifdef _WIN32
#include <windows.h>
#endif

void printFail(const char* methodName)
{
    fprintf(stderr, "Could not detect number of CPU using %s\n", methodName);
}

void printSuccess(const char* methodName, int cpuNumber)
{
    fprintf(stdout, "Number of CPU according to %s: %d\n", methodName, cpuNumber);
}

int main(int argc, char** argv)
{
#if defined(__unix__) || defined(__APPLE__)
#ifdef _SC_NPROCESSORS_ONLN
    long sysconfResult = sysconf(_SC_NPROCESSORS_ONLN);
    if (sysconfResult < 1) {
        printFail("_SC_NPROCESSORS_ONLN");
    } else {
        printSuccess("_SC_NPROCESSORS_ONLN", (int)sysconfResult);
    }
#else
    fprintf(stdout, "_SC_NPROCESSORS_ONLN is not available\n");
#endif
#endif
    
#ifdef __linux__
#ifdef _GNU_SOURCE
    cpu_set_t cs;
    CPU_ZERO(&cs);
    if (sched_getaffinity(0, sizeof(cs), &cs) != 0) {
        printFail("sched_getaffinity");
    } else {
        int i;
        int count = 0;
        for (i = 0; i < CPU_COUNT(&cs); i++)
        {
            if (CPU_ISSET(i, &cs))
                count++;
        }
        printSuccess("CPU_ISSET", count);
    }
#else
    fprintf(stdout, "Compile with -D_GNU_SOURCE to enable detection via CPU_ISSET\n");
#endif
#endif
    
#ifdef UseSysctlbyname
#ifdef __APPLE__
    const char* name = "machdep.cpu.core_count";
#else
    const char* name = "hw.ncpu";
#endif
    
    unsigned int number;
    size_t len = sizeof(unsigned int);
    sysctlbyname(name, &number, &len, NULL, 0);
    
    if (number < 1) {
        printFail("sysctlbyname");
    } else {
        printSuccess("sysctlbyname", (int)number);
    }
#endif

#ifdef _WIN32
    SYSTEM_INFO info;
    GetSystemInfo(&info);
    if (info.dwNumberOfProcessors < 1) {
        printFail("GetSystemInfo");
    } else {
        printSuccess("GetSystemInfo", (int)info.dwNumberOfProcessors);
    }
#endif
    
    return 0;
}