Date library

自己写一个简单的：

#pragma once

// for linux nanoseconds, use:
// int clock_getcpuclockid(pid_t pid, clockid_t *clock_id);

#ifdef LINUX
#include <sys/time.h>
#else
#if (!defined _INC_WINAPIFAMILY)
#include <Windows.h>
#endif
#endif


class StopWatch
{
public:
    StopWatch()
#ifdef LINUX
        : timer(0)
#else
        : elapsed_(0)
#endif
    {
#ifdef LINUX
#else
        QueryPerformanceFrequency(&freq_);
#endif
    }
    ~StopWatch() {}
public:
    void start()
    {
#ifdef LINUX
        gettimeofday(&start, NULL);
#else
        QueryPerformanceCounter(&begin_time_);
#endif
    }
    void stop()
    {
#ifdef LINUX
        gettimeofday(&end, NULL);
        timer = 1000000 * (end.tv_sec - start.tv_sec) + end.tv_usec - start.tv_usec;
#else
        LARGE_INTEGER end_time;
        QueryPerformanceCounter(&end_time);
        elapsed_ += (end_time.QuadPart - begin_time_.QuadPart) * 1000000 / freq_.QuadPart;
#endif
    }
    void restart()
    {
#ifdef LINUX
        timer = 0;
#else
        elapsed_ = 0;
#endif
        start();
    }
    //微秒
    double elapsed() const
    {
#ifdef LINUX
        return static_cast<double>(timer);
#else
        return static_cast<double>(elapsed_);
#endif
    }
    //毫秒
    double elapsed_ms() const
    {
#ifdef LINUX
        return static_cast<double>(timer) / 1000.0;
#else
        return static_cast<double>(elapsed_) / 1000.0;
#endif
    }
    //秒
    double elapsed_second() const
    {
#ifdef LINUX
        return static_cast<double>(timer) / 1000000.0;
#else
        return static_cast<double>(elapsed_) / 1000000.0;
#endif
    }

private:
#ifdef LINUX
    struct  timeval  start;
    struct  timeval  end;
    unsigned long timer;
#else
    LARGE_INTEGER freq_;
    LARGE_INTEGER begin_time_;
    long long elapsed_;
#endif
};