QT： 一种精确定时器类的实现与使用

1）类的实现

#ifndef CPRECISETIMER_H
#define CPRECISETIMER_H

#include <windows.h>

class CPreciseTimer
{
public:
    CPreciseTimer();

    bool SupportsHighResCounter();
    void StartTimer();
    void StopTimer();
    __int64 GetTime();

private:
    //Auxiliary Function
    void UpdateElapsed();

    //Member variables
    bool m_bRunning;
    __int64 m_i64Start;
    __int64 m_i64Elapsed;

    //Some auxiliary variables
    __int64 m_i64Counts;
    LARGE_INTEGER m_liCount;

    //Static Variables
    static bool sm_bInit;
    static bool sm_bPerformanceCounter;
    static __int64 sm_i64Freq;
};

inline bool CPreciseTimer::SupportsHighResCounter()
{
    return sm_bPerformanceCounter;
}

//Auxiliary Function
inline void CPreciseTimer::UpdateElapsed()
{
    if(true == sm_bPerformanceCounter)
    {
        QueryPerformanceCounter(&m_liCount);
        m_i64Counts = ((__int64)m_liCount.HighPart << 32) + (__int64)m_liCount.LowPart;
        //Transform in microseconds
        (m_i64Counts *= 1000000) /= sm_i64Freq;
    }
    else
        //Transform milliseconds to microseconds
        m_i64Counts = (__int64)GetTickCount() * 1000;
    if(m_i64Counts > m_i64Start)
        m_i64Elapsed = m_i64Counts - m_i64Start;
    else
        //Eliminate possible number overflow (0x7fffffffffffffff is the maximal __int64 positive number)
        m_i64Elapsed = (0x7fffffffffffffff - m_i64Start) + m_i64Counts;
}

#endif // CPRECISETIMER_H

#include "cprecisetimer.h"

bool CPreciseTimer::sm_bInit = false;
bool CPreciseTimer::sm_bPerformanceCounter;
__int64 CPreciseTimer::sm_i64Freq;

//CONSTRUCTOR
CPreciseTimer::CPreciseTimer() : m_i64Start(0), m_i64Elapsed(0), m_bRunning(false)
{
    //Only if not already initialized
    if(false == sm_bInit)
    {
        //Initializing some static variables dependent on the system just once
        LARGE_INTEGER liFreq;
        if(TRUE == QueryPerformanceFrequency(&liFreq))
        {
            //Only if the system is supporting High Performance
            sm_i64Freq = ((__int64)liFreq.HighPart << 32) + (__int64)liFreq.LowPart;
            sm_bPerformanceCounter = true;
        }
        else
            sm_bPerformanceCounter = false;
        sm_bInit = true;
    }
}

void CPreciseTimer::StartTimer()
{
    if(true == sm_bPerformanceCounter)
    {
        QueryPerformanceCounter(&m_liCount);
        m_i64Start = ((__int64)m_liCount.HighPart << 32) + (__int64)m_liCount.LowPart;
        //Transform in microseconds
        (m_i64Start *= 1000000) /= sm_i64Freq;
    }
    else
        //Transform milliseconds to microseconds
        m_i64Start = (__int64)GetTickCount() * 1000;
    m_bRunning = true;
}

void CPreciseTimer::StopTimer()
{
    UpdateElapsed();
    m_bRunning = false;
}

__int64 CPreciseTimer::GetTime()
{
    if(true == m_bRunning)
        UpdateElapsed();
    return m_i64Elapsed;
}

2）类的使用

.......

CPreciseTimer preciseTimer;

// start the timer

preciseTimer.StartTimer();

//here do something ...

// Stop the timer

preciseTimer.StopTimer();

//get the time count

preciseTimer.GetTime();