如何总结计算时间差的五种方法？

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Qt计算时间的两种方法：QTime.elapsed(): ms, QTime.currentTime(): ms

C++计算时间的五种方法：clock(): ms, GetTickCount(): ms, gettimeofday(time_val*, NULL): us, QueryPerformanceFrequency(LARGE_INTEGER*), QueryPerformanceCounter(LARGE_INTEGER*)

Qt计算时间的两种方法：

• QTime elapsed() : ms
• QTime currentTime() : ms

C++计算时间的五种方法：

• clock() : ms
• GetTickCount() : ms
• gettimeofday(time_val*, NULL) : us
• QueryPerformanceFrequency(LARGE_INTEGER*) & QueryPerformanceCounter(LARGE_INTEGER*) : us
• time(NULL) : s

#include <QThread> #include <QTime> #include <sys/time.h>   //clock, gettimeofday, time #include <windows.h>    //Sleep, GetTickCount, timeGetTime, QueryPerformanceCounter #include <QDebug> //#pragma comment(lib, "winmm.lib") //timeGetTime, 但是这个库Windows或Qt或VS2015都没有自带 const unsigned long SLEEP_TIME_MILL = 1000; /**  * QTime的精度为ms级  */ void calcByQtimeElapsed() {     QTime time;     time.start();     QThread::msleep(SLEEP_TIME_MILL);     int timeElapsed = time.elapsed();     qDebug()<<"QTime.start & QTime.elspsed ="<<timeElapsed<<"ms"; } /**  * QTime的精度为ms级  */ void calcByQtimeCurrentTime() {     QTime startTime = QTime::currentTime();     QThread::msleep(SLEEP_TIME_MILL);     QTime stopTime = QTime::currentTime();     int elapsed = startTime.msecsTo(stopTime);     qDebug()<<"QTime.currentTime ="<<elapsed<<"ms"; } /**  * clock的精度为ms级  */ void calcByClock() {     clock_t startTime = clock();     Sleep(SLEEP_TIME_MILL);     clock_t endTime = clock();     clock_t elapsed = endTime - startTime;     qDebug()<<"clock ="<<elapsed<<"ms"; } /**  * GetTickCount的精度为ms级  */ void calcByTickCount() {     //返回自开机以来经历的毫秒数     DWORD startTime = GetTickCount();     Sleep(SLEEP_TIME_MILL);     DWORD stopTime = GetTickCount();     DWORD elapsed = stopTime - startTime;     qDebug()<<"GetTickCount = "<<elapsed<<"ms"; } ///** // * timeGetTime的精度为ms级 // * 必须添加Winmm.lib, 否则编译报错undefined reference // */ //void calcByTimeGetTime() { //    //返回自开机以来经历的毫秒数 //    DWORD startTime = timeGetTime(); //    Sleep(SLEEP_TIME_MILL); //    DWORD stopTime = timeGetTime(); //    DWORD elapsed = stopTime - startTime; //    qDebug()<<"timeGetTime = "<<elapsed<<"ms"; //} /**  * gettimeofday的精度为us级  */ void calcByGetTimeOfDay() {     struct timeval startTime, stopTime;     gettimeofday(&startTime, NULL);     Sleep(SLEEP_TIME_MILL);     gettimeofday(&stopTime, NULL);     long elapsed = (stopTime.tv_sec-startTime.tv_sec) * 1000000 + (stopTime.tv_usec - startTime.tv_usec);     qDebug()<<"gettimeofday ="<<elapsed<<"us"; } /**  * QueryPerformanceCounter的精度为us级  */ void calcByQueryPerformanceCounter() {     LARGE_INTEGER frequency, startCount, stopCount;     WINBOOL ret;     //返回性能计数器每秒滴答的个数     ret = QueryPerformanceFrequency(&frequency);     if(ret) {         ret = QueryPerformanceCounter(&startCount);     }     Sleep(SLEEP_TIME_MILL);     if(ret) {         QueryPerformanceCounter(&stopCount);     }     if(ret) {         LONGLONG elapsed = (stopCount.QuadPart - startCount.QuadPart) * 1000000 / frequency.QuadPart;         qDebug()<<"QueryPerformanceFrequency & QueryPerformanceCounter ="<<elapsed<<"us";     } } /**  * time(NULL)精确度为s级  */ void calcByTime() {     time_t startTime = time(NULL);     Sleep(SLEEP_TIME_MILL);     time_t stopTime = time(NULL);     long elapsed = stopTime - startTime;     qDebug()<<"time(NULL) ="<<elapsed<<"s"; } int main(int argc, char *argv[]) {     calcByQtimeElapsed();     calcByQtimeCurrentTime();     calcByClock();     calcByTickCount(); //    calcByTimeGetTime();     calcByGetTimeOfDay();     calcByQueryPerformanceCounter();     calcByTime();     system("pause");     return 0; }

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