C++ 计算时间差的五种方法小结

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 <编程客栈;QTime>
#include <sys/time.h>  //clock, gettimeofday, time
#include <ouXbFaXGmkWindows.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);
  QandroidTime stopTime = QTjavascriptime::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, st开发者_开发教程opCount;
  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.QuadPa编程客栈rt;
    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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