一、前言

         这里记下从网上找到的一些自己比较常用的C++计时代码

二、Linux下精确至毫秒

#include <sys/time.h>
#include <iostream>
#include <time.h>
double get_wall_time()
{
    struct timeval time ;
    if (gettimeofday(&time,NULL)){
        return 0;
    }
    return (double)time.tv_sec + (double)time.tv_usec * .000001;
}

int main()
{
	unsigned int t = 0;
	double start_time = get_wall_time()
	while(t++<10e+6);
	double end_time = get_wall_time()
	std::cout<<"循环耗时为:"<<end_time-start_time<<"ms";
	return 0;
}

三、Windows下精确至毫秒

#include <windows.h>
#include <iostream>

int main()
{
	DWORD start, stop;
	unsigned int t = 0;
	start = GetTickCount();
	while (t++ < 10e+6);
	stop = GetTickCount();
	printf("time: %lld ms\n", stop - start);
	return 0;
}

试验中，发现貌似getTickCount函数会有10几毫秒的误差，囧。。。

四、Windows下精确至微秒

//MyTimer.h//
#ifndef __MyTimer_H__  
#define __MyTimer_H__  
#include <windows.h>  

class MyTimer
{
private:
	int _freq;
	LARGE_INTEGER _begin;
	LARGE_INTEGER _end;

public:
	long costTime;            // 花费的时间(精确到微秒)  

public:
	MyTimer()
	{
		LARGE_INTEGER tmp;
		QueryPerformanceFrequency(&tmp);//QueryPerformanceFrequency()作用：返回硬件支持的高精度计数器的频率。  

		_freq = tmp.QuadPart;
		costTime = 0;
	}

	void Start()            // 开始计时  
	{
		QueryPerformanceCounter(&_begin);//获得初始值  
	}

	void End()                // 结束计时  
	{
		QueryPerformanceCounter(&_end);//获得终止值  
		costTime = (long)((_end.QuadPart - _begin.QuadPart) * 1000000 / _freq);
	}

	void Reset()            // 计时清0  
	{
		costTime = 0;
	}
};
#endif  

//main.cpp
#include "MyTimer.h"
#include <iostream>


int main()
{
	MyTimer timer;
	unsigned int t = 0; 
	timer.Start();
	while (t++ < 10e+5);
	timer.End(); 
	std::cout << "耗时为：" << timer.costTime << "us";
	return 0 ;
}