六种c++计时器函数（秒级到微妙级）

以下所有代码都有使用Sleep（）延时函数，需 #include <Windows.h>

1.使用clock()，ms级别计时器 ：

        double start = clock();
	Sleep(1000);
	double end = clock();
	double last = start - end;
	cout << last << "ms" << endl;

使用时需要包含头文件<ctime>

2. 使用GetTickCount()，ms级别计时器 ：

        double start = GetTickCount(); //计时器
	Sleep(2000);
	double end = GetTickCount();
        double last = start - end;
	cout << last << "ms" << endl;

使用时需包含<Window.h>

3.使用getTickCount()，ms级别计时器：

        double start = getTickCount();//开始时间
	Sleep(2000);
	double end = getTickCount();
	double last = (end - start) * 1000 / getTickFrequency();
	cout << last << "ms" << endl;

这是opencv 所带计时器，使用时需#include <opencv2/opencv.hpp>，前面那个GetTickCount()是win的API。

4.使用time(NULL)，s级别计时器：

        double start, stop, durationTime;
	start = time(NULL);
	Sleep(2000);
	stop = time(NULL);
	durationTime = (double)difftime(stop, start);
	cout << "程序耗时：" << durationTime << " s" << endl;

需要包含<ctime> 

5.微秒级计时器QueryPerformance：

        LARGE_INTEGER cpuFreq;
	LARGE_INTEGER startTime;
	LARGE_INTEGER endTime;
	
	QueryPerformanceFrequency(&cpuFreq);
	QueryPerformanceCounter(&startTime);
	Sleep(1000);
	QueryPerformanceCounter(&endTime);
	double last = (((endTime.QuadPart - startTime.QuadPart) * 1000000) / cpuFreq.QuadPart);
	cout << last << " us" << endl;

需要包含<Windows.h> 

还可以将其封装为一个类：

class stop_watch
{
public:
	stop_watch()
		: elapsed_(0)
	{
		QueryPerformanceFrequency(&freq_);
	}
	~stop_watch() {}
public:
	void start()
	{
		QueryPerformanceCounter(&begin_time_);
	}
	void stop()
	{
		LARGE_INTEGER end_time;
		QueryPerformanceCounter(&end_time);
		elapsed_ += (end_time.QuadPart - begin_time_.QuadPart) * 1000000 / freq_.QuadPart;
	}
	void restart()
	{
		elapsed_ = 0;
		start();
	}
	//微秒
	double elapsed()
	{
		return static_cast<double>(elapsed_);
	}
	//毫秒
	double elapsed_ms()
	{
		return elapsed_ / 1000.0;
	}
	//秒
	double elapsed_second()
	{
		return elapsed_ / 1000000.0;
	}

private:
	LARGE_INTEGER freq_;
	LARGE_INTEGER begin_time_;
	long long elapsed_;
};

int main()
{
	stop_watch watch;
	watch.start();
	Sleep(2000);
	watch.stop();
	cout << watch.elapsed() << endl;
}

6.C++11 chrono库，微秒级别计时器

        auto start = steady_clock::now();

	Sleep(1000);

	auto end = steady_clock::now();

	auto last = duration_cast<microseconds>(end - start);

	cout <<  last.count() << "um";

需要包含头文件 #include <chrono>并且using namespace std::chrono;