C++ Windows时间函数 QueryPerformanceCounter()与QueryPerformanceFrequency()

介绍

供WIN9X使用的高精度定时器：QueryPerformanceFrequency()和QueryPerformanceCounter()，要求计算机从硬件上支持高精度定时器。头文件为 windows.h头。

函数的原形是：

BOOL QueryPerformanceFrequency(LARGE_INTEGER *lpFrequency); // 获取时钟频率
BOOL QueryPerformanceCounter (LARGE_INTEGER *lpCount); // 获取时钟计数值

数据类型LARGE_INTEGER既可以是一个作为8字节长的整数，也可以是作为两个4字节长的整数的联合结构，其具体用法根据编译器是否支持64位而定。该类型的定义如下：

typedef union _LARGE_INTEGER {
    
    
    struct {
    
    
        ULONG LowPart;
        LONG HighPart;
    } DUMMYSTRUCTNAME;
    struct {
    
    
        ULONG LowPart;
        LONG HighPart;
    } u;
#endif //MIDL_PASS
    LONGLONG QuadPart;
} LARGE_INTEGER;

在定时前应该先调用QueryPerformanceFrequency()函数获得机器内部计时器的时钟频率。接着在需要严格计时的事件发生前和发生之后分别调用QueryPerformanceCounter()，利用两次获得的计数之差和时钟频率，就可以计算出事件经历的精确时间。

测试程序

测试Sleep的精确时间：

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

int main()
{
    
    
	LARGE_INTEGER freq;
	LARGE_INTEGER beginTime;
	LARGE_INTEGER endTime;

	QueryPerformanceFrequency(&freq);
	QueryPerformanceCounter(&beginTime);
	std::this_thread::sleep_for(std::chrono::seconds(10));
	QueryPerformanceCounter(&endTime);
	int timeOfSecond = (double)(endTime.QuadPart - beginTime.QuadPart) / (double)freq.QuadPart;
	int timeOfMicroSecond = (double)(endTime.QuadPart - beginTime.QuadPart) * 1e6 / (double)freq.QuadPart;
	std::cout << timeOfSecond << " " << timeOfMicroSecond << std::endl;

	return 0;
}

一个封装类Timer(来自miloyip）

#include <windows.h>

class Timer {
    
    
public:
	Timer() : start_(), end_() {
    
    
	}

	void Start() {
    
    
		QueryPerformanceCounter(&start_);
	}

	void Stop() {
    
    
		QueryPerformanceCounter(&end_);
	}

	double GetElapsedMilliseconds() {
    
    
		LARGE_INTEGER freq;
		QueryPerformanceFrequency(&freq);
		return (end_.QuadPart - start_.QuadPart) * 1000.0 / freq.QuadPart;
	}

private:
	LARGE_INTEGER start_;
	LARGE_INTEGER end_;
};