C++ 求时差

C++ 求时差的三种方法

【1】标准C库方式

示例代码

#include <ctime>
#include <iostream>
using namespace std;

void function()
{
    int step = 100000000;
    while (step--);
}

int main()
{
    clock_t start = clock();  //获取当前系统时间

    function();

    clock_t end = clock();

    double cost = ((double)(end - start)) / CLOCKS_PER_SEC;

    cout << "cost time : " << cost << endl;

    system("pause");
}

/* result:
cost time : 0.166
请按任意键继续. . .
*/

【2】C++库方式

C++11之后才引入

示例代码：

#include <chrono>
#include <iostream>

using namespace std;

void function()
{
    int step = 100000000;
    while (step--);
}

int main() 
{
    auto beginTime = std::chrono::high_resolution_clock::now();

    function();

    auto endTime = std::chrono::high_resolution_clock::now();
    auto elapsedTime = std::chrono::duration_cast<std::chrono::microseconds>(endTime - beginTime);

    double cost = (double)elapsedTime.count();

    cout << "cost time : " << cost << endl;

    system("pause");
}

/* result:
cost time : 164445
请按任意键继续. . .
*/

【3】windows API方式

示例代码：

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

using namespace std;

void function()
{
    int step = 100000000;
    while (step--);
}

int main()
{
    //DWORD dwStart = GetTickCount();

    ULONGLONG dwStart = GetTickCount64();

    function();

    ULONGLONG dwEnd = GetTickCount64();
    
    auto cost = (dwEnd - dwStart);

    cout << "cost time : " << cost << endl;

    system("pause");
}

/* result:
cost time : 157
请按任意键继续. . .
*/

为什么第14行，我们把GetTickCount这个函数注释了呢？请参见Visual Studio 提示内容：