C++ 求时差的三种方法

【1】标准C库方式

示例代码

 1 #include <ctime>
 2 #include <iostream>
 3 using namespace std;
 4 
 5 void function()
 6 {
 7     int step = 100000000;
 8     while (step--);
 9 }
10 
11 int main()
12 {
13     clock_t start = clock();  //获取当前系统时间
14 
15     function();
16 
17     clock_t end = clock();
18 
19     double cost = ((double)(end - start)) / CLOCKS_PER_SEC;
20 
21     cout << "cost time : " << cost << endl;
22 
23     system("pause");
24 }
25 
26 /* result:
27 cost time : 0.166
28 请按任意键继续. . .
29 */

【2】C++库方式

C++11之后才引入

示例代码：

 1 #include <chrono>
 2 #include <iostream>
 3 
 4 using namespace std;
 5 
 6 void function()
 7 {
 8     int step = 100000000;
 9     while (step--);
10 }
11 
12 int main() 
13 {
14     auto beginTime = std::chrono::high_resolution_clock::now();
15 
16     function();
17 
18     auto endTime = std::chrono::high_resolution_clock::now();
19     auto elapsedTime = std::chrono::duration_cast<std::chrono::microseconds>(endTime - beginTime);
20 
21     double cost = (double)elapsedTime.count();
22 
23     cout << "cost time : " << cost << endl;
24 
25     system("pause");
26 }
27 
28 /* result:
29 cost time : 164445
30 请按任意键继续. . .
31 */

【3】windows API方式

示例代码：

 1 #include <windows.h>
 2 #include <iostream>
 3 
 4 using namespace std;
 5 
 6 void function()
 7 {
 8     int step = 100000000;
 9     while (step--);
10 }
11 
12 int main()
13 {
14     //DWORD dwStart = GetTickCount();
15 
16     ULONGLONG dwStart = GetTickCount64();
17 
18     function();
19 
20     ULONGLONG dwEnd = GetTickCount64();
21     
22     auto cost = (dwEnd - dwStart);
23 
24     cout << "cost time : " << cost << endl;
25 
26     system("pause");
27 }
28 
29 /* result:
30 cost time : 157
31 请按任意键继续. . .
32 */

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：