OpenMP: VS2010 is configured to use OpenMP

A simple OpenMP example

       First start VisualStudio 2010 and create a new C++ console application, as shown below:

       Then select the project name on the project solution explorer, right-click, and select "Properties", as shown in the following figure:

       Then select "Configuration Properties" - "C/C++" - "Language" on the left side of the property page, and then select "Yes (/openmp)" after "OpenMP Support" on the right side, as shown in the following figure:

       Add the following code to the cpp file:

[cpp]  view plain copy  

1. #include "stdafx.h"  
2.   
3. #include<omp.h>  
4.   
5. #include<iostream>  
6.   
7. usingnamespace std;  
8.   
9.   
10. //loop test function  
11. void test()  
12. {  
13. for(int i=0;i<10000;i++)  
14. {  
15.   
16. }  
17. }  
18.   
19.   
20. int _tmain(int argc,_TCHAR* argv[])  
21. {  
22. cout<< "This is a serial test program!\n" ;  
23. double  start = omp_get_wtime( ); //Get the start time  
24.   
25. for(int i = 0; i < 10000; i++)  
26. {   
27. test();  
28. }  
29.   
30. double end = omp_get_wtime( );  
31.   
32. cout<<"计算耗时为："<<end -start<<"\n";  
33.   
34. cin>>end;  
35.   
36. return 0;  
37. }  

       以上代码中红色字体为添加的代码，以上程序是一个典型的串行程序，经过随机运行10次，其平均耗时约0.283273s（具体所耗时间跟测试计算机有密切的关系，测试电脑CPU采用Core I7 2630QM，4核）。

       下面将其转换成并行程序，只需要在for循环加上#pragma omp parallel for即可，如下代码（注意红色部分）：

[cpp]  view plain  copy

1. #include "stdafx.h"  
2.   
3. #include<omp.h>  
4.   
5. #include <iostream>  
6.   
7. using namespace std;  
8.   
9.   
10. //循环测试函数  
11. void test()  
12. {  
13. for(inti=0;i<10000;i++)  
14. {  
15.   
16. }  
17. }  
18.   
19. int _tmain(int argc, _TCHAR* argv[])  
20. {  
21. cout<<"这是一个并行测试程序!\n";  
22.   
23. doublestart = omp_get_wtime( ); //Get the start time  
24.   
25.   
26. #pragma ompparallel for  
27. for (inti = 0; i <10000; i ++)   
28. {  
29. test();  
30. }  
31.   
32.   
33. doubleend = omp_get_wtime( );  
34.   
35. cout<< "Calculation time is:" <<end -start<< "\n" ;  
36.   
37. cin>>end;  
38.   
39. return0;  
40. }  

       Similarly, after 10 random runs, the average time is about 0.06358044s. The comparison results of the two different running modes are shown in the following table:

frequency	serial	parallel
1	0.283382	0.0746704
2	0.283654	0.0686404
3	0.283212	0.0536631
4	0.280234	0.0517737
5	0.283041	0.0717588
6	0.283126	0.0524264
7	0.281881	0.0580316
8	0.283301	0.0730386
9	0.284545	0.0745088
10	0.286353	0.0572926
average value	0.283273	0.06358044

       The results of the two modes of operation are shown in the following figures:

       From the above analysis results, it can be seen that the time consumed by using OpenMP in parallel is only 22.44% of that in serial, which saves nearly 4.5 times the time.