一天一个CRT函数 memset

memset是我们coding的时候经常用到的内存操作函数，就是用来初始化结构体的数据。不过我还是推荐在C++中用构造函数的初始化列表来初始化，但对付C方式的struct还是memset吧，M$把这个CRT API实现得非常非常高效！

7.memset

1: /***

2: *Purpose:

3: *       把buffer所指内存区域的前uLen个字节设置成字符cVal

4: *

5: *Entry:

6: *       T *pDest - pointer to memory to fill with val

7: *       C val   - value to put in dst bytes

8: *       unsigned int uLen - number of bytes of dst to fill

9: *

10: *Exit:

11: *       returns pDest, with filled bytes

12: *

13: *Exceptions:

14: *

15: ***/

16: template<typename T, typename C>

17: inline T *tMemSet(T *pDest, C cVal, unsigned int uLen)

18: {

19:     while(uLen)

20:     {

21:         *pDest++ = cVal;

22:

23:         --uLen;

24:     }

25:

26:     return pDest;

27: }

很简单明了的实现，效率当然比不上用汇编写就的。还是简单测试下吧，看看到底差多少。

测试

1: volatile tChar buffer[] = _T("This is a test of the memset function This is a test of the memset function");

2:

3: volatile const DWORD dwCount = 10000000;

4:

5: DWORD dwLast = 0;

6: {

7:     CCYPerformance timer(dwLast);

8:     for(DWORD i = 0; i < dwCount; ++i)

9:     {

10:         CY_CRT::tMemSet(buffer, _T('*'), 40);

11:     }

12: }

13: cout << dwLast << endl;

14:

15: dwLast = 0;

16: {

17:     CCYPerformance timer(dwLast);

18:     for(DWORD i = 0; i < dwCount; ++i)

19:     {

20:         memset((void *)buffer, _T('*'), 40);

21:     }

22: }

23: cout << dwLast << endl;

结果：













呵呵，这就是差距~小样！！40多倍的差距。