41.内存函数实现(memcpy,memset,memmove,memicmp,memchr.memccpy)

  • memcpy 
     1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <memory.h>
 4 
 5 void * mymemcpy(void* _Dst, void const* _Src, size_t _Size)
 6 {
 7     if (_Dst == NULL || _Src == NULL)
 8     {
 9         return NULL;
10     }
11     
12     //转化成char类型,一次前进一个字节
13     char *dst = _Dst;
14     char *src = _Src;
15 
16     for (int i = 0; i < _Size; i++)
17     {
18         dst[i] = src[i];
19     }
20 
21     return _Dst;
22 }
23 
24 void main()
25 {
26     int a[10] = { 1,2,3,4,5,6,7,8,9,10 };
27     int *p = malloc(sizeof(int) * 10);
28     int *tmp = mymemcpy(p, a, 40);
29 
30     for (int i = 0; i < 10; i++)
31     {
32         printf("%d\n" ,p[i]);
33     }
34 
35     char str[100] = "hello world";
36     char mystr[100];
37     mymemcpy(mystr, str, strlen(str) + 1);
38 
39     printf("%s\n", mystr);
40 
41     system("pause");
42 }

     

  • memset 
     1 void *mymemset(void *_Dst, int _Val, size_t _Size)
 2 {
 3     if (_Dst == NULL || _Val == NULL)
 4     {
 5         return;
 6     }
 7 
 8     for (int i = 0; i < _Size; i++)
 9     {
10         ((char *)_Dst)[i] = _Val;
11     }
12 
13     return _Dst;
14 }

     

  • memmove 
     1 void * mymemmove(void *_Dst, const void *_Src, size_t _Size)
 2 {
 3     if (_Dst == NULL || _Src == NULL)
 4     {
 5         return NULL;
 6     }
 7 
 8     void *psrc = malloc(_Size);//分配内存
 9     memcpy(psrc, _Src, _Size);
10     memcpy(_Dst, psrc, _Size);
11     free(psrc);
12     return _Dst;
13 }

     

  • memicmp(比较指定字符串前n个字符串) 
     1 int mymemicmp(const void *_Buf1, const void *_Buf2, size_t _Size)
 2 {
 3     //保存变量
 4     char *buf1 = _Buf1;
 5     char *buf2 = _Buf2;
 6 
 7     //结束标识
 8     char *end = buf1 + _Size;
 9 
10     while ((*buf1 == *buf2) && buf1 != end)
11     {
12         buf1++;
13         buf2++;
14     }
15 
16     if (buf1 == end)
17     {
18         return 0;
19     }
20     else
21     {
22         return *buf1 - *buf2 > 0 ? 1 : -1;
23     }
24 }

     

  • memchr(寻找一个字符串中是否有指定字符) 
     1 void *mymemchr(void *start, char ch, int maxlength)
 2 {
 3     char *p = NULL;
 4     for (int i = 0; i < maxlength; i++)
 5     {
 6         if (((char *)start)[i] == ch)
 7         {
 8             p = (char *)start + i;
 9             break;
10         }
11     }
12     return p;
13 }

     

  • memccpy(复制n个字符,遇到指定值退出) 
     1 void * mymemccpy(void * _Dst, const void *_Src, int _Val,size_t _MaxCount)
 2 {
 3     char *dst = _Dst;
 4     char *src = _Src;
 5 
 6     for (int i = 0; i < _MaxCount; i++)
 7     {
 8         dst[i] = src[i];
 9         if (dst[i] == _Val)
10         {
11             break;
12         }
13     }
14 }

     

posted @ 2018-01-25 16:58  喵小喵~  阅读(349)  评论(0)  编辑  收藏  举报