• memcpy
  1 #include 
         
           2 #include 
          
            3 #include 
           
             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     else21     {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 }