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

• memcpy

   #include <stdio.h>
   #include <stdlib.h>
   #include <memory.h>
  
   void * mymemcpy(void* _Dst, void const* _Src, size_t _Size)
   {
       if (_Dst == NULL || _Src == NULL)
       {
           return NULL;
       }
  
       //转化成char类型,一次前进一个字节
       char *dst = _Dst;
       char *src = _Src;
  
       for (int i = ; i < _Size; i++)
       {
           dst[i] = src[i];
       }
  
       return _Dst;
   }
  
   void main()
   {
       int a[] = { ,,,,,,,,, };
       int *p = malloc(sizeof(int) * );
       int *tmp = mymemcpy(p, a, );
  
       for (int i = ; i < ; i++)
       {
           printf("%d\n" ,p[i]);
       }
  
       char str[] = "hello world";
       char mystr[];
       mymemcpy(mystr, str, strlen(str) + );
  
       printf("%s\n", mystr);
  
       system("pause");
   }

• memset

   void *mymemset(void *_Dst, int _Val, size_t _Size)
   {
       if (_Dst == NULL || _Val == NULL)
       {
           return;
       }
  
       for (int i = ; i < _Size; i++)
       {
           ((char *)_Dst)[i] = _Val;
       }
  
       return _Dst;
   }

• memmove

   void * mymemmove(void *_Dst, const void *_Src, size_t _Size)
   {
       if (_Dst == NULL || _Src == NULL)
       {
           return NULL;
       }
  
       void *psrc = malloc(_Size);//分配内存
       memcpy(psrc, _Src, _Size);
       memcpy(_Dst, psrc, _Size);
       free(psrc);
       return _Dst;
   }

• memicmp(比较指定字符串前n个字符串)

   int mymemicmp(const void *_Buf1, const void *_Buf2, size_t _Size)
   {
       //保存变量
       char *buf1 = _Buf1;
       char *buf2 = _Buf2;
  
       //结束标识
       char *end = buf1 + _Size;
  
       while ((*buf1 == *buf2) && buf1 != end)
       {
           buf1++;
           buf2++;
       }
  
       if (buf1 == end)
       {
           return ;
       }
       else
       {
           return *buf1 - *buf2 >  ?  : -;
       }
   }

• memchr(寻找一个字符串中是否有指定字符)

   void *mymemchr(void *start, char ch, int maxlength)
   {
       char *p = NULL;
       for (int i = ; i < maxlength; i++)
       {
           if (((char *)start)[i] == ch)
           {
               p = (char *)start + i;
               break;
           }
       }
       return p;
   }

• memccpy(复制n个字符,遇到指定值退出)

   void * mymemccpy(void * _Dst, const void *_Src, int _Val,size_t _MaxCount)
   {
       char *dst = _Dst;
       char *src = _Src;
  
       for (int i = ; i < _MaxCount; i++)
       {
           dst[i] = src[i];
           if (dst[i] == _Val)
           {
               break;
           }
       }
   }