strcpy, strcmp, strlen, memcpy 实现

[cpp]
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

char *StrCpy(char *dest, const char *src)
{
     assert((dest != NULL) && (src != NULL));
     char *str = dest;
     while ((*dest ++ = *src ++) != '\0');
     return str;
}

int Strlen(const char *str)
{
     assert((str != NULL));
     int len = 0;
     while (*str ++)
     {
          len++;
     }
     return len;
}

int StrCmp(const char *str1, const char *str2)
{
     assert((str1 != NULL) && (str2 != NULL));
     int rt = 0;
     while ( !(rt = *(unsigned char *)str1 - *(unsigned char*)str2 ) && *str2)
     {
         str1 ++;
         str2 ++;
     }
     if (rt > 0)
     {
         rt = 1;
     }
     else if (rt < 0)
     {
         rt = -1;
     }
     return rt;
}

//为了解决内存重叠的现象
void *MemCpy(void *dst, const void *src, size_t count)
{
     char *pdst = static_cast<char *>(dst);
     const char *psrc = static_cast<const char *>(src);

     if (pdst > psrc && pdst < psrc + count)
     {
           for (int i = count - 1; i >= 0; i--)
           {
                pdst[i] = psrc[i];
           }
     }
     else
     {
           for (int i = 0; i < count; i++)
           {
                pdst[i] = psrc[i];
           }
     }
     return dst;
}

// memcpy 实现源码
void * __cdecl memcpy (
        void * dst,
        const void * src,
        size_t count
        )
{
        void * ret = dst;

        while (count--) {
                *(char *)dst = *(char *)src;
                dst = (char *)dst + 1;
                src = (char *)src + 1;
        }

        return(ret);
}

int main()
{
     char str2[100] = "abcd";
     char *str1 = (char *)malloc(100);
     str1= str2 + 2;
     //考虑了内存重叠
     MemCpy(str1, str2, 5);
     printf("调用MemCpy后str1的内容:     %s\n", str1);

     //未考虑内存重叠
     memcpy(str1, str2, 5);
     printf("调用memcpy后str1的内容:     %s\n", str1);
     while(1);
}

补充：软件开发 , C++ ,