strcpy, strcmp, strlen, memcpy 实现

#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);}