string系列之strcpy、strncpy、strcmp、strlen编程实现

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string系列

char* strcpy( char *strDest, const char *strSrc )
{
　assert((strDest != NULL) && (strSrc != NULL) );
char *address = strDest;
　while((*strDest++ = * strSrc++) != ‘\0’ );
return address;
}

char*strncpy(char* strdest, const char* strsrc, int n)
{
   assert((strdest != NULL) && (strsrc != NULL));
   char* address = strdest;
   while(n-- > 0)
      *strdest++ = *strsrc++;
   return address;
}

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

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