void * memcpy(void * to, const void * from, size_t n)
{
  const char *c_from = from;
  char *c_to = to;
  while (n-- > 0)
    *c_to++ = *c_from++;
  return((void *) to);
}

----------
char * strcat0 (char* s, const char * d )
{
 char * to_s = s;

// while( *s++ !='\0' ); //也可
// s--;

 while( *s !='\0' )
  s++;
 
 while ( (*s++ = *d++ ) !='\0');

 return ( to_s );
}

----------
char * strcpy0 (char* s, const char * d )
{
 char * to_s = s;
  
 while ( (*s++ = *d++ ) !='\0');

 return ( to_s );
}