yystpcpy (char *yydest, const char *yysrc)
#else
static char *
yystpcpy (yydest, yysrc)
    char *yydest;
    const char *yysrc;
#endif
{
  char *yyd = yydest;
  const char *yys = yysrc;

  while ((*yyd++ = *yys++) != '\0')
    continue;

  return yyd - 1;
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.