Re: Gnulib's freopen replacement and MinGW

> Date: Mon, 07 May 2012 06:44:00 -0600
> From: Eric Blake <[email protected]>
> CC: [email protected], [email protected]
> 
> >  FILE *
> >  rpl_freopen (const char *filename, const char *mode, FILE *stream)
> >  {
> >  #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
> > -  if (filename != NULL && strcmp (filename, "/dev/null") == 0)
> > +  if (filename == NULL)
> > +    {
> > +      if (strchr (mode, 'b'))
> > +	return _setmode (_fileno (stream), _O_BINARY) == -1 ? NULL : stream;
> > +      else
> > +	return _setmode (_fileno (stream), _O_TEXT) == -1 ? NULL : stream;
> 
> Shouldn't we be doing some sanity checking, as in ensuring that a
> read-only stream is not being reopened with 'w', or a write-only stream
> is not being reopened with 'r'?

It's desirable, but I don't know how to do that with MinGW.  There's
no F_GETFL or its equivalent, AFAIK (but I'd be glad to learn that I'm
wrong).

> Also, shouldn't we be honoring 'w' vs.
> 'a' and adjusting the underlying fd's O_APPEND bit accordingly?

Again, I don't know how to do that.  According to MSDN, _setmode
supports only O_BINARY and O_TEXT.  If the reality is different,
please tell.

(One thing that is missing in my patch is a call to fflush, since you
cannot switch modes in the middle of a buffered operation.)