Re: [Patch] Fix newlib/libc/stdio/fgetws.c issue

[Yvan ROUX <yvan dot roux at st dot com>]

Hi Corinna,

I wasn't aware of the mbsnrtowcs function existence, but it is indeed a far 
better solution.

Thanks
Yvan


On Wed, May 30, 2012 at 02:34:31PM +0200, Corinna Vinschen wrote:
> On May 30 13:22, Yvan ROUX wrote:
> > Hi,
> > 
> > The actual behaviour of the fgetws function doesn't match with its specs as it
> > doesn't read *at most* n-1 wide characters until a newline, but *every* wide
> > character until a newline or in buffers if no newline are found. This patch 
> > fixes this issue.
> 
> Thanks for the patch, but I think the bug in fgetws is a bit more
> convoluted.  The expressions:
> 
>   nl = memchr (fp->_p, '\n', fp->_r);
> 
> and
> 
>   nl != NULL ? (nl - fp->_p + 1) : fp->_r
> 
> determine the number of bytes to read from the input stream, but `n'
> determines the number of maximum wide chars to produce.  So using
> the result of the `nl' expressions to compute the number of wide chars
> is plain wrong.
> 
> So, what about this instead?  It uses the `nl' expressions to compute
> the maximum number of input bytes and n to determine the maximum number
> of wide chars in a call to mbsnrtowcs:
> 
> Index: libc/stdio/fgetws.c
> ===================================================================
> RCS file: /cvs/src/src/newlib/libc/stdio/fgetws.c,v
> retrieving revision 1.5
> diff -u -p -r1.5 fgetws.c
> --- libc/stdio/fgetws.c	30 May 2012 08:58:42 -0000	1.5
> +++ libc/stdio/fgetws.c	30 May 2012 12:33:08 -0000
> @@ -110,9 +110,13 @@ _DEFUN(_fgetws_r, (ptr, ws, n, fp),
>      {
>        src = (char *) fp->_p;
>        nl = memchr (fp->_p, '\n', fp->_r);
> -      nconv = _mbsrtowcs_r (ptr, wsp, &src,
> -			    nl != NULL ? (nl - fp->_p + 1) : fp->_r,
> -			    &fp->_mbstate);
> +      nconv = _mbsnrtowcs_r (ptr, wsp, &src,
> +			     /* Read all bytes up to the next NL, or up to the
> +				end of the buffer if there is no NL. */
> +			     nl != NULL ? (nl - fp->_p + 1) : fp->_r,
> +			     /* But never more than n - 1 wide chars. */
> +			     n - 1,
> +			     &fp->_mbstate);
>        if (nconv == (size_t) -1)
>  	/* Conversion error */
>  	goto error;
> 
> 
> Corinna
> 
> -- 
> Corinna Vinschen
> Cygwin Project Co-Leader
> Red Hat