Re: Problem with line buffering and getc function on 1.7.33.

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Mar 12 20:39, Corinna Vinschen wrote:
> On Mar 11 16:05, Kaz Kylheku wrote:
> > We can reproduce the problem with just file streams using
> > a much simpler program:
> > 
> > #include <stdio.h>
> > 
> > int main(void)
> > {
> >   FILE *out = fopen("file", "w+");
> >   setvbuf(out, (char *) NULL, _IOLBF, 0);
> >   getc(out);
> >   clearerr(out);
> >   fseek(out, 0, SEEK_SET);
> >   putc('a', out);
> >   putc('b', out);
> >   putc('c', out);
> >   putc('d', out);
> >   putc('e', out);
> >   putc('\n', out);
> >   fclose(out);
> >   return 0;
> > }
> > 
> > The contents of file end up being "\n": one empty
> > line, instead of "abcde\n":
> > 
> >   $ cat file
> > 
> >   $
> 
> Thanks for the testcase.  I can reproduce the issue and I see where the
> problem occurs, but I'm still puzzled.  Comparing the code in our newlib
> C library with its BSD counterparts, I could swear the same behaviour
> happens on OpenBSD as well.  If not (which needs testing), I wonder why
> and where newlib's actually different.  Right now I don't see the
> difference.

I do now.  Basically it's setvbuf screwing up the internal flags in the
FILE structure.  I took the liberty to update newlib's setvbuf to the
OpenBSD version locally and I'm going to apply my patches to newlib
soon.  I'll provide a new 2.5.0 test release of Cygwin with this patch
tomorrow or early next week.


Thanks again for the testcase,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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