Re: fflush(NULL) clobbers input streams

[Ken Brown <kbrown@cornell.edu>]

On 7/18/2017 3:21 PM, Achim Gratz wrote:
> Corinna Vinschen writes:
>> Oh, and a plain C testcase, of course...
> 
> Call that fflush.c:
> 
> --8<---------------cut here---------------start------------->8---
> #include <stdio.h>
> int
> main(int argc, char **argv)
> {
>      char buf[1024];
>      int i;
>      char *bp = buf;
>      while (1) {
>          while ((i = getc(stdin)) != -1
>                 && (*bp++ = i) != '\n'
>                 && bp < &buf[1024])
>          /* DO NOTHING */ ;
>          *bp = '\0';
>          fprintf(stdout, "%s", buf);
>          fflush(NULL);
>          if (i == -1)
>              return 0;
>          bp = buf;
>      }
> }
> --8<---------------cut here---------------end--------------->8---
> 
> Then run:
> 
> gcc fflush.c -o fflush
> cat fflush.c | ./fflush 2>/dev/null > fflush.out
> diff fflush.c fflush.out
> 
> If things are working, fflush.c and fflush.out should be identical.
> Currently only the first line makes it into fflush.out on Cygwin.

I've checked that the 2017-03-08 snapshot is good and the 2017-03-10 
snapshot is bad.  I'll bisect further when I get a chance, but maybe 
that's already enough to pin down the problem.

Ken