[prev in list] [next in list] [prev in thread] [next in thread] 

List:       mingw-users
Subject:    Re: [Mingw-users] mingw-get with mintty; (was: old MSYS design gone)
From:       Andy Koppe <andy.koppe () gmail ! com>
Date:       2011-02-26 10:59:39
Message-ID: AANLkTikt_f2gZBNeRk9D=Q=He5Ce5GhOhbFvfwBukG7- () mail ! gmail ! com
[Download RAW message or body]

On 22 February 2011 17:03, Keith Marshall wrote:
> On 22 February 2011 15:14, Andy Koppe wrote:
> > On 22 February 2011 15:01, Keith Marshall wrote:
> > > On 22 February 2011 13:54, Albrecht Schlosser wrote:
> > > > Instead of using flush, it is also possible to set stdout and stderr
> > > > unbuffered unconditionally at program initialization:
> > > > 
> > > > setvbuf (stdout,NULL,_IONBF,0);
> > > > setvbuf (stderr,NULL,_IONBF,0);
> > 
> > _IOLBF ought to do the job too, except that according to MSDN "For
> > some systems, this provides line buffering. However, for Win32, the
> > behavior is the same as _IOFBF - Full Buffering." :(
> 
> So, yet another example of "broken windows" behaviour. :-)
> 
> AFAICT, the ISO C Standard insists that stderr shall *not* be fully
> buffered, when opened.  Ever.  (That is, irrespective of whether it is
> connected to a terminal or otherwise).  Thus, it might be unbuffered, or
> it might be line buffered, but it should never be fully buffered.  Okay,
> Windows apparently does not have any concept of line buffered (IOLBF)
> output, so that means, for standards conformance[*] stderr should never
> be anything other than unbuffered; yet it appears that it becomes fully
> buffered when connected to a pipe.

You're right. I wrote the little test below to check. It prints a row
of asterisks for each of the six combinations of stdin/stderr streams
and default/full/no buffering, with a small delay between each
asterisk. The asterisks should appear one-by-one when unbuffered and
all-at-once when buffered.

It shows that enabling and disabling buffering with setvbuf works
correctly both in the console and with a pty, i.e. a pipe. It also
confirms that on a pipe, both stdout and stderr are buffered by
deault. Finally, with a console, both stdout and stderr are unbuffered
by default.

Andy


#include <stdio.h>
#include <stdlib.h>

void test(FILE *f, char *s) {
  int i;
  fputs(s, f);
  fflush(f);
  for (i = 0; i < 60; i++) {
    fputc('*', f);
    usleep(10000);
  }
  fputc('\n', f);
  fflush(f);
}

int main(void) {
  test(stdout, "stdout default: ");
  test(stderr, "stderr default: ");
  setvbuf(stdout, 0, _IONBF, BUFSIZ);
  test(stdout, "stdout _IONBF:  ");
  setvbuf(stderr, 0, _IONBF, BUFSIZ);
  test(stderr, "stderr _IONBF:  ");
  setvbuf(stdout, 0, _IOFBF, BUFSIZ);
  test(stdout, "stdout _IOFBF:  ");
  setvbuf(stderr, 0, _IOFBF, BUFSIZ);
  test(stderr, "stderr _IOFBF:  ");
}

------------------------------------------------------------------------------
Free Software Download: Index, Search & Analyze Logs and other IT data in 
Real-Time with Splunk. Collect, index and harness all the fast moving IT data 
generated by your applications, servers and devices whether physical, virtual
or in the cloud. Deliver compliance at lower cost and gain new business 
insights. http://p.sf.net/sfu/splunk-dev2dev 
_______________________________________________
MinGW-users mailing list
MinGW-users@lists.sourceforge.net

This list observes the Etiquette found at 
http://www.mingw.org/Mailing_Lists.
We ask that you be polite and do the same.  Disregard for the list etiquette may \
cause your account to be moderated.

_______________________________________________
You may change your MinGW Account Options or unsubscribe at:
https://lists.sourceforge.net/lists/listinfo/mingw-users
Also: mailto:mingw-users-request@lists.sourceforge.net?subject=unsubscribe


[prev in list] [next in list] [prev in thread] [next in thread]