Emacs doesn't show printf() output during debugging.

Emacs doesn't show printf() output during debugging.

[Lao JM]

When I debug my C program, I can't see the printf() output in any buffer.
However, I can provide input to scanf() in the GUD buffer. What should 
I do to show the output? I am using Emacs 21.3.50.1 (CVS) on Windows2000.

Thanks.

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Re: Emacs doesn't show printf() output during debugging.

[Eli Zaretskii]

> From: "Lao JM" <rolexletter@hotmail.com>
> Date: Wed, 17 Aug 2005 13:05:57 +0000
> 
> When I debug my C program, I can't see the printf() output in any buffer.
> However, I can provide input to scanf() in the GUD buffer. What should 
> I do to show the output? I am using Emacs 21.3.50.1 (CVS) on Windows2000.

What port of GDB is that?

Also, is it possible that your program doesn't fflush the standard
output after it calls printf?  I think redirecting stdout to a pipe
changes its buffering, so without fflush the characters may stay
buffered longer than with the console.

Re: Emacs doesn't show printf() output during debugging.

[Nick Roberts]

> When I debug my C program, I can't see the printf() output in any buffer.
> However, I can provide input to scanf() in the GUD buffer. What should 
> I do to show the output? I am using Emacs 21.3.50.1 (CVS) on Windows2000.

I don't debug on Windows but I have been told that this works:

;; If you are using Emacs and GDB on Windows you will need to flush the buffer
;; explicitly in your program if you want timely display of I/O in Emacs.
;; Alternatively you can make the output stream unbuffered, for example, by
;; using a macro:
;;
;;           #ifdef UNBUFFERED
;;	     setvbuf (stdout, (char *) NULL, _IONBF, 0);
;;	     #endif
;;
;; and compiling with -DUNBUFFERED while debugging.

I think that if the string to be printed is terminated with \n, this will
also display at the desired time (line buffering?).

Nick

Re: Emacs doesn't show printf() output during debugging.

[Rolex JM]

I have tried
       setvbuf (stdout, (char *) NULL, _IONBF, 0);
and
       fflush(stdout);
respectively. They both worked. Thanks lot.

>From: Nick Roberts <nickrob@snap.net.nz>
>To: Lao JM <rolexletter@hotmail.com>
>CC: help-gnu-emacs@gnu.org
>Subject: Re: Emacs doesn't show printf() output during debugging.
>Date: Thu, 18 Aug 2005 09:29:57 +1200
>
>
> > When I debug my C program, I can't see the printf() output in any 
buffer.
> > However, I can provide input to scanf() in the GUD buffer. What should
> > I do to show the output? I am using Emacs 21.3.50.1 (CVS) on 
Windows2000.
>
>I don't debug on Windows but I have been told that this works:
>
>;; If you are using Emacs and GDB on Windows you will need to flush the 
buffer
>;; explicitly in your program if you want timely display of I/O in Emacs.
>;; Alternatively you can make the output stream unbuffered, for example, 
by
>;; using a macro:
>;;
>;;           #ifdef UNBUFFERED
>;;	     setvbuf (stdout, (char *) NULL, _IONBF, 0);
>;;	     #endif
>;;
>;; and compiling with -DUNBUFFERED while debugging.
>
>I think that if the string to be printed is terminated with \n, this will
>also display at the desired time (line buffering?).
>
>Nick

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