Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!telxon!gorpong
From: gorpong@telxon.UUCP (Gordon C. Galligher)
Newsgroups: comp.lang.c
Subject: Re: Strange C Problem
Summary: printf() (normally) line buffers output
Keywords: Linked Lists
Message-ID: <43@telxon.UUCP>
Date: 10 May 89 17:55:30 GMT
References: <13812@paris.ics.uci.edu>
Distribution: na
Organization: Telxon Corporation, Akron Ohio
Lines: 60

In article <13812@paris.ics.uci.edu>, bvickers@bonnie.ics.uci.edu 
	(Brett J. Vickers) writes:
> 
[..much of example deleted..]
>   while (current != NULL) {
>     printf("%s\n",current->string);
>     printf("&");
[..rest of example deleted..]
> 
> ...strange happens.
> After the function has output its last message, it fails to continue
> on to the next line (printf("&")).  The ampersand isn't output until
> the next call to output_msgs().  

The subroutine printf() normally does its output to standard output, which on
most systems is considered a line-buffered output device.  This causes all
of the output sent to stdout to wait until it either gets a carriage return,
or if there is a request for input (the output is flushed before it waits for
input).  You can force the printing of the trailing ampersand in a few different
ways:

	1).  Change the printf from printf("&") to printf("&\n");  
		(Note this will cause an extra line feed each iteration through
		the while loop, if you do not want this, then use 2 or 3).

*	2).  Include fflush(stdout); either (i) directly after the printf() 
		(which causes it to be a wasted when more are pending) or
		(ii) put the fflush(stdout) after the WHILE loop exits and 
		before output_msg() returns.)
		(fflush(FILE *stream) is a subroutine call which flushes the
		buffer pointed at by 'stream'.  It will not cause a trailing
		new line, but will simply force the system to print out
		what is currently pending in the buffer.)

	3).  Include a putchar('\n'); after the while loop, which will put
		an extra newline after your '&' and before your next call to
		output_msg().

I would choose number '2' above because it doesn't cause any extra newlines
or carriage returns to show up in your output, but it does cause the trailing
'&' to be printed and then it will wait with it printed until you print out
any more stuff.  Because of the line-buffered nature of stdout, you will see
that you have a trailing '\n' in your first printf() line, which causes the
entire buffer to be flushed automatically.

> --
>  /*******************************************************************/
>  /*  "Eritis sicut Deus, scientes  *  bvickers@bonnie.ics.uci.edu   */
>  /*   bonum et malum"              *  ---------------------------   */
>  /*******************************************************************/

I hope this helps.

		-- Gordon.

-- 
Gordon C. Galligher  <|> ...!uunet!telxon!gorpong <|> gorpong@teleng.uucp.uu.net
Telxon Corporation   <|> "Captain, I hardly believe that insults are within your
Akron, Ohio, 44313   <|> prerogative as my commanding officer" - Spock
(216) 867-3700 (3512)<|>   (City on the Edge of Forever (Starring Joan Collins))