Date:           Mon, 27 Feb 95  13:58 GMT
From: "Kevin Ashley, Systems Development, ULCC" <CZIWKGA AT VMSFE DOT ULCC DOT AC DOT UK>
To: JKEENE%EDU DOT UNL DOT UNLINFO AT GENERAL DOT ULCC DOT AC DOT UK,
        DJGPP%SUN DOT SOE DOT CLARKSON DOT EDU AT GENERAL DOT ULCC DOT AC DOT UK
Subject:        RE: Question reagarding kbhit()

From: 
Message-Id: <9502270633 DOT AA23500 AT unlinfo DOT unl DOT edu>
Subject: Question reagarding kbhit()
To: djgpp AT edu DOT clarkson DOT soe DOT sun
Date: Mon, 27 Feb 1995 00:33:38 -0600 (CST)
X-Mailer: ELM [version 2.4 PL20]
Content-Type: text
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Sender: djgpp-bounces AT edu DOT clarkson DOT soe DOT sun

jkeene AT edu DOT unl DOT unlinfo (Jon Keene) , who signs himself Rumball,
asks:
>
>Could anyone tell me why it is that when I run the following
>program, it pauses for the keyboard hit _before_ doing any output?
>

Short answer: yes.

Longer: Because stdout is line-buffered by default and you haven't flushed
        its buffer. The STDIO libraries save wear and tear on system calls
        by buffering data in various ways. Streams are either unbuffered
        (every call causes an immediate write()) line-buffered (write() only
        gets called when a newline is output) or block-buffered (only do
        a write() when N blocks of data have been output.) stdout is usually
        line-buffered and stderr is unbuffered. You can force buffers to be
        written when they wouldn't by using fflush(stream). The STDIO library
        does this automatically so far as I recall in the special case where
        you are about to read from stdin ; it flushes stdout. This is on the
        assumption that they both usually point at your
        terminal/screen/keyboard.

        kbhit() has nothing to do with the stdio library and works at a lower,
        bit-twiddlier level. Use fflush(stdout) before the while(!kbhit())
        loop, or change stdout to be unbuffered. If you're doing lots of
        putc(), the latter is a bad idea.

------------------------------------------------------------------------------
Kevin Ashley                              K DOT Ashley AT Ulcc DOT ac DOT uk
Systems Development Group Manager      http://www.ulcc.ac.uk/staff/Kevin+Ashley
University of London Computer Centre.      ...ukc!ncdlab!K.Ashley
           Founder inductee in the WWW Useless Page Hall of Fame
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