Sender: nate AT cartsys DOT com
Message-ID: <3606DD51.AA4FB7E@cartsys.com>
Date: Mon, 21 Sep 1998 16:12:17 -0700
From: Nate Eldredge <nate AT cartsys DOT com>
MIME-Version: 1.0
To: Uhfgood <uhfgood AT aol DOT com>
CC: djgpp AT delorie DOT com
Subject: Re: Simple C question probably having to do with DJGPP
References: <19980920183653 DOT 24923 DOT 00002490 AT ng126 DOT aol DOT com>
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Uhfgood wrote:
> 
> Well here's is the simple question.  consider the following code :
> 
> printf("This demonstrates a \\a escape sequence: \a");
> getch();
> 
> Now answer me this, how come it waits until a key is pressed to display the
> string?
> 
> Now please I already know two ways to make it work like I think it's supposed
> to.
> one is to put a \n after the last part of the screen, and the other is to type
> "fflush(stdout);" but that still doesn't answer my basic question.  Please just
> explain it to me?  Also if you don't want to bother with this message after you
> read it just close it, instead of wasting your time writing me back a flame.
> (I'm not trying to be mean about, I just mean I figure it would take more
> effort to flame me than it would to either ignore the question, or tell me the
> answer)..

Firstly, did you read the FAQ?

The reason is buffering.  In DJGPP, file I/O requires a call to DOS,
which requires a switch to real mode.  All this is rather slow. 
Therefore, I/O is buffered, which means the library accumulates a larger
chunk of data before writing it, which decreases this overhead.

The `stdout' stream by default uses line buffering, which means the data
is not written until a newline character ('\n') is output.  This yields
a large performance advantage especially in cases where data is being
written one character at a time (with `putc', for instance).  Thus, when
you print a newline, the data is actually written to the device (the
console, in this case).

`fflush' is provided to get around this buffering; it has the effect of
immediately flushing the buffer of that stream and writing its data
immediately.

With `setvbuf', you can change the buffering parameters of streams.
-- 

Nate Eldredge
nate AT cartsys DOT com