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From: epsilon@wet.UUCP (Eric P. Scott)
Newsgroups: comp.sources.games.bugs,comp.sources.d,alt.sources.d
Subject: What setbuf() is and why you should use it
Summary: A few minutes of your time will save hours of mine
Keywords: curses fflush setbuf stdio
Message-ID: <283@wet.UUCP>
Date: 15 Jul 89 22:28:12 GMT
Reply-To: epsilon@wet.UUCP (Eric P. Scott)
Followup-To: comp.sources.games.bugs
Organization: Wetware Diversions, San Francisco
Lines: 39

Many, many screen-oriented applications posted to the net have a
serious flaw: they do terminal output a character at a time.
This is fine for single-user PCs running MSDOS.  This is NOT fine
for multi-user machines running UNIX.  The culprit here is
Standard I/O; stdout is not buffered when directed to a terminal.
(System V has line buffering, but it's not the appropriate
solution here.)  This means that a write(2) call is performed for
each character output.  This has substantial overhead on many
machines--not only does your program run slowly, response time
for everyone else is degraded.  The fix is very simple:
put
	setbuf(stdout, malloc(BUFSIZ));

early in main(), and (if you've done any output)

	fflush(stdout);

before asking for terminal input, sleeping, going heavily
compute-bound, changing tty modes, or using fork/exec/system-type
calls.  This causes stdio to store up to BUFSIZ (defined in
<stdio.h>) characters before demanding a context switch.  Since
BUFSIZ is typically 512 or 1024, this can be a substantial
improvement.

Make sure you have declared malloc to return the proper type for
your system (either char * or void *).

I urge source-group moderators to perform a cursory check before
redistributing submissions.  Note that the absence of setbuf/
setvbuf/setlinebuf calls does not automatically damn a program,
it just means that closer inspection is needed.  This issue comes
up often enough that it might warrant a mention in regular
monthly/quarterly postings.

					-=EPS=-

"We haven't found a cure for people who insist on writing
	printf("\n");
 but our efforts at rehabilitation have been largely successful."