Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsfcgl!cca.ucsf.edu!wet!epsilon
From: epsilon@wet.UUCP (Eric P. Scott)
Newsgroups: comp.sources.games.bugs
Subject: Re: What setbuf() is and why you should use it
Keywords: curses fflush setbuf stdio
Message-ID: <295@wet.UUCP>
Date: 18 Jul 89 20:25:10 GMT
References: <283@wet.UUCP> <2245@auspex.auspex.com>
Reply-To: epsilon@wet.UUCP (Eric P. Scott)
Organization: Wetware Diversions, San Francisco
Lines: 45

In article <2245@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) writes:
>>The fix is very simple: put
>>	setbuf(stdout, malloc(BUFSIZ));
>>
>>early in main(),
>
>In which case, if you run out of e.g. swap space (or address space,
>unless you've got tons of it and haven't consumed it all due to some
>other bug), you may drop core.

I got a mail message claiming the same thing--on which system
does it occur?  All the ones I know of simply have malloc()
return a NULL pointer, which is valid input to setbu()--it sets
the stream unbuffered.

>[suggested checking malloc's return value]

In any case, if the first thing you do in a program is malloc()
and it fails, you're probably in serious trouble anyway.  (I
normally practice a fairly paranoid programming style, this being
one of the exceptions.)

Also, NULL should always be cast to a pointer of the desired type
when used explicitly.  I prefer  if (!(x))  to test for this
case; the ! operator is true against a NULL pointer type, \even
if/ your architecture uses something other than 0 to represent
NULL, and false otherwise.

>[suggested using a static buffer]

I've run across stdio implementations that are documented to only
work with buffers obtained from malloc().  (I presume this means
they free() on fclose, or somesuch nonsense.  There should be a
"MYBUF" flag, but since that isn't part of the documented
interface, some vendors didn't include it.

SunOS users: your stdio is different from all UNIX flavors I know
about.  See the setbuf(3s) manual page.  BSD users will probably
want to use the BSD-specific buffering functions as well.  It's a
lot easier to change a setbuf() to something "better" than to find
all the places to fflush if it's not done automatically as a side
effect of reading stdin.  I.e. plan for fully buffered terminal
output.

					-=EPS=-