Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!mcnc!gatech!hao!oddjob!gargoyle!ihnp4!homxb!mhuxt!mhuxm!mhuxo!ulysses!sfmag!sfsup!mpl From: mpl@sfsup.UUCP (M.P.Lindner) Newsgroups: comp.os.minix Subject: Re: Keeping exit(3) small but making it work for stdio -- atexit() Message-ID: <1607@sfsup.UUCP> Date: Thu, 9-Jul-87 20:47:14 EDT Article-I.D.: sfsup.1607 Posted: Thu Jul 9 20:47:14 1987 Date-Received: Sun, 12-Jul-87 09:23:47 EDT References: <3118@felix.UUCP> <2352@hoptoad.uucp> <3169@felix.UUCP> <333@mcdsun.UUCP> Organization: AT&T-IS, Summit N.J. USA Lines: 66 Summary: data.c In article <333@mcdsun.UUCP>, fnf@mcdsun.UUCP writes: < In article <2368@hoptoad.uucp> gnu@hoptoad.uucp (John Gilmore) writes: < >While Art's solution works, there is a cleaner solution than [text deleted] < function, just set a global pointer (_stdio_cleanup) in exit and insure < that it got dereferenced *after* all the functions registered by atexit(). < < P.S. I put my pointer initialization as the first statement in flsbuf() < in flsbuf.c: < < unsigned char c1; < + extern VOID (*_stdio_cleanup)(); /* Found in exit() module */ < < + _stdio_cleanup = _cleanup; [more text deleted] < This may or may not be the theoretically correct place to put it, so if < someone more knowledgeable about stdio wants to speak up... [still MORE text deleted] < = Fred Fish Motorola Computer Division, 3013 S 52nd St, Tempe, Az 85282 USA > = seismo!noao!mcdsun!fnf (602) 438-5976 The correct thing to do theoretically is declare _stdio_cleanup to be a global in exit, and declare *and initialize* it in data.c (the file which declares _iob). That way, if there's no reference to stdio, data.c doesn't get loaded becasue there's no unresolved reference to _stdio_cleanup. However, if any stdio is used, data.c will get loaded (since _iob is referenced), and the loader will merge the two declarations (technically non-kosher, but laoders do these things) producing the desired result. As an exampl (and also a test) try the following: main.c: main() { foo(); } foo.c: int foobar; foo() { printf("%d\n", foobar); } bar.c: int xyzzy; int foobar = 3; cc -c foo.c bar.c ar rv libbar foo.o bar.o cc main.c libbar a.out should print "0" for the value of foobar as printed by foo(). now edit main.c: extern int xyzzy; main() { xyzzy = 0; foo(); } cc main.c libbar a.out should print "3" for the value of foobar, since the reference to xyzzy pulled in bar.o which initialized foobar to 3. Simple, no? The method of putting the statement in flsbuf has the disadvantage that if flsbuf is never called (ie no output buffer is filled by the program), the output doesn't get flushed. Thus, a program like printf("hello world") fails to produce output, while printf("hello world\n") works, because of line buffering. I hope I was able to explain this satisfactorily to the net audience. Mike Lindner ....!ihnp4!attunix!mpl