Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!cornell!uw-beaver!teknowledge-vaxc!sri-unix!quintus!ok From: ok@quintus.uucp (Richard A. O'Keefe) Newsgroups: comp.unix.wizards Subject: Re: setlinebuf(stdin) Keywords: open(2), close(2), exit(2) Message-ID: <294@quintus.UUCP> Date: 14 Aug 88 21:17:16 GMT References: <1122@ssc-bee.ssc-vax.UUCP> <291@quintus.UUCP> <12994@mimsy.UUCP> Sender: news@quintus.UUCP Reply-To: ok@quintus.UUCP (Richard A. O'Keefe) Organization: Quintus Computer Systems, Inc. Lines: 29 In article <12994@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes: >In article <291@quintus.UUCP> ok@quintus.uucp (Richard A. O'Keefe) writes: >>The remedy is simple. Only your program needs to change. >>Before reading from stdin, do >> setbuf(stdin, (char*)NULL); /* all flavours */ >>or setlinebuf(stdin); /* BSD */ >>or use setvbuf in System V. > >Setlinebuf() has no effect on input streams. I imagine setvbuf will >not set line-at-a-time reading on SysV either. Think about it: how >will you tell the system to read only up through a newline? Obviously, you can't. Just as obviously, if you are reading from a device which can seek, after reading the line you could seek back to the end of the line. Or you could simulate line buffering by doing character buffering. I made a classic mistake: I assumed stdio was smart and, mea culpa, tested one method and suggested an additional one I hadn't tested. Stupid, stupid! >Using setbuf(stdin, (char *)NULL) will do the trick, but is terribly >inefficient. I prefer my fseek-before-exit suggestion . . . . The snag with that (which is what I *thought* setlinebuf did on input, silly me) is that it won't work on pipes. setbuf(stdin, (char*)NULL) _will_ work on pipes, and we're only talking about reading a couple of dozen characters, so the overhead is small compared with the overhead of starting up a new process instead of using $< .