RE: reverse of getchar() read() open() fopen() ?
I've never seen any such thing, but I've done similar things a lot. I'd say malloc/read the whole file in and use a decrementing pointer to return the previous character. -- Andrew Duane Juniper Networks 978-589-0551 10 Technology Park Dr adu...@juniper.net Westford, MA 01886-3418 From: owner-freebsd-hack...@freebsd.org [owner-freebsd-hack...@freebsd.org] On Behalf Of Julian H. Stacey [j...@berklix.com] Sent: Friday, February 11, 2011 4:32 PM To: hack...@freebsd.org Subject: reverse of getchar() read() open() fopen() ? Hi hackers@, Do we have C libraries with reverse of getchar() [ maybe read() ] fopen() [ maybe open() ] etc, to read from end of file toward beginning ? I dont see anything in the See Also sections. I'm not looking to write, just read. I'm looking for something that returns last char in file as first etc, I'm not interested in wchars etc, I could write some C functions, with seek etc probably will, if none exist, but no point if they already exist ? Cheers, Julian -- Julian Stacey, BSD Unix Linux C Sys Eng Consultants Munich http://berklix.com Mail plain text; Not quoted-printable, Not HTML, Not base 64. Reply below text sections not at top, to avoid breaking cumulative context. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: reverse of getchar() read() open() fopen() ?
In the last episode (Feb 11), Julian H. Stacey said: Hi hackers@, Do we have C libraries with reverse of getchar() [ maybe read() ] fopen() [ maybe open() ] etc, to read from end of file toward beginning ? I dont see anything in the See Also sections. I'm not looking to write, just read. I'm looking for something that returns last char in file as first etc, I'm not interested in wchars etc, I could write some C functions, with seek etc probably will, if none exist, but no point if they already exist ? tail -r does this on a line-by-line basis. Tail does it for regular files by mmaping and then reading backwards, but you could also read the block of data at (filesize MOD buffersize) and return its bytes in reverse order, then seek back buffersize bytes, read that block and print it reversed, etc. You might even be able to write functions that could be passed to funopen(). Then you'd have a regular FILE* that you could call with regular stdio functions. Getting the buffering right for good performance might get tricky, though. -- Dan Nelson dnel...@allantgroup.com ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: reverse of getchar() read() open() fopen() ?
On Fri, 2011-02-11 at 22:32 +0100, Julian H. Stacey wrote: Hi hackers@, Do we have C libraries with reverse of getchar() [ maybe read() ] fopen() [ maybe open() ] etc, to read from end of file toward beginning ? `tail -r' will spit out lines of a file in reverse-order. Maybe the source to tail(1) can offer some insights: http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.bin/tail/ -- Devin P.S. Sorry for the non-answer. I dont see anything in the See Also sections. I'm not looking to write, just read. I'm looking for something that returns last char in file as first etc, I'm not interested in wchars etc, I could write some C functions, with seek etc probably will, if none exist, but no point if they already exist ? Cheers, Julian ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: reverse of getchar() read() open() fopen() ?
Hi hackers@, Do we have C libraries with reverse of getchar() [ maybe read() ] fopen() [ maybe open() ] etc, to read from end of file toward beginning ? I dont see anything in the See Also sections. I'm not looking to write, just read. I'm looking for something that returns last char in file as first etc, I'm not interested in wchars etc, I could write some C functions, with seek etc probably will, if none exist, but no point if they already exist ? PS I'm not looking for a program that reverses chars in lines ( eg like my http://berklix.com/~jhs/src/bsd/jhs/bin/local/rev/ ), instead I'm wondering if we have functions that read binary backwards, \0 \n not special. Cheers, Julian -- Julian Stacey, BSD Unix Linux C Sys Eng Consultants Munich http://berklix.com Mail plain text; Not quoted-printable, Not HTML, Not base 64. Reply below text sections not at top, to avoid breaking cumulative context. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: reverse of getchar() read() open() fopen() ?
On Fri, Feb 11, 2011 at 10:32:46PM +0100, Julian H. Stacey wrote: Hi hackers@, Do we have C libraries with reverse of getchar() [ maybe read() ] fopen() [ maybe open() ] etc, to read from end of file toward beginning ? I dont see anything in the See Also sections. I'm not looking to write, just read. I'm looking for something that returns last char in file as first etc, I'm not interested in wchars etc, I could write some C functions, with seek etc probably will, if none exist, but no point if they already exist ? Use lseek() to position yourself, iterate over the file, copying into a small buffer, then iterate over your buffer in reverse? Maybe I misunderstood you... Cheers, Julian -- Brian Reichert reich...@numachi.com 55 Crystal Ave. #286 Derry NH 03038-1725 USA BSD admin/developer at large ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
Re: reverse of getchar() read() open() fopen() ?
Andrew Duane wrote: I've never seen any such thing, but I've done similar things a lot. I'd say malloc/read the whole file in and use a decrementing pointer to return the previous character. Thanks, but I'll need a loop too, as malloc(filesize()) would be too big, as I omitted to say I'll be running it from find, reading all files on system, including DVD images @ 4.7G. Some of my machines dont have that much swap, let alone RAM :-) Aside: I was doing inefficient things here with getchar() (while searching forward, for a one off run, (CPU cycles were cheaper than brain cycles, so it was easier to hack a pre-existing prog that used getchar() ). I was doing a search for (trailing) nulls blocks, from BSD tar silently zeroing data from bad media, per http://lists.freebsd.org/pipermail/freebsd-hackers/2011-January/034254.html http://www.freebsd.org/cgi/query-pr.cgi?pr=154407 http://berklix.com/~jhs/src/bsd/fixes/FreeBSD/src/gen/usr.bin/tar/ But my search logs from find with http://berklix.com/~jhs/src/bsd/jhs/bin/public/8f were too big, so I'll reduce by searching backward only indexing on trailing nulls. Dan Nelson wrote: You might even be able to write functions that could be passed to funopen(). Then you'd have a regular FILE* that you could call with regular stdio functions. Getting the buffering right for good performance might get tricky, though. Thanks, I didnt know funopen, I'll read it again tomorrow morning :-) Thanks to Devin Teske re src/usr.bin/tail/, sorry in my first post I forgot to say binary. Brian Reichert wrote: Use lseek() to position yourself, iterate over the file, copying into a small buffer, then iterate over your buffer in reverse? Yes, thanks, better for efficiency, being lazy I had first wondered if there was some fopen_starting_from_tail() getchar_starting_from_tail() I could just call for aone off run :-) Thanks all. Cheers, Julian -- Julian Stacey, BSD Unix Linux C Sys Eng Consultants Munich http://berklix.com Mail plain text; Not quoted-printable, Not HTML, Not base 64. Reply below text sections not at top, to avoid breaking cumulative context. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to freebsd-hackers-unsubscr...@freebsd.org
