garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) (10/09/89)
Original to: csgtkidd@medusa.ua.oz
This is a test message, but while I'm at it, just a small question:
Can anyone think of a tighter way of coding a filter to strip spaces
from the input stream than this?
main()
{
char ch;
for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1))
;
}
Thankew for any help...
gk
---
* Origin: Australian BBS Registry (Opus 3:680/808)cpcahil@virtech.UUCP (Conor P. Cahill) (10/16/89)
In article <16103@nswitgould.cs.uts.oz>, garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: > Can anyone think of a tighter way of coding a filter to strip spaces > from the input stream than this? > > main() > { > char ch; > > for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1)) > ; > } If by "tighter" you mean better performing the following would outdo yours by probably an order of magnitude: #include <stdio.h> main() { int ch; while( (ch=getchar()) != EOF) { if( ch != ' ' ) { putchar(ch); } } } Actually, my "order of magnitude" estimation is incorrect. Processing 90K of data using your program took 53 seconds of cpu time, while the example I gave took .4 seconds (more like 2 orders of magnitude). -- +-----------------------------------------------------------------------+ | Conor P. Cahill uunet!virtech!cpcahil 703-430-9247 ! | Virtual Technologies Inc., P. O. Box 876, Sterling, VA 22170 | +-----------------------------------------------------------------------+
johng@prism.cs.orst.edu (John A. Gregor) (10/16/89)
In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: >Can anyone think of a tighter way of coding a filter to strip spaces >from the input stream than this? > >main() >{ > char ch; > > for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1)) > ; >} Ick! Yuk! First, there are no awards for 'tight' source (small does not mean efficient). The killer is the 1 character reads and writes. There is this little problem with system calls, it's known as overhead. For each system call, your machine will have to do 2 context switches which are pretty expensive. Although it is more programmer work, what you should do is create two large buffers (one for reading and one for writing). Or you can use fread and fwrite, or getc and putc, which are also buffered. Lastly, do you have something against whitespace??? John Gregor johng@cs.orst.edu
gwyn@smoke.BRL.MIL (Doug Gwyn) (10/16/89)
In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: >Can anyone think of a tighter way of coding a filter to strip spaces >from the input stream than this? Actually, yes, but I don't want to encourage this utterly HORRIBLE program. Did you realize that unbuffered 1-byte reads/writes impose tremendous overhead? Or that many systems do not have UNIX-compatible read()/write() functions?
kremer@cs.odu.edu (Lloyd Kremer) (10/16/89)
In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: >Can anyone think of a tighter way of coding a filter to strip spaces >from the input stream than this? > >main() >{ > char ch; > > for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1)) > ; >} Others have mentioned the incredible overhead of 1-byte reads and writes, but there is another problem with this. On many systems, a write() of zero bytes sends EOF. The reading process may decide to exit after your first write() of zero bytes. The result would be to copy the input up to but not including the first space. -- Lloyd Kremer ...!uunet!xanth!kremer Have terminal...will hack!
diamond@csl.sony.co.jp (Norman Diamond) (10/17/89)
In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: >Can anyone think of a tighter way of coding a filter to strip spaces >from the input stream than this? > >main() >{ > char ch; > > for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1)) > ; >} Yeah! Strip the spaces from it!!!!!! (Oh by the way, a zillion calls to "getc" are faster than a zillion 1-byte calls to "read", and the same for half-a-zillion calls to "putc" although you'll have to move your (ch==' ')?0:xxxx test around in front of the "putc. But this doesn't make it tighter.) -- Norman Diamond, Sony Corp. (diamond%ws.sony.junet@uunet.uu.net seems to work) Should the preceding opinions be caught or | James Bond asked his killed, the sender will disavow all knowledge | ATT rep for a source of their activities or whereabouts. | licence to "kill".
karl@haddock.ima.isc.com (Karl Heuer) (10/17/89)
In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: >Can anyone think of a tighter way of coding a filter to strip spaces If tightness is of more concern than portabililty off UNIX, you could use main(){system("tr -d ' '");} which can be further improved by making it a shell script. Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint
dg@lakart.UUCP (David Goodenough) (10/17/89)
garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) sez: >Can anyone think of a tighter way of coding a filter to strip spaces >from the input stream than this? > >main() >{ > char ch; > > for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1)) > ; >} #include <stdio.h> main() { int ch; while ((ch = getchar()) != EOF) if (ch != ' ') putchar(ch); } However, contemplate what will happen to the correctness of either of the above programs if passed through such a filter. They will _BOTH_ break, either failing to compile or generating incorrect code if they do compile. -- dg@lakart.UUCP - David Goodenough +---+ IHS | +-+-+ ....... !harvard!xait!lakart!dg +-+-+ | AKA: dg%lakart.uucp@xait.xerox.com +---+
andre@targon.UUCP (andre) (10/18/89)
In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: >Can anyone think of a tighter way of coding a filter to strip spaces >from the input stream than this? >main() >{ > char ch; > > for(;read(0,&ch,1)==1;write(1,&ch,(ch==' ')?0:1)) > ; >} I'm going to be flamed for this but... main(c) { while(read(0,&c,1)>0&&(c-' '?write(1,&c,1):1)) ; } -- The mail| AAA DDDD It's not the kill, but the thrill of the chase. demon...| AA AAvv vvDD DD Ketchup is a vegetable. hits!.@&| AAAAAAAvv vvDD DD {nixbur|nixtor}!adalen.via --more--| AAA AAAvvvDDDDDD Andre van Dalen, uunet!hp4nl!targon!andre
condict@cs.vu.nl (Michael Condict) (10/19/89)
In article <647@targon.UUCP> andre@targon.UUCP (andre) writes: |In article <16103@nswitgould.cs.uts.oz> garth_kidd%680.808@fidogate.fido.oz (Garth Kidd) writes: |>Can anyone think of a tighter way of coding a filter to strip spaces |>from the input stream than this? | [ Horribly inefficient, unreadable program omitted ] |I'm going to be flamed for this but... | |main(c) |{ | while(read(0,&c,1)>0&&(c-' '?write(1,&c,1):1)) | ; |} And well you should be. All other considerations aside, your version won't work on machines where &c is the address of the most significant byte of c, rather than the least significant byte. On such machines you read each character into the most significant byte of c, then (c-' ') compares the least significant byte to ' '. Michael Condict Vrije University Amsterdam