gwyn@smoke.BRL.MIL (Doug Gwyn) (11/09/89)
In article <15743@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael J Zehr) writes: >is this obfuscated code not ANSI or is the compiler broken? The compiler is broken.
henry@utzoo.uucp (Henry Spencer) (11/10/89)
In article <15743@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael J Zehr) writes: >is this obfuscated code not ANSI or is the compiler broken? It is legal, although ugly, ANSI C. Also legal (but ugly) traditional C. Dennis Ritchie himself has officially blessed this disgusting construct, and indeed it has one or two legitimate uses. -- A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
exspes@gdr.bath.ac.uk (P E Smee) (11/14/89)
In article <1989Nov9.200639.8868@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >In article <15743@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael J Zehr) writes: >>is this obfuscated code not ANSI or is the compiler broken? > >It is legal, although ugly, ANSI C. Also legal (but ugly) traditional C. >Dennis Ritchie himself has officially blessed this disgusting construct, >and indeed it has one or two legitimate uses. Can you point me at a reference in 'The C programming language' (or in any other reference that I'm likely to be able to find)? I'm *not* doubting you, but I *would* like to know exactly what it is supposed to mean, then. In particular, if you branch (via the switch) to one of the cases inside the {}'s of the for, are you then under control of the for? That is, do you iterate the for or do you fall out of the bottom bracket on the first go-through? -- Paul Smee | JANET: Smee@uk.ac.bristol Computer Centre | BITNET: Smee%uk.ac.bristol@ukacrl.bitnet University of Bristol | Internet: Smee%uk.ac.bristol@nsfnet-relay.ac.uk (Phone: +44 272 303132) | UUCP: ...!uunet!ukc!gdr.bath.ac.uk!exspes
peter@guardian.UUCP (peter) (11/15/89)
In article <1989Nov9.200639.8868@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: |In article <15743@bloom-beacon.MIT.EDU> tada@athena.mit.edu (Michael J Zehr) |writes: |>There was a recent article in comp.lang.c on obfuscated use of switches |>and labels mixed together which i decided to try to compile using DEC's |>VAX C (VMS) compiler: |>#include <stdio.h> |>main() { |> int i, j=1, k=1; |> for(i=0; i<=2; ++i) |> switch(i) { |> case 0: for(; ++k % 3; ++j) { |> case 1: printf(" j = %d,", j); |> case 2: printf(" k = %d,", k); |> } |> } |>} |> |>(i've reduced the code to just the section i have a question concerning) |> |>on the '1' and '2' case lines, the compiler gives an error "case labels |>are valid only in "switch" statements." |> |>is this obfuscated code not ANSI or is the compiler broken? | |It is legal, although ugly, ANSI C. Also legal (but ugly) traditional C. |Dennis Ritchie himself has officially blessed this disgusting construct, |and indeed it has one or two legitimate uses. (Michael Zehr's original posting added for clarity) I've stared at this and can't make sense of it. Could someone provide me with enlightenment? ------------------------------------------------------------------------------- Peter Plamondon, Intel Corp, 5200 NE Elam Young Pkwy, Hillsboro, OR 97124-6497 Internet: peter@langlab1.hf.intel.com +1 503-696-5219 UUNET : uunet!intelhf!langlab1!peter "I speak for myself, as best I can." UUCP : tektronix!psueea!foobar!langlab1.hf.intel.com!peter -------------------------------------------------------------------------------
henry@utzoo.uucp (Henry Spencer) (11/16/89)
In article <301@guardian.UUCP> peter@langlab1.hf.intel.com (Peter Plamondon) writes: >|> switch(i) { >|> case 0: for(; ++k % 3; ++j) { >|> case 1: printf(" j = %d,", j); >|> case 2: printf(" k = %d,", k); >|> } >|> } > >I've stared at this and can't make sense of it. Could someone provide me >with enlightenment? Rewrite it this way: if (i == 0) goto zero; else if (i == 1) goto one; else if (i == 2) goto two; else goto done; zero: for ... { one: printf...; two: printf...; } done: Yes, branching into a loop is disgusting, but it is legal. Don't ask me what the code is supposed to *do*. -- A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
gwyn@smoke.BRL.MIL (Doug Gwyn) (11/16/89)
In article <1989Nov14.104203.26192@gdt.bath.ac.uk> exspes@gdr.bath.ac.uk (P E Smee) writes: >In particular, if you branch (via the switch) to one of the cases >inside the {}'s of the for, are you then under control of the for? In C you may always branch to a label within a control construct such as the body of a "for" statement, whether or not a "switch" is involved. The associated semantics are fairly obvious if you grok the notions of labels, identifier scopes, and initialization of variables.