Messages in this thread | | | Date | Tue, 01 Aug 2006 12:02:12 +0159 | From | Jiri Slaby <> | Subject | Re: do { } while (0) question |
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Peter Zijlstra wrote: > On Tue, 2006-08-01 at 11:45 +0159, Jiri Slaby wrote: >> Peter Zijlstra wrote: >>> On Tue, 2006-08-01 at 02:03 -0700, Hua Zhong wrote: >>>>> #if KILLER == 1 >>>>> #define MACRO >>>>> #else >>>>> #define MACRO do { } while (0) >>>>> #endif >>>>> >>>>> { >>>>> if (some_condition) >>>>> MACRO >>>>> >>>>> if_this_is_not_called_you_loose_your_data(); >>>>> } >>>>> >>>>> How do you want to define KILLER, 0 or 1? I personally choose 0. >>>> Really? Does it compile? >>> No, and that is the whole point. >>> >>> The empty 'do {} while (0)' makes the missing semicolon a syntax error. >> Bulls^WNope, it was a bad example (we don't want to break the compilation, just >> not want to emit a warn or an err). > > It was a perfectly good example why 'do {} while (0)' is useful. The > perhaps mistakenly forgotten ';' after MACRO will not stop your example > from compiling if KILLER == 1. Even worse, it will compile and do > something totally unexpected. > > If however you use KILLER != 1, the while(0) will require a ';' and this > example will fail to compile.
That's what I'm trying to say. It was a _bad_ piece of code. It doesn't demonstrate I want it to demonstrate.
> Not compiling when you made a coding error (forgetting ';' is one of the > most common) is a great help.
regards, -- <a href="http://www.fi.muni.cz/~xslaby/">Jiri Slaby</a> faculty of informatics, masaryk university, brno, cz e-mail: jirislaby gmail com, gpg pubkey fingerprint: B674 9967 0407 CE62 ACC8 22A0 32CC 55C3 39D4 7A7E - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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