Messages in this thread |  | | Date | Wed, 21 Nov 2001 14:52:37 +0100 (CET) | From | Mathijs Mohlmann <> | Subject | Re: [BUG] Bad #define, nonportable C, missing {} |
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On 21-Nov-2001 Jan Hudec wrote: >> Go read up on C operator precedence. Unary ++ comes before %, so if we >> rewrite the #define to make it more "readable" it would be #define >> MODINC(x,y) (x = (x+1) % y) > > *NO* > MODINC(x,y) (x = (x+1) % y) > is correct and beaves as expected. Unfortunately: > MODINC(x,y) (x = x++ % y) > is a nonsence, because the evaluation is something like this > x++ returns x > x++ % y returns x % y > x is assigned the result and it's incremented IN UNDEFINED ORDER!!! > AFAIK the ANSI C spec explicitly undefines the order.
in fact, gcc does (according to my tests): MODINC(x,y) (x = (x % y) + 1)
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