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Re: Interesting preprocessor code behavior

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Re: Interesting preprocessor code behavior

Subject: Re: Interesting preprocessor code behavior
From: Bill Royds <email@hidden>
Date: Thu, 3 Jul 2008 13:57:02 -0400


On 3-Jul-08, at 11:55 , Howard Moon wrote:

Preprocessor comparisons (like #if (A==B)) cannot be relied upon to consistently pass OR fail if either symbol is undefined.

An undefined symbol has the value 0 when evaluated, so if A is undefined, this expression depends on the value of B. It will NOT evaluate to false consistently, but to the value of #if (0 ==B) which evaluates to true if B is defined and equal to 0 or B is undefined as well.

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  >Interesting preprocessor code behavior (From: Howard Moon <email@hidden>)




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