Rule 19.4 Does "#define XY -1" violate 19.4

6.19 Preprocessing Directives

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[email protected]
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Rule 19.4 Does "#define XY -1" violate 19.4

Post by [email protected] » Thu Mar 17, 2016 3:37 pm

Dear MISRA Team,

as I found out, 2 out of 3 commercial MISRA checking tools report the statement "#define XY -1" to be a violation of rule 19.4. I am not sure whether or not this #define actually violates rule 19.4 but if so I would not fully understand the risk associated with this particular #define statement. Could someone please help and discuss if this is a violation and why it should be avoided?

Thank your for your support!

SimonB
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Joined: Fri Feb 05, 2016 3:04 pm
Company: General Dynamics

Re: Rule 19.4 Does "#define XY -1" violate 19.4

Post by SimonB » Fri Mar 18, 2016 11:58 am

I'm not surprised it's rejected. "-1" isn't an integer literal, it's the unary minus operator applied to a literal. This means that it's an expression and should be parenthesised.

I can't think of any cases where using it gives a surprisingly wrong answer, but it does allow things to compile that look wrong, such as:-

Code: Select all

	int b = 3 XY;
Simon

misra-c
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Re: Rule 19.4 Does "#define XY -1" violate 19.4

Post by misra-c » Fri Apr 08, 2016 8:42 am

The MISRA working group agree with the above response.
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Posted by and on behalf of
the MISRA C Working Group

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