macro definition in header file included in .c

[michele]

Hello,
First of all I would like to thank you for the great job you are doing with cppcheck: we are using it since year and it's a great tool.

I'm writing you because we often face an "information" when we have a macro defined in a header and we use it in a .c that includes that header: it seems like cppcheck it's not able to get the definition of the macro and it prints out "the value of 'MY_MACRO' is unknown".
I prepared a simple example I attached: the "information" I get is

Skipping configuration 'MY_MACRO' since the value of 'MY_MACRO' is unknown. Use -D if you want to check it. You can use -U to skip it explicitly.

I checked the forum and the manual but I cannot get how to get out of this error.
Best Regards
Michele

Michele Ing. Corradin
Group Technologic Development
Sicon Srl
tel. +39 (0)444 598803
e-mail : michele.corradin@socomec.com

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[versat]

I can confirm this behaviour.
Here is the output of analyzing the original a.c file and then analyzing b.c where the line with #error is commented out:

cppcheck --enable=all --debug "a.c"
Checking a.c ...
Checking a.c: MY_MACRO...
[a.c:16]: (information) Skipping configuration 'MY_MACRO' since the value of 'MY_MACRO' is unknown. Use -D if you want to check it. You can use -U to skip it explicitly.

cppcheck --enable=all --debug "b.c"
Checking b.c ...
[b.c:12]: (debug) valueflow.cpp:3134:valueFlowFunctionReturn bailout: function return; nontrivial function body

##file b.c

1:
|
11:
12: U32 fx ( )
13: {
14: U32 zVar@1 ;
15:
16: zVar@1 = $5 ;
17:
18: return 5 ;
19: }

##Value flow
Line 16
  5 always 5
Line 18
  5 always 5
[b.c:14]: (debug) Unknown type 'U32'.
[b.c:12]: (style) The function 'fx' is never used.

It seems like commenting out the line with #error and adding the line #define MY_MACRO 5 to a.c have similar effects.
These tickets might be (slightly) related:
https://trac.cppcheck.net/ticket/7917
https://trac.cppcheck.net/ticket/6672
https://trac.cppcheck.net/ticket/5112

For me it looks like a defect. Somehow the preprocessor code

#ifndef MY_MACRO
   #error "Define macro MY_MACRO"
#endif

might not be handled correctly when the definition of the macro is in a header.

[michele]

thanks for your verification and support
Michele

[versat]

I created the ticket https://trac.cppcheck.net/ticket/8404 in the issue tracker.