[cfe-dev] Is it possible to avoid FP when there is #ifdef in the code

[Gábor Horváth via cfe-dev]

On 26 August 2015 at 17:04, Vedant Kumar via cfe-dev <cfe-dev at lists.llvm.org
> wrote:

> I don't think it's fair to call this a false positive, unless the "XYZ"
> macro is defined.
>
> The analyzer has to run the preprocessor to handle basic things like
> #include. Modifying the checker to do what you propose would require going
> from the AST -> source code, scanning for a preprocessor command, altering
> it, re-parsing it, re-running the checker etc.
>
> It would be easier to add a line like "(void) x;" to suppress the warning.
>

Other possible workarounds (in case you have several unused variables):
- You can use pragmas to disable some diagnostics for certain regions of
code.
- You can use compiler flags to disable some diagnostics for certain
translation units.
- You can always factor out platform dependent code to multiple files and
have the #ifdef on includes.

In general I do like that the compiler finds unused variables. Sometimes
this uncovers real bugs. Sometimes it just helps to maintain readable code.
IMHO it is better to have false positives than false negatives for this
warning.


>
> best
> vedant
>
> On Aug 26, 2015, at 1:35 AM, Daniel Marjamäki via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
> >
> > Hello!
> >
> > Sometimes there are false positives when #ifdef is used and for instance
> usage of some macro/parameter is hidden.
> >
> > I am running Clang in a project where we get several such FPs.
> >
> > Example code:
> >
> > void f(int x) {
> >    // ..code..
> > #ifdef XYZ
> >    dostuff(x);
> > #endif
> >    // ..code..
> > }
> >
> > Warning:
> > 1.c:1:12: warning: unused parameter 'x' [-Wunused-parameter]
> > void f(int x) {
> >           ^
> >
> >
> > Is there anything that can be done in the unused-parameter checker to
> prevent such FP?
> >
> > For instance.. is it possible to see if there was a #ifdef in a function
> and disable the warning in that function.
> >
> > Best regards,
> > Daniel Marjamäki
> >
> >
> >
> ..................................................................................................................
> > Daniel Marjamäki Senior Engineer
> > Evidente ES East AB  Warfvinges väg 34  SE-112 51 Stockholm  Sweden
> >
> > Mobile:                 +46 (0)709 12 42 62
> > E-mail:                 Daniel.Marjamaki at evidente.se
> >
> >
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