[cfe-dev] Get underlying type of QualType if it's TypedefType

[陳韋任 via cfe-dev]

Kirill and Artem,

  My original approach is dyn_cast the type pointer to TypedefType
recursively since I need to take
nested typedef into consideration.

    typedef foo FOO;
    typedef FOO MyFoo;

    MyFoo b = (MyFoo)(a);

The recursive call is kinda of like,

    QualType getUnderlyingType(QualType QT) {

      if (const TypedefType *TT = dyn_cast<TypedefType>(QT)) {
          TypedefNameDef TND = TT->getDecl();
          return getUnderlyingType(TND->getUnderlyingType());
      }

      return QT;
    }

Both of you suggested *canonical* type, I tried and it works.

    QualType SrcCanonType = SrcExpr()->getType().getCanonicalType(),

    const BuiltinType *Src = SrcCanonType->getAs<BuiltinType>()

I guess getCanonicalType() way is preferred?

Regards,
chenwj


2017-04-13 5:51 GMT+08:00 Романенков Кирилл via cfe-dev <
cfe-dev at lists.llvm.org>:

> Hi,
>
> You can use getCanonicalType() to look through the typedefs, for example:
>
> QualType SrcCanonType = SrcExpr()->getType().getCanonicalType(),
>                 DestCanonType = DestType.getCanonicalType();
>
> if (const BuiltinType *Src = SrcCanonType->getAs<BuiltinType>())
>   if (const BuiltinType *Dest = DestCanonType->getAs<BuiltinType>()) {
>     if (Src.getKind() == Dest.getKind()) {
>       // do something
>     } else {
>       // do something else
>     }
> }
>
> Kirill
>
> > Date: Wed, 12 Apr 2017 23:11:29 +0800
> > From: 陳韋任 via cfe-dev <cfe-dev at lists.llvm.org>
> > To: cfe-dev at lists.llvm.org
> > Subject: [cfe-dev] Get underlying type of QualType if it's TypedefType
> > Message-ID:
> >         <CAFSLk9eRMBhHqLXR2WGWH7YLRgYe_eXNb0s8yXS6A=Y5MeTrZg at mail.
> gmail.com>
> > Content-Type: text/plain; charset="utf-8"
> >
> > Hi All,
> >
> >   I have SrcType and DestType used in explicit cast, and I'd like to
> check
> > if the type conversion is valid in CastOperation::CheckCStyleCast [1].
> The
> > code snippet below (just get the idea, the code is not runable),
> >
> >     Builtin *Src = dyn_cast<BuiltinType>(SrcExpr.get()->getType());
> >     Builtin *Dest = dyn_cast<BuiltinType>(DestType);
> >
> >     if (Src.getKind() == Dest.getKind()) {
> >       // do something
> >     } else {
> >       // do something else
> >     }
> >
> > The problem is the SrcType and DestType might be typedef. For example,
> >
> >     typedef foo FOO;
> >
> >     FOO b = (FOO)(a);
> >
> > Src and Dest might be nullptr due to the fail dyn_cast, and I will get
> > segfault while calling getKind() upon them.
> > I am not familiar with Clang, so is there a better way that I can get the
> > underlying type if SrcType and DestType
> > are typedef?
> >
> > Thanks.
> >
> > [1] https://clang.llvm.org/doxygen/SemaCast_8cpp_source.html
> >
> > Regards,
> > chenwj
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
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>



-- 

--
Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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