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From: "igodard at pacbell dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/52321] New: poor diagnostic of invalid cast
Date: Tue, 21 Feb 2012 01:36:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D52321

             Bug #: 52321
           Summary: poor diagnostic of invalid cast
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: igodard@pacbell.net


This code:
   class foo;
   class bar {};
   int main() {
       foo* f;
       bar* b =3D static_cast<bar*>(f);
       return 0;
       }

gets you this:

   s3:~/ootbc/sim$ g++ foo.cc
   foo.cc: In function =C3=A2int main()=C3=A2:
   foo.cc:5:30: error: invalid static_cast from type =C3=A2foo*=C3=A2 to ty=
pe =C3=A2bar*=C3=A2

The issued diagnostic is correct but not very helpful. The real bug is that
class foo is defined (somewhere else) as class foo : public bar {...}, but =
the
definitions wasn't imported. A diagnostic like:
   foo.cc: In function =C3=A2int main()=C3=A2:
   foo.cc:6:3: error: invalid use of incomplete type =C3=A2struct foo=C3=A2
   foo.cc:1:7: error: forward declaration of =C3=A2struct foo=C3=A2
(which is what you put out for -> on an undefined) would be *much* better.