[Bug c++/52972] New: [4.6] Pure virtual method is called instead of child's method

[Bug c++/52972] New: [4.6] Pure virtual method is called instead of child's method

[drinob at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

             Bug #: 52972
           Summary: [4.6] Pure virtual method is called instead of child's
                    method
    Classification: Unclassified
           Product: gcc
           Version: 4.6.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: drinob@gmail.com


Created attachment 27150
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27150
Bug sample

drino@netbook:~/src$ g++ test.cpp
drino@netbook:~/src$ ./a.out 
pure virtual method called
terminate called without an active exception
Aborted

[Bug c++/52972] Pure virtual method is called instead of child's method

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-04-13 16:24:07 UTC ---
I think you are getting the correct behavior as the vtable for the base class
is the current vtable for this.

And "        return static_cast < Real* > (this);"  Does not change the vtable
of the return class.

[Bug c++/52972] Pure virtual method is called instead of child's method

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-04-13 16:27:44 UTC ---
right, during the base constructor the derived class hasn't been constructed
yet and you can't call its virtual functions

[Bug c++/52972] Pure virtual method is called instead of child's method

[drinob at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

--- Comment #3 from drinob at gmail dot com 2012-04-13 16:28:36 UTC ---
Yes, this is my mistake.

[Bug c++/52972] Pure virtual method is called instead of child's method

[drinob at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

--- Comment #4 from drinob at gmail dot com 2012-04-13 16:35:35 UTC ---
But it seems to work in g++ 4.3 (which is used at ideone.com):
http://ideone.com/zy5R4
Is that behavior uncorrect?

[Bug c++/52972] Pure virtual method is called instead of child's method

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-04-13 17:27:33 UTC ---
The standard says "Member functions can be called from a constructor (or
destructor) of an abstract class; the effect of making a virtual call to a pure
virtual function directly or indirectly for the object being created (or
destroyed) from such a constructor (or destructor) is undefined."

The program has undefined behaviour, there is no correct or incorrect behaviour
for the compiler. Whatever the compiler does with your program does is valid. 
Including setting fire to your computer.

[Bug c++/52972] Pure virtual method is called instead of child's method

[drinob at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52972

--- Comment #6 from drinob at gmail dot com 2012-04-13 17:43:44 UTC ---
Thank you for your explanation. Now it's all clear.