------- Comment #5 from reichelt at gcc dot gnu dot org 2005-11-29 20:33
-------
This is not a bug in GCC. The code is invalid.
Let's consider the following simplified example which is just a
part of the diamond:
A0
|
A
/
B
==========================
struct A0
{
A0(int);
};
struct A : virtual A0
{
A() : A0(0) {}
};
struct B : virtual A
{
B() : A() {}
};
==========================
[12.6.2]/6 of the standard states:
All sub-objects representing virtual base classes are initialized
by the constructor of the most derived class. If the constructor
of the most derived class does not specify a mem-initializer for a
virtual base class V, then V's default constructor is called to
initialize the virtual base class subobject. If V does not have an
accessible default constructor, the initialization is ill-formed.
A mem-initializer naming a virtual base class shall be ignored
during execution of the constructor of any class that is not the
most derived class.
The first sentence means that A *and* A0 are initialized by the
constructor of B. The second sentence says that V (which is A0 in
our case) is default constructed since B's constructor does not
specify a mem-initializer for V==A0. The next sentence says that
the example is ill-formed since V==A0 does not have an accessible
default constructor. That's why g++ gives the following diagnostic:
bug.cc: In constructor 'B::B()':
bug.cc:13: error: no matching function for call to 'A0::A0()'
bug.cc:3: note: candidates are: A0::A0(int)
bug.cc:2: note: A0::A0(const A0&)
The last sentence says that A0(0) is ignored in the constructor
of A when called by B (which makes sense, since A0 should be
constructed directly by B's constructor).
--
reichelt at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |reichelt at gcc dot gnu dot
| |org
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20207
