The following C++ code compiles (but doesn't link) with g++ 4.3.1:
template <typename T_>
struct B
{
T_ f();
};
extern template class B<int>;
void f()
{
B<int> t;
t.f();
}
With 'gcc () 4.4.0-pre9999 built 20080827 (Gentoo SVN ebuild) rev. 139623', the
following error occurs:
$ g++ -O1 a.cc
a.cc: In instantiation of T_ B<T_>::f() [with T_ = int]:
a.cc:12: instantiated from here
a.cc:12: error: explicit instantiation of T_ B<T_>::f() [with T_ = int] but
no definition available
If no -O is specified, the error does not occur. Using -std=c++0x does not
alter the outcome.
I'm looking at n2723 14.7.2 for what the behaviour should be. My understanding
is as follows: By paragraph 7, the explicit instantiation declaration for
B<int> is also an explicit instantiation declaration for int B<int>::f(). Thus,
by paragraph 3, a definition of B<int> must be available when declaring int
B<int>::f(), which it is. But I don't see a requirement for a definition of
B<int>::f().
--
Summary: extern template / explicit instantiation broken in
4.4.0-pre
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ciaran dot mccreesh at googlemail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37256
