Re: "extern template class"

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 12 Jul 2009 08:36:35 -0400

Message-ID:

<#BWEn1uAKHA.2604@TK2MSFTNGP03.phx.gbl>

Igor R. wrote:

In MSVC 9.0 I try the following code:

//test1.h
template<class T> class Test1
{
public:
int func1();
};
extern template class Test1<int>;

//test1.cpp
#include "Test1.h"
template<class T>
int Test1<T>::func1()
{
return 1;
}
template class Test1<int>; //explicit instantiation

http://msdn.microsoft.com/en-us/library/by56e477.aspx

Both lines are explicit instantiations, and cannot coexist in the same
module. Just drop the line in the header with "extern" in it. The linker
will figure it all out.

"extern template" is only useful for importing template instantiations
from DLLs. See

http://support.microsoft.com/kb/168958

It talks about STL templates, but the same technique works for any other
template class.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925