Re: lnk2001 errors template function definition.

From:

"Tom Widmer [VC++ MVP]" <tom_usenet@hotmail.com>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 08 Nov 2007 17:43:12 +0000

Message-ID:

<#I#lW7iIIHA.4476@TK2MSFTNGP06.phx.gbl>

cablepuff@gmail.com wrote:

On Nov 5, 1:39 pm, "Doug Harrison [MVP]" <d...@mvps.org> wrote:

On Mon, 05 Nov 2007 19:39:46 -0000, "cablep...@gmail.com"

<cablep...@gmail.com> wrote:

Hi i have a function definition like this in the main file.
template <class T>
T randomfunc(const T& X, const T& N, const T& C)
{
return ((X*X)+C)%N;
}
When i invoke randomfunc<int>(5, 20, 6);
I get the error
primeMain.obj : error LNK2001: unresolved external symbol "class
BAAB::T __cdecl randomfunc(class BAAB::T const &,class BAAB::T const
&,class BAAB::T const &)" (?randomfunc@@YA?AVT@BAAB@@ABV1BAAB@@00@Z)
Whats the problem and how do i fix it?

It looks like some other file is using the template specialization
mentioned in the error message, but the linker can't find the object code
for it. This can happen if you've merely declared the template in whatever
file is using the specialization. In general, VC requires the template
definition to be visible everywhere the template is used, so move the
definition into an appropriate header file and #include it in every file
that uses the template.

--
Doug Harrison
Visual C++ MVP

hmm the thing is randomfunc is define in primeMain.cpp which gets
compile to primeMain.o

randomfunc is a function template, and therefore doesn't compile to
object code. Particular specializations may be compiled to object code,
but only if they are instantiated (in primeMain.cpp), either implicitly
or explicitly.

the file is being passed a boost::function parameter to some other
function.

In what file is the function passed? It had better be primeMain.cpp,
since that's the only file where it is legal to implicitly instantiate
randomfunc. Alternatively, you could explicitly instantiate the relevent
specialization of randomfunc in primeMain.cpp. Finally, you could move
the definition of randomfunc into primeMain.h

Tom