Symbol resolution prevented by differences in class StrTrait? - c++

Question

In a new application, MyProg.exe, I would like to re-use a function defined in another dll/lib, MyDll.lib/.dll. The call has this signature:
CString CallToDllCodeFuncFromExe( const CString & someStr );
In MyProg.exe I #include the dll’s header file and input the MyDll.lib so the linker can resolve it, but I get an unresolved symbol.
MSDN tells me that one reason why this occurs may be that “A function is used but the type or number of the parameters do not match the function definition”. That seems to be the case here. Below is a comparison of the unmangled signatures for the function taken from the exe error messages and from a dumpbin of MyDll.lib. Notice that there is a difference in StrTraitMFC and StrTraitMFC_DLL which keeps it from resolving:
Build error message (unresolved symbols) of MyProg.exe:
__cdecl CallToDllCodeFuncFromExe(class ATL::CStringT< wchar_t,class StrTraitMFC< wchar_t,class ATL::ChTraitsCRT< wchar_t> > > const &)
Dumpbin /exports of MyDll.lib for CallToDllCodeFuncFromExe:
__cdecl CallToDllCodeFuncFromExe(class ATL::CStringT< wchar_t,class StrTraitMFC_DLL< wchar_t,class ATL::ChTraitsCRT< wchar_t> > > const &))
But in practice I notice that there is a workaround. All I need to do is template the function and the call works fine. Here is IntToStr with one token template parameter by value:
template< int N > CString IntToStr( int N )
{
CString intToStr;
intToStr.Format( L"%d", N );
return intToStr;
}
And the call is:
CString str = IntToStr< 33 >( 33 );
And the exported function looks like this:
class ATL::CStringT< wchar_t,class StrTraitMFC_DLL< wchar_t,class ATL::ChTraitsCRT< wchar_t> > > __cdecl IntToString(int)
My questions are, why does this workaround work and why doesn’t the non-templated call not work? Is it just a Visual Studio inconsistency/bug or is there something more C++ abstract going on here?