refence to static class member from different dlls

[michael]

How can I reference an instance of a static class member accross all translation units? I don't want to pass a reference between dlls.
Lib1.dll

PROJECT 1
A.h
class A
{
public:
A();
~A();
static CString UserName; // static member

};

A.cpp
A:A() : Number(_T(""))
{ }
B.h

#include A.h
class B
{
public:
B();
~B();
void Login();
}

Extern CString _cdecspec(dllexport) A:UserName how do I export this static member ????????????????????????????????
B.cpp
CString A::UserName = "";

B::B() { }
B::Login()
{
A::UserName = "michael"; // this works good

}

------------------------------------------------------------------ translation units

Lib2.dll
PROJECT 2

C.h

#include A.h

class C ()
{
public:
C();
~C();
CString GetStaticUserName();
}

C.cpp
C::C()
{

}

CString C::GetStaticUserName()
{
return A:UserName;
}

error LNK2001: unresolved external symbol "public: static class ATL::CStringT<char,class StrTraitMFC_DLL<char,class ATL::ChTraitsCRT<char> > > CGlobals::UserName" (?gstrREFDB@CGlobals@@2V?$CStringT@DV?$StrTraitMFC _DLL@DV?$ChTraitsCRT@D@ATL@@@@@ATL@@A)