Static const int attributes and template functions

Question

The following does not link with CC on Solaris9. From what I can glean from the standards committee's notes it looks like it should and it compiles and links fine with g++. If I use a cast in the function call: ("foo((int)B::X)") then it links. If I move the static initialization out of the class definition then it works as well. Should we expect this to work or not?
#include <iostream>
class B
public:
static const int X = 42;
template< typename T > void foo( const T& t ) { std::cout << t << std::endl;}
int main()
foo(B::X);
}

Answer 1

The C++ rule (C++ Standard, section 9.4.2 paragraph 4) is that a static const data member of integral type can have an in-class initializer, and the value can be used in integral constant expressions. But if the data member is used, it must be defined outside the class without an initializer. If gcc allows the code, it is by accident. Some other compilers (apart from Sun C++) do not.
Add the line
const int B::X;
somewhere at global scope (or at namespace scope if B is in a namespace) after the declaration of class B. But you can't put this definition in a header file. The entire program must have exactly one definition of the static member.