Casting pointer as template argument: Comeau & MSVC compile, GCC fails

Question

Consider the following code:

template<int* a>
class base {};

int main()
{
    base<(int*)0> test;
    return 0;
}

Both Comeau and MSVC compile this without issues (except for Comeau warning about an unused variable), while GCC fails on the base<(int*)0> test; line, stating

In function `int main()': a casts to a type other than an integral or enumeration type cannot appear in a constant-expression

template argument 1 is invalid

What exactly is it complaining about? And who's right -- should this code compile? It's worth noting that my GCC version is extremely old (3.4.2) so that may have something to do with it. Thanks.

Answer 1

From a draft standard (emphasis added):

14.1.3 A non-type template-parameter shall have one of the following (option-
  ally cv-qualified) types:
  ...
  --pointer to object, accepting an address constant  expression  desig-
    nating a named object with external linkage,
  ...

Apparently, it's not legal to instantiate a template with a null pointer, as a null pointer doesn't point to a "named object with external linkage".