Problem with static data members in templated class

From:

Andy <andyg1001@hotmail.co.uk>

Newsgroups:

comp.lang.c++

Date:

Mon, 4 Oct 2010 05:11:41 -0700 (PDT)

Message-ID:

<553d7fe5-093c-438e-90d8-afd2a7fa814f@n26g2000yqh.googlegroups.com>

Hi,

I have some code (below) that is giving me problems to compile. I'm
using
GCC 4.4, and have already posed this question on comp.gcc.help, but
am
trying here also in case someone here has had a similar problem and
knows
the solution.

The code is as follows:

template <char* T>
struct C1
  {
  C1() { }
/*C1(const C1& other) = delete;*/

  char operator()()
    { return *T; }
  };

struct C2
  {
  static char m;
  static C1<&m> op;
  };

template <typename T>
struct C3
  {
  static char m;
  static C1<&m> op1;
  static C1<&C2::m> op2;
  };

// Initialise C2::m and C2::op
char C2::m = 'a';
C1<&C2::m> C2::op;

// Initialise C3::m for type int
/** This line fails in Comeau C++ 4.3, but is ok in GCC 4.4 **/
template<> char C3<int>::m = 'b';

// Initialise C3::op2 for type int
template <typename T> C1<&C2::m> C3<T>::op2;
template C1<&C2::m> C3<int>::op2;

// Initialise C2::op1 for type int
#if 0
/** This doesn't compile in GCC 4.4 but does in Comeau C++ 4.3 **/
template <typename T> C1<&C3<T>::m> C3<T>::op1;
template C1<&C3<int>::m> C3<int>::op1;
#elif 0
/** This compiles, but doesn't link **/
template<>
C1<&C3<int>::m> C3<int>::op1;
#else
/** This compiles and links but requires the copy-constructor - bad!
**/
template<>
C1<&C3<int>::m> C3<int>::op1 = C1<&C3<int>::m>();
#endif

int main()
  {
  printf("%c\n", C2::op());
  printf("%c\n", C3<int>::op1());
  printf("%c\n", C3<int>::op2());
  return 0;
  }

The problem is in compiling the lines which deal with the
initialisation of
C3<int>::op1. The syntax that works (i.e. the third one) uses the
copy
constructor, but I really want to be able to disable the copy
constructor in
C1 in the final implementation. I should have thought that the first
syntax
should have worked, i.e.:

template <typename T> C1<&C3<T>::m> C3<T>::op1;
template C1<&C3<int>::m> C3<int>::op1;

but I get the error:

error: conflicting declaration 'C1<(& C3::m)> C3<T>::op1'
error: 'C3<T>::op1' has a previous declaration as 'C1<(& C3<T>::m)>
C3<T>::op1'
error: declaration of 'C1<(& C3<T>::m)> C3<T>::op1' outside of class
is not
definition

Syntax two compiles, but the linker fails with:

undefined reference to `C3<int>::op1'

Out of interest I tried the Comeau online test compiler, and it has
no
problem with the declaration of C3<int>::op1, but does have an error
with
the declaration of C3<int>::m!

I expect I'm missing a 'template' or 'typename' keyword somewhere
obvious.

If someone is able to help me out, I would be most grateful.

Thanks
Andy