another c++ q (with specialization and inheritance )

[Erez D]

i am having problems compiling the following code:
====================================

#if 1
template <class T> class c1 {};
template <class T> class c2 : public c1<T> { public: c2(T &a); };
#else
template <class T> class c1;
template <class T> class c2;
#endif

template <> class c1<int>
{
        int m_a;
        public:
        c1():m_a(0) {};
        c1(int a):m_a(a) {};
        c1(int &a):m_a(a) {};
        void set(const int a) {m_a=a;};
        const int get(void) const {return m_a;};
        c2<int> gen_c2(int a)
        {
                c2<int> ret(a);
                return ret;
        }
        const c1<int> &operator=(const c1<int> &other) {set(other.get());
return *this;};
};

template <> class c2<int> : public c1<int>
{
public:
        c2(int &a):c1(a) {};
};

int main()
{
        c1<int> a;
        c2<int> b=a.gen_c2();
}
===========================================
if i compile it, i get:
file.cpp:27: error: specialization of ‘c2<int>’ after instantiation

if on the other hand i change the #if 1 to #if 0, i get:
file.cpp: In member function ‘c2<int> c1<int>::gen_c2(int)’:
file.cpp:20: error: return type ‘struct c2<int>’ is incomplete
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