Hello all, why the codes below is wrong in g++ 3.4.2? an error occurs in the line: cout<<CMatrix<double>::eye(5); -------------------------------------- #include <ostream> #include <boost/numeric/ublas/matrix.hpp> #include <boost/numeric/ublas/io.hpp> using namespace boost::numeric::ublas; using namespace std; template <class T> class CMatrix { matrix<T>mat_; public: CMatrix(const identity_matrix<T>& m) { mat_ = m; } static CMatrix<T> eye(int size) { return identity_matrix<T>(size); } template <class T_> friend ostream& operator << (ostream& os, CMatrix<T_>& m); }; template<class T_> ostream& operator << (ostream& os, CMatrix<T_>& m) { os<<m.mat_; return os; } int main() { CMatrix<double>I = CMatrix<double>::eye(5); cout<<I; cout<<CMatrix<double>::eye(5);//this line ==> error } ---------------------------------------- Thanks in advance!