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> void operator << (ostream& os, CMatrix<T>& m)//////////// line A {} int main(){ CMatrix<double> I = CMatrix<double>::eye(5); cout<<I; cout<<CMatrix<double>::eye(5);//////////////// line B } ------------------------------------------- In the codes above, "line B" will causes an error in g++ 3.4.2: no match for 'operator<<' in 'std::cout << CMatrix<T>::eye(int) [with T = double]()' Arkadiy Vertleyb advised me to insert "const" in "line A". So, the new version of "line A" is: void operator << (ostream& os, const CMatrix<T>& m) OK, there's no error. But, why? "Arkadiy Vertleyb" <vertleyb@hotmail.com> ??????:eh0dec$ih5$1@sea.gmane.org...
"YYW" <yyw1_25@sohu.com> wrote
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)
Try this:
ostream& operator << (ostream& os, const CMatrix<T_>& m)
Regards, Arkadiy