Re: Error C2555 with pointer to class with no template instantiation?

Ian Collins <>
Mon, 05 Mar 2007 18:50:39 +1300
<> wrote:

Error C2555

c:\C++ projects\stat1\stdmatrix_adapt.h(41) : error C2555:
'std_tools::Matrix_adapter<T>::at': overriding virtual function return
type differs and is not covariant from 'ple::imtx_impl<T>::at'

//in my program: the derived class
template <class T>
class Matrix_adapter : public ple::imtx_impl<T> {
    Matrix* m_;
    virtual const T& at(mtx_size i0, mtx_size i1) const //mtx_size -->
unsigned int
        {return m_->at(i0, i1);}
// the base class
template <class T>
class imtx_impl : public imtx<T> {
    virtual const T& at(mtx_size i0, mtx_size i1) const=0;

/*Notice returns a pointer to another class Matrix
The problem arises as this class Matrix has no template instantiation
and i set the virtual function at return as double, the same as T */

class Matrix : public GeneralMatrix
const double& at(unsigned int pos0, unsigned int pos1) const { return, pos1)); }

// However in my main program initiating T as double in the derived
class still gives the error C2555.

Matrix_adapter <double> matx;

Am at loss what to do now.. any people care to help... ?

The code fragments as posted look OK, can you reproduce the problem with
a self contained example?

Ian Collins.

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