Question

How to write copy constructor for a template class. So that if the template parameter is another user defined class it’s copy constructor is also get called.

Following is my class

template <typename _TyV>
class Vertex {
public:
    Vertex(_TyV in) :   m_Label(in){ }
    ~Vertex() { }
    bool operator < ( const Vertex & right) const {
        return m_Label < right.m_Label;
    }

    bool operator == ( const Vertex & right ) const {
        return m_Label == right.m_Label;
    }

    friend std::ostream& operator << (std::ostream& os, const Vertex& vertex) {
        return os << vertex.m_Label;    
    }

    _TyV getLabel() { return m_Label;}
private:
    _TyV m_Label;
public:
    VertexColor m_Color;
protected:
};

Answer 1

Assuming _TyV is a value type:

Vertex( Vertex const& src )
    : m_Label( src.m_Label )
{}

Aren’t those names within class instances reserved by the implementation, by the way?

The C++ standard reserves a set of names for use by C++ implementation and standard libraries [C++ standard 17.6.3.3 – Reserved names]. Those include but are not limited to:

• Names containing a double underscore.
• Names that begin with an underscore followed by an uppercase letter.
• Names that begin with an underscore at the global namespace.