How to write Template class copy constructor

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:
};

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.

Either a) not at all, just rely on the compiler-provided default; or b) by just invoking the copy constructor of the member:

template <typename T> struct Foo
{
  T var;
  Foo(const Foo & rhs) : var(rhs.var) { }
};

The point is of course that the compiler-provided default copy constructor does precisely the same thing: it invokes the copy constructor of each member one by one. So for a class that's composed of clever member objects, the default copy constructor should be the best possible.

Nawaz

template <typename T>
class Vertex {
public:

    //this is copy-constructor
    Vertex(const Vertex<T> &other) 
          : m_Color(other.m_Color),m_Label(other.m_Label)
    {
      //..
    }
    //..
};

But I don't think you need to explicitly define the copy-constructor, unless the class have pointer member data and you want to make deep-copy of the objects. If you don't have pointer member data, then the default copy-constructor generated by the compiler would be enough.

来源：https://stackoverflow.com/questions/7638296/how-to-write-template-class-copy-constructor

标签

c++

templates

copy-constructor