adding to a set STL - C++

Question

I have a media program. i am adding CD,dvd,book info. I managed to get the book info added to the set. I am now adding the CD info. I have most of the Cd info added but i have a seperate function for adding band members. thats where i need help!

I am getting a cast error: error C2440: 'type cast' : cannot convert from 'const Item *const ' to 'CD'

CD.h

#ifndef CD_H
#define CD_H
#pragma once
#include "item.h"

class CD : public Item
{
public:

    CD(const string& theTitle, const string& theBand, const int snumber);
    const string addBandMember(const string& member);
    const int getNumber() const;
    const string getMusician() const;

    const string getBand() const;
    virtual void print(ostream& out) const;
    ~CD();


private:

    string band;
    string musicians;
    string title;
    int number;

};

ostream& operator<<(ostream& out, const CD* cd);

#endif

CD.cpp

const string CD::addBandMember(const string &member)
{

    return this->musicians = member;

}

Answer 1

In Library::addBandMember you're trying to cast a pointer to a class type
you need to cast to CD* not CD

And you probably don't want the 2 const in

const Item* const musicCD  

since you want to modify the musicCD !

finally your CD::addBandMember method doesn't seem to add a band member but replace it.

Answer 2

You need to change the signature of

void Library::addBandMember(const Item* const musicCD, const string& member)

to

void Library::addBandMember(const Item* musicCD, const string& member)

as addBandMember() method does indeed change your Item instance, so Item cannot be const. Then you need to cast it to CD* using dynamic_cast, because it is a downcast.