Unresolved Externals between functions

Question

I'm getting an unresolved external error but I can't figure out exactly what's causing it.

error LNK2019: unresolved external symbol "public: __thiscall ABC::ABC(class ABC const &)" (??0ABC@@QAE@ABV0@@Z) referenced in function "public: __thiscall hasDMA::hasDMA(class hasDMA const &)" (??0hasDMA@@QAE@ABV0@@Z)

1>C:\Users\Matt\documents\visual studio 2010\Projects\GSP_125_Lab5\Debug\GSP_125_Lab5.exe : fatal error LNK1120: 1 unresolved externals

The program runs when I delete this block of code:

hasDMA::hasDMA(const hasDMA & hs) : ABC(hs)
{
    style = new char[std::strlen(hs.style) + 1];
    std::strcpy(style, hs.style);
}

But I don't know what part of that is being referenced elsewhere.

Here is my ABC header and hasDMA header.

class ABC
{
private:
    enum {MAX = 35};
    char label[MAX];
    int rating;
protected:
    const char * Label() const {return label;}
    int Rating() const {return rating;}
public:
    ABC(const char * l = "null", int r = 0);
    ABC(const ABC & rs);
    virtual ~ABC() {};
    virtual ABC & operator*()  { return *this; }
    ABC & operator=(const ABC & rs);
    virtual void View() const = 0;
    friend std::ostream & operator<<(std::ostream & os, const ABC & rs);
};


class hasDMA :public ABC
{
private:
    char * style;
public:
    hasDMA(const char * s = "none", const char * l = "null",
              int r = 0);
    hasDMA(const char * s, const ABC & rs);
    hasDMA(const hasDMA & hs);
    ~hasDMA(){};
    hasDMA & operator=(const hasDMA & rs);
    virtual void View() const;
};

These are the only two ABC methods I have:

ABC::ABC(const char *l, int r)
{
    std::strcpy(label, l);
    label[MAX - 1] = '\0';
    rating = r;
}

ABC & ABC::operator=(const ABC & rs)
{
    if (this == &rs)
        return *this;

    strcpy(label, rs.label);

    return *this;
}

If it helps these are the rest of my hasDMA methods:

hasDMA::hasDMA(const char *s, const char *l, int r) : ABC (l, r)
{
    std::strcpy(style, s);
}

hasDMA::hasDMA(const char *s, const ABC & rs)
{
    std::strcpy(style, s);
}

void hasDMA::View() const
{
    cout << "Record Label: " << Label() << endl;
    cout << "Rating: " << Rating() << endl;
    cout << "Style: " << style << endl;

}

hasDMA & hasDMA::operator=(const hasDMA & hs)
{
    if (this == &hs)
        return *this;

    ABC::operator=(hs);
    style = new char[std::strlen(hs.style) +1];
    std::strcpy(style, hs.style);

    return *this;
}

Answer 1

You have declared an ABC copy constructor, but you haven't defined it.

ABC(const ABC & rs); // declaration. 

You will need to provide a definition, or remove the declaration.

You could greatly simplify the class by using an std::string instead of the char array. You wouldn't need to provide an assignment operator, copy constructor or destructor.

Answer 2

You forgot to define implementation for ABC(const ABC & rs);