C++ "Virtual functions but no virtual destructors"

I have a base class Media and several derived classes, namely DVD, Book, etc... The base class is written as:

class Media{
    private:
        int id;
        string title;
        int year;
    public:
        Media(){ id = year = 0; title = ""; }
        Media(int _id, string _title, int _year): id(_id), title(_title), year(_year) {}
//      virtual ~Media() = 0;
        void changeID(int newID){ id = newID; }
        virtual void print(ostream &out);
};

The thing is: without the destructor, GCC gives me a bunch of warnings class has virtual functions but non-virtual destructor, but still compiles and my program works fine. Now I want to get rid of those annoying warnings so I satisfy the compiler by adding a virtual destructor, the result is: it doesn't compile, with the error:

undefined reference to `Media::~Media()`

Making the destructor pure virtual doesn't solve the problem. So what has gone wrong?

 

 

 

 

 

 

What you have commented out is a pure-virtual declaration for a destructor. That means the function must be overridden in a derived class to be able to instantiate an object of that class.

What you want is just a definition of the destructor as a virtual function:

virtual ~Media() {}

In C++ 11 or newer, it's generally preferable to define this as defaulted instead of using an empty body:

virtual ~Media() = default;

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edited Apr 30, 2021 at 16:14

 

answered Apr 5, 2012 at 8:05

 

Jerry Coffin

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ref : https://stackoverflow.com/questions/10024796/c-virtual-functions-but-no-virtual-destructors