CODEWITHSUNDEEP
c++interfaceinstantiation
HoNgOuRu
HoNgOuRu

Reputation: 727

Cannot instantiate abstract class in C++ error

I want to implement an interface inside a "Dog" class, but I'm getting the following error. The final goal is to use a function that recieves a comparable object so it can compare the actual instance of the object to the one I'm passing by parameter, just like an equals. An Operator overload is not an option cause I have to implement that interface. The error triggers when creating the object using the "new" keyword.

" Error 2 error C2259: 'Dog' : cannot instantiate abstract class c:\users\fenix\documents\visual studio 2008\projects\interface-test\interface-test\interface-test.cpp 8 "

Here is the code of the classes involved:

#pragma once

class IComp
{
    public:
        virtual bool f(const IComp& ic)=0; //pure virtual function
};

    #include "IComp.h"
class Dog  : public IComp
{
    public:
        Dog(void);
        ~Dog(void);
        bool f(const Dog& d);
};

#include "StdAfx.h"
#include "Dog.h"

Dog::Dog(void)
{
}

Dog::~Dog(void)
{
}

bool Dog::f(const Dog &d)
{
    return true;
    }

#include "stdafx.h"
#include <iostream>
#include "Dog.h"

using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
    Dog *d = new Dog; //--------------ERROR HERE**

    system("pause");
        return 0;
}

Upvotes: 1

Views: 14530

Answers (3)

K-ballo
K-ballo

Reputation: 81349

    bool f(const Dog& d);

is not an implementation for IComp's

    virtual bool f(const IComp& ic)=0; //pure virtual function

Your definition of Dog's f is actually hidding the pure virtual function, instead of implementing it.

Upvotes: 1

Arnout Engelen
Arnout Engelen

Reputation: 6897

bool f(const Dog &d) is not an implementation of bool f(const IComp& ic), so the virtual bool f(const IComp& ic) still isn't implemented by Dog

Upvotes: 3

DeCaf
DeCaf

Reputation: 6096

Your class Dog does not implement the method f, because they have different signatures. It needs to be declared as: bool f(const IComp& d); also in the Dog class, since bool f(const Dog& d); is another method altogether.

Upvotes: 1

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