hierarchy of abstract interfaces implementation

Hello,

I have a hierarchy of abstract interfaces to be used by an other api. For exemple:
//*******************
#include <iostream>
using namespace std;

class AnimalInterface
{
public:
virtual ~AnimalInterface() = 0;
virtual void eat () = 0;
};

AnimalInterface::~AnimalInterface()
{}

class BirdInterface : public AnimalInterface
{
public:
virtual ~BirdInterface() = 0;
virtual void fly() = 0;
};

BirdInterface::~BirdInterface()
{
}

class Animal : public AnimalInterface
{
public:
void eat () { cout << "miam miam..." << endl;};
};

class Bird : public BirdInterface, public Animal
{
public:
void fly() { cout << "flap flap flap ..." << endl;};
void eat () { Animal::eat(); } ;
};

int main(int argc, char **argv) {
Bird bird;
bird.eat();
bird.fly();
}
//*******************

I have a problem with the method Bird::eat, it requires to explicitly calls the ancestor Animal::eat method. It becomes complicated to recall the ancestor methods for descendent classes when the hierarchy increases in size.
Do you know a way to avoid this kind of repetitions or something that would mean the class Bird implements the AnimalInterface through the Animal class.

Instead of trying to cram many methods into a single interface, consider separating them according, as per the interface segregation principle. Maybe you could have something like this:

Code:

---

#include <iostream>

using namespace std;

class EaterInterface
{
public:
    virtual void eat() = 0;
    virtual ~EaterInterface() = default;
};

class FlyerInterface
{
public:
    virtual void fly() = 0;
    virtual ~FlyerInterface() = default;
};

class Animal : public EaterInterface
{
public:
    void eat() override {
        cout << "miam miam..." << endl;
    }

    virtual ~Animal() = 0;
};

Animal::~Animal() {}

class Bird : public Animal, public FlyerInterface
{
public:
    void fly() override {
        cout << "flap flap flap ..." << endl;
    }
};

int main() {
    auto bird = Bird{};
    bird.eat();
    bird.fly();
}

---

When posting code, please use code tags. Go Advanced, select the formatted code and click '#'.

Your design also has an issue arising from the so-called 'diamond problem' where bird is derived from birdinterface and animal, and both birdinterface and animal are derived from the same class animalinterface. In this case bird contains 2 sets of data members inherited from class animalinterface.
See https://en.wikipedia.org/wiki/Virtual_inheritance for more info.

The solution is to make the inherited base class virtual. Note that laserlight's solution doesn't have this issue as bird is derived from animal and flyerinterface and animal is derived from eaterinterface.