CODEWITHSUNDEEP
c++solid-principles
ART
ART

Reputation: 1569

Interface segregation example C++

I was looking at oodesign website for interface segregation example

I understood the example and wrote below code in C++,

#include <iostream>

using namespace std;

class IWorkable {
public: 
    virtual void work() = 0;
};

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

// interface segregation principle - good example
class IWorker : public IFeedable, public IWorkable {
};

class Worker : public IWorkable, public IFeedable
{
public:
    void work() {
        cout << "working" <<endl;
    }

    void eat() {
        cout << "eating in launch break" <<endl;
    }
};

class SuperWorker : public IWorkable, public IFeedable{
public:
    void work() {
        cout << "working much more" << endl;
    }
    void eat() {
        cout << "eating in launch break" <<endl;
    }
};

class Robot :public IWorkable{
public:
    void work() {
        cout << "Robot working" <<endl;
    }
};

class Manager {
    IWorkable *worker;

public :
    void setWorker(IWorkable *w) {
        worker = w;
    }

    void manage() {
        worker->work();
    }
};

int main()
{
    IWorkable * w1 = new Worker();
    IWorkable * sw1 = new SuperWorker();
    IWorker *w2;
    Manager m1;
    m1.setWorker(w1);
    m1.manage();

    //When worker wants he can eat
    w2 = dynamic_cast<IWorker*>(w1);
    w2->eat();

    return 0;
}

When I run above code I get segmentation fault at w2->eat();

My guess is code is casting only pointer of IWorkable to IWorker which won't work because IWorkable doesn't have eat method.

If so what would be the solution in this case ? Any suggestion/pointer would help.

Note: I am trying it in C++98 however I am open to learn new way in C++11/14/17.

Upvotes: 1

Views: 1402

Answers (2)

Stephen Newell
Stephen Newell

Reputation: 7828

Your dynamic_cast is returning NULL since Worker doesn't inherit IWorker. By using the inheritance I assume you were going for, this works correctly.

class Worker : public IWorker { /* your same implmenetations */ };

Upvotes: 2

Paul Belanger
Paul Belanger

Reputation: 2434

You are accessing the pointer w2 without assigning it. Since a pointer value defaults to an undefined value, there is no guarantee that it points to a valid object. See: https://en.wikipedia.org/wiki/Dangling_pointer#Cause_of_wild_pointers

Upvotes: 1

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