diamond problem CPP(most asked in interview)

💎 Diamond Problem in C++ Explained

🔍 The Basic Scenario

• a. Suppose P is the base class.
• b. Class Q and R inherit from class P.
• c. Class S inherits from both Q and R.

Now, if P has a member (like a function), and S tries to access it, ambiguity arises: should it use the version from Q or from R?

⚠️ Problem Code (Ambiguous Inheritance)

#include <iostream>
using namespace std;

class A {
public:
    void show() { cout << "A::show" << endl; }
};

class B : public A { };
class C : public A { };

class D : public B, public C { };

int main() {
    D obj;
    obj.show(); // ❌ Error: request is ambiguous
}
      

✅ How We Solve It

C++ solves the diamond problem using virtual inheritance, which ensures only one shared copy of the base class.

✅ Solved Version Using Virtual Inheritance

#include <iostream>
using namespace std;

class A {
public:
    void show() { cout << "A::show" << endl; }
};

class B : virtual public A { };
class C : virtual public A { };

class D : public B, public C { };

int main() {
    D obj;
    obj.show(); // ✅ No ambiguity
}