c++ class multiple inheritance

You have learned from day-07 about c++ inheritance. A c++ class can not only inherit one class, but also inherit more than one class. If a c++ class is derived from at least two classes, that is multiple inheritance.

Multiple inheritance

Any one of C, D, E, F declarations are multiple inheritance, as any one of them is derived from at least two classes.

class A {};
class B {};
class C: public A, public B {};
class D: public A, protected B {};
class E: private A, private B {};
class F: public A, protected B, private C {};

Not multiple inheritance

There is no multiple inheritance here. Although A is inherited by many classes, it is still single inheritance.

class A {};
class B: public A {};
class C: protected A {};
class D: private A {};

Diamond Inheritance

If a class is derived from multiple classes which are derived from the same class, that is diamond inheritance.

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

B and C are derived from the same class A, D is derived from B and C, that's diamond inheritance.

Method overloading of inheritance

If method overloading (the same method name) happens on many classes of inheritance, the class_name::method_name can be used to distinguish them when that method is called.

For example:

namespace my_space::diamond
{

class A
{
public:
	void fz_k() const {}
	void fz_j() const {}
};

class B
{
public:
	void fz_k() const {}
};

class c_class: public A, public B
{
public:
	void eater() const
	{
		A::fz_k();	// A:: is used here to distinguish.
		B::fz_k();	// B:: is used here to distinguish.
		fz_j();	// A::fz_j() can be used here too, but only A has fz_j, so A:: can be omitted.
	}
};

}	// namespace my_space::diamond

int main()
{
	auto object = my_space::diamond::c_class{};
}

(You have learned method const, namespace from day-11)

c++ Diamond multiple inheritance example

#include <iostream>

namespace my_space::diamond
{

class base_class
{
public:
	void gy_p() const
	{
		std::cout << "base_class gy_p" << std::endl;
	}
};

class derived_1: public base_class
{
public:
	void gy_p() const
	{
		std::cout << "derived_1 gy_p" << std::endl;
	}
};

class derived_2: public base_class
{
public:
	void gy_p() const
	{
		std::cout << "derived_2 gy_p" << std::endl;
	}
	void gy_r() const
	{
		std::cout << "derived_2 gy_r" << std::endl;
	}
};

class diamond_class: public derived_1, public derived_2
{
public:
	void w_p() const
	{
		derived_1::gy_p();
		derived_2::gy_p();
		// base_class::gy_p();	// Ambiguous error here, this will be talked next

		derived_2::gy_r();
		gy_r();	// same, gy_r is only declared in derived_2
	}
};

}	// namespace my_space::diamond

int main()
{
	auto diamond = my_space::diamond::diamond_class{};
	diamond.w_p();
}

output:

derived_1 gy_p
derived_2 gy_p
derived_2 gy_r
derived_2 gy_r

Written on Oct 31, 2024

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