solve diamond problem in c

What Is the Diamond Problem in C++? How to Spot It and How to Fix It

The Diamond Problem can arise in C++ when you use multiple inheritance. Here's what it is, how to spot it, and how to fix it.

Multiple inheritance in C++ is powerful, but a tricky tool, that often leads to problems if not used carefully—problems like the Diamond Problem.

In this article, we will discuss the Diamond Problem, how it arises from multiple inheritance, and what you can do to resolve the issue.

Multiple Inheritance in C++

Multiple Inheritance is a feature of Object-Oriented Programming (OOP) where a subclass can inherit from more than one superclass. In other words, a child class can have more than one parent.

The figure below shows a pictorial representation of multiple inheritances.

In the above diagram, class C has class A and class B as its parents.

If we consider a real-life scenario, a child inherits from its father and mother. So a Child can be represented as a derived class with “Father” and “Mother” as its parents. Similarly, we can have many such real-life examples of multiple inheritance.

In multiple inheritance, the constructors of an inherited class are executed in the order that they are inherited. On the other hand, destructors are executed in the reverse order of their inheritance.

Now let’s illustrate the multiple inheritance and verify the order of construction and destruction of objects.

Code Illustration of Multiple Inheritance

For the multiple inheritance illustration, we have exactly programmed the above representation in C++. The code for the program is given below.

The output we obtain from the above program is as follows:

Now if we check the output, we see that the constructors are called in order B, A, and C while the destructors are in the reverse order. Now that we know the basics of multiple inheritance, we move on to discuss the Diamond Problem.

The Diamond Problem, Explained

The Diamond Problem occurs when a child class inherits from two parent classes who both share a common grandparent class. This is illustrated in the diagram below:

Here, we have a class Child inheriting from classes Father and Mother . These two classes, in turn, inherit the class Person because both Father and Mother are Person.

As shown in the figure, class Child inherits the traits of class Person twice—once from Father and again from Mother. This gives rise to ambiguity since the compiler fails to understand which way to go.

This scenario gives rise to a diamond-shaped inheritance graph and is famously called “The Diamond Problem.”

Code Illustration of the Diamond Problem

Below we have represented the above example of diamond-shaped inheritance programmatically. The code is given below:

Following is the output of this program:

Now you can see the ambiguity here. The Person class constructor is called twice: once when the Father class object is created and next when the Mother class object is created. The properties of the Person class are inherited twice, giving rise to ambiguity.

Since the Person class constructor is called twice, the destructor will also be called twice when the Child class object is destructed.

Now if you have understood the problem correctly, let’s discuss the solution to the Diamond Problem.

How to Fix the Diamond Problem in C++

The solution to the diamond problem is to use the virtual keyword. We make the two parent classes (who inherit from the same grandparent class) into virtual classes in order to avoid two copies of the grandparent class in the child class.

Let’s change the above illustration and check the output:

Code Illustration to Fix the Diamond Problem

Here we have used the virtual keyword when classes Father and Mother inherit the Person class. This is usually called “virtual inheritance," which guarantees that only a single instance of the inherited class (in this case, the Person class) is passed on.

In other words, the Child class will have a single instance of the Person class, shared by both the Father and Mother classes. By having a single instance of the Person class, the ambiguity is resolved.

The output of the above code is given below:

Here you can see that the class Person constructor is called only once.

One thing to note about virtual inheritance is that even if the parameterized constructor of the Person class is explicitly called by Father and Mother class constructors through initialization lists, only the base constructor of the Person class will be called .

This is because there's only a single instance of a virtual base class that's shared by multiple classes that inherit from it.

To prevent the base constructor from running multiple times, the constructor for a virtual base class is not called by the class inheriting from it. Instead, the constructor is called by the constructor of the concrete class.

In the example above, the class Child directly calls the base constructor for the class Person.

Related: A Beginner's Guide to the Standard Template Library in C++

What if you need to execute the parameterized constructor of the base class? You can do so by explicitly calling it in the Child class rather than the Father or Mother classes.

The Diamond Problem in C++, Solved

The Diamond Problem is an ambiguity that arises in multiple inheritance when two parent classes inherit from the same grandparent class, and both parent classes are inherited by a single child class. Without using virtual inheritance, the child class would inherit the properties of the grandparent class twice, leading to ambiguity.

This can crop up frequently in real-world code, so it's important to address that ambiguity whenever it's spotted.

The Diamond Problem is fixed using virtual inheritance, in which the virtual keyword is used when parent classes inherit from a shared grandparent class. By doing so, only one copy of the grandparent class is made, and the object construction of the grandparent class is done by the child class.

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Diamond Problem in C++

The Diamond Inheritance Problem in C++ is something that can occur when performing multiple inheritance between Classes . Multiple Inheritance is the concept of inheriting multiple classes at once, instead of just one. If done incorrectly, it can result in the Diamond Problem.

What is the Diamond Inheritance Problem in C++?

The following image illustrates the situation under which the Diamond problem occurs.

The Class A, is inherited by both Class B and C. Then Class D performs multiple inheritance by inheriting both B and C. Now why does this cause a problem?

Well, let’s take a look at another diagram, that represents what actually ends up happening.

You may, or may not know, that when inheritance occurs between a parent and child class, an object of the parent is created and stored alongside the child object. That is how the functions and variables of the parent can be accessed.

Now if we apply this analogy to the above diagram, you will realize that the Object D, will end up having 4 more objects with it. Now the number of objects isn’t the problem, rather the problem is that we have two objects of Class A alongside Object D. This is a problem, because instead of one object, we have two objects of Class A. Other than performance reasons, what effect could this have? Let’s find out.

Problems caused by Diamond Inheritance

Let’s take a look at the actual code, and observe the problems being caused. As we mentioned earlier, due to Diamond Inheritance, the Object D will have two copies of Object A. Let’s run the below code to see proof of this fact.

As you can see, the Constructor for Class A was called twice, meaning two objects were created.

Digging Deeper in the Diamond Problem

Let’s take a look at a more detailed example, that shows a situation under which Diamond Inheritance can actually become a real problem, and throw an error.

Take a good look at this code. What we are doing here, is using the parameterized constructors to initialize the Objects for Class A. Class B and C are both passed two values, 5 and 8, which they both use to initialize to objects for Class A. One of the objects has the value 5, and one of them has the value 8.

The reason we did this, is so we can highlight the fact that there are two objects with two different values. Now the question is, when we try to use the getVar() function on object D, what happens? Normally, if there were just one object of Class A that was initialized to value “n”, the value “n” would be returned. But what happens in this case?

We can access each of the objects for Class A using the method above. Where we are performing the getVar() function on both the B and C Class object that are stored within Object D. As you can see, the value 5 and 8 are printed out.

But what happens when we use the getVar() function on D? Let’s find out.

See this error? It’s happening because it doesn’t know which object to use. It’s even showing in the error, that there are two objects which the getVar() function could be applied on.

How to solve the Diamond Problem in C++ using Virtual

The fix is very simple. All we need to do, is when inheriting when we make class B and class C inherit from Class A, we add the virtual keyword after the colon in the class name.

What this does, is shifts the responsibility of initializing Class A, to Class D. Previously Class B and C were responsible for initializing it, but since both were doing it, things became ambiguous. So if only Class D initializes Class A, there won’t be any problems as only one object is created.

Let’s modify our code now to include the Virtual keyword , and initialize Class A using Class D. (Although you can choose not to initialize it as well, and let the default constructor for Class A be used)

See our output now? There is no error, and only one object for Class A has been created. With this, our job is done and we can continue programming in peace.

This marks the end of the Diamond Problem in C++ Tutorial. Any suggestions or contributions for CodersLegacy are more than welcome. Questions regarding the tutorial content can be asked in the comments section below.

Multiple Inheritance in C++ and the Diamond Problem

by Onur Tuna

Unlike many other object-oriented programming languages, C++ allows multiple inheritance.

Multiple inheritance allows a child class to inherit from more than one parent class.

At the outset, it seems like a very useful feature. But a user needs to be mindful of a few gotchas while implementing this feature.

In the examples below, we will cover a few scenarios that one needs to be mindful about.

We’ll start with a simple example to explain this concept in C++.

The output of this code is as follows:

In the example above, we have a base class named as LivingThing . The Animal and Reptile classes inherit from it. Only the Animal class overrides the method breathe() . The Snake class inherits from the Animal and Reptile classes. It overrides their methods. In the example above, there is no problem. Our code works well.

Now, we’ll add a bit of complexity.

What if Reptile class overrides the breathe() method?

The Snake class would not know which breathe() method to call. This is the “Diamond Problem”.

Diamond Problem

Look at the code below. It is like the code in the example above, except that we have overridden the breathe() method in the Reptile class.

If you try compiling the program, it won’t. You’ll be staring at an error message like the one below.

The error is due to the “Diamond Problem” of multiple inheritance. The Snake class does not know which breathe() method to call.

In the first example, only the Animal class had overridden the breathe() method. The Reptile class had not. Hence, it wasn’t very difficult for the Snake class to figure out which breathe() method to call. And the Snake class ended up calling the breathe() method of the Animal class.

In the second example, the Snake class inherits two breathe() methods. The breathe() method of the Animal and Reptile class. Since we haven’t overridden the breathe() method in the Snake class, there is ambiguity.

C++ has many powerful features such as multiple inheritance. But, it is not necessary that we use all the features it provides.

I don’t prefer using multiple inheritance and use virtual inheritance instead.

Virtual inheritance solves the classic “Diamond Problem”. It ensures that the child class gets only a single instance of the common base class.

In other words, the Snake class will have only one instance of the LivingThing class. The Animal and Reptile classes share this instance.

This solves the compile time error we receive earlier. Classes derived from abstract classes must override the pure virtual functions defined in the base class.

I hope you enjoyed this overview of multiple inheritance and the “Diamond Problem”.

If this article was helpful, tweet it .

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Multiple Inheritance is a feature of C++ where a class can inherit from more than one classes. The constructors of inherited classes are called in the same order in which they are inherited. For example, in the following program, B’s constructor is called before A’s constructor.

A class can be derived from more than one base class.

(i) A CHILD class is derived from FATHER and MOTHER class (ii) A PETROL class is derived from LIQUID and FUEL class.

The destructors are called in reverse order of constructors.

In the above program, constructor of ‘Person’ is called two times. Destructor of ‘Person’ will also be called two times when object ‘ta1’ is destructed. So object ‘ta1’ has two copies of all members of ‘Person’, this causes ambiguities. The solution to this problem is ‘virtual’ keyword . We make the classes ‘Faculty’ and ‘Student’ as virtual base classes to avoid two copies of ‘Person’ in ‘TA’ class.

For example, consider the following program.

In the above program, constructor of ‘Person’ is called once. One important thing to note in the above output is, the default constructor of ‘Person’ is called . When we use ‘virtual’ keyword, the default constructor of grandparent class is called by default even if the parent classes explicitly call parameterized constructor.

How to call the parameterized constructor of the ‘Person’ class?

The constructor has to be called in ‘TA’ class.

For example, see the following program.

In general, it is not allowed to call the grandparent’s constructor directly, it has to be called through parent class. It is allowed only when ‘virtual’ keyword is used.

As an exercise, predict the output of following programs.

Question 1

Question 2

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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C++: Diamond Problem and Virtual Inheritance

Summary: In this tutorial, we will learn what the diamond problem is, when it happens and how we can solve it using virtual inheritance in C++.

What is the Diamond Problem?

When we inherit more than one base class in the same derived class and all these base classes also inherit another but same single class (super parent), multiple references of the super parent class become available to the derived class.

So, it becomes unclear to the derived class, which version of the super parent class it should refer to.

Consider the following program for instance:

There is no syntactical error in the above program but still, if we try to compile then it returns the following compilation error:

line 24|error: request for member ‘name’ is ambiguous

This is because two instances of class A’s name() method is available for class D, one through class B, and the other through class C.

In this case, the compiler gets confused and cannot decide which name() method it should refer to.

This ambiguity often occurs in the case of multiple inheritances and is popularly known as the diamond problem in C++.

To remove this ambiguity, we use virtual inheritance to inherit the super parent.

What is Virtual Inheritance?

Virtual inheritance in C++ is a type of inheritance that ensures that only one copy or instance of the base class’s members is inherited by the grandchild derived class.

It is implemented by prefixing the virtual keyword in the inheritance statement.

If we now apply virtual inheritance in our previous example, only one instance of class A would be inherited by class D (i.e. B::A and C::A will be treated as the same).

Now because there is only one reference of class A’s instance is available to the child classes, we get the proper diamond-shaped inheritance.

Also, If we need to override any of the super parent class’s method (class A) in the child classes, we should override it till the very derived class, like the following. Otherwise, the compiler will throw no unique overrider error .

In this tutorial, we understood the concept of virtual inheritance and were able to solve the diamond problem using the same in C++.

Multiple Inheritance in C++

The capability of a class to derive properties and characteristics from another class is called Inheritance. This allows us to reuse and modify the attributes of the parent class using the object of the derived class.

The class whose member functions and data members are inherited is called the base class or parent class, and the class that inherits those members is called the derived class.

Introduction to Multiple Inheritance

Multiple Inheritance is the concept of inheritance in C++ by which we can inherit data members and member functions from multiple(more than one) base/parent class(es) so that the derived class can have properties from more than one parent class.

In the image above, the derived class inherits data members and member functions from two different parent classes named Base Class 1 and Base Class 2 .

SHOWING AN EXAMPLE ANALOGY OF FLYING CAR AS MULTIPLE INHERITANCE

Diagram of Multiple Inheritance in C++

Syntax of Multiple Inheritance in C++

Here, there are two base classes: BaseClass1 and BaseClass2 . The DerivedClass inherits properties from both the base classes.

While we write the syntax for the multiple inheritance, we should first specify the derived class name and then the access specifier (public, private, or protected), and after that, the name of base classes.

We should also keep in mind the order of the base classes given while writing the multiple inheritance because the base class's constructor, which is written first, is called first.

As the order while writing the multiple inheritance was BaseClass2 and then BaseClass1 , the constructor will be called in that order only.

Now, changing the order.

Ambiguity Problem in Multiple Inheritance

In multiple inheritance, we derive a single class from two or more base or parent classes.

So, it can be possible that both the parent classes have the same-named member functions. While calling via the object of the derived class(if the object of the derived class invokes one of the same-named member functions of the base class), it shows ambiguity.

The online C++ compiler gets confused in selecting the member function of a class for the execution of a program and gives a compilation error.

Program to demonstrate the Ambiguity Problem in Multiple Inheritance in C++

Ambiguity Resolution in Multiple Inheritance

This problem can be solved using the scope resolution (::) operator. Using the scope resolution operator, we can specify the base class from which the function is called. We need to use the scope resolution (::) operator in the main() body of the code after we declare the object and while calling the member function by the object.

Ambiguity Resolved Code

How does multiple inheritance differ from multilevel inheritance.

DIAGRAM OF BOTH MULTIPLE AND MULTILEVEL INHERITANCE

Syntax of Multiple Inheritance:

The Diamond Problem

A diamond pattern is created when the child class inherits from the two base/parent class, and these parent classes have inherited from one common grandparent class(superclass).

Here, you can see that the superclass is called two times because of the diamond problem.

Solution of the Diamond Problem: The solution is to use the keyword virtual on the two parent classes, ClassA and ClassB . Two-parent classes with a common base class will now inherit the base class virtually and avoid the occurrence of copies of the base class in the child class ( ClassC here). This is called virtual inheritance. The virtual inheritance limits the passing of more than a single instance from the base class to the child class.

Fixed Code for the Diamond Problem

Output The result shows that ambiguity is removed using the virtual keyword:

Here in the output, we can see that the superclass's members are only inherited and have not formed copies.

TWO DIAGRAMS SHOWING HOW VIRTUAL INHERITANCE HELPS

How to Call the Parameterized Constructor of the Base Class?

To call the parameterized constructor of the base class, we need to explicitly specify the base class’s parameterized constructor in the derived class when the derived class’s parameterized constructor is called.

The parameterized constructor of the base/parent class should only be called in the parameterized constructor of the subclass. It cannot be called in the default constructor of the subclass.

Code Syntax:

Visibility Modes in Multiple Inheritance in C++

The visibility mode specifies the control/ accessibility over the inherited members of the base class within the derived classes. In C++, there are three visibility modes- public , protected , and private . The default visibility mode is private.

Private Visibility Mode: In Inheritance with private visibility mode, the public members(data members and member functions) and protected members of the parent/base classes become ‘private members' in the derived class.

Protected Visibility Mode: In inheritance with protected visibility mode, the public members(data members and member functions) and the protected members of the base/parent class become protected members of the derived class. As the private members are not inherited, they are not accessible directly by the object of the derived class. The difference between the private and the protected visibility mode is-

Public Visibility Mode: In inheritance with public visibility mode, the public members(data members and member functions) of the base class(es) are inherited as the public members in the derived class, and the protected members(data members and member functions) of the base class are inherited as protected members in the derived class.

Advantages of Multiple Inheritance in C++

Multiple Inheritance is the inheritance process where a class can be derived from more than one parent class. The advantage of multiple inheritances is that they allow derived classes to inherit more properties and characteristics since they have multiple base/parent classes.

Example of Multiple Inheritance in C++

In the example of Multiple Inheritance, we will calculate the average of the two subjects.

The two subjects will have two different classes, and then we will make one class of Result which will be the derived class from the above two classes through multiple inheritance.

Now, we can access the member functions and data members directly when we inherit in public mode. We will use the data of both the parent classes, and then we will calculate the average marks.

The capability of a class to derive properties and characteristics from another class is called Inheritance.
Base Class - A class whose members are inherited.
Derived Class - A class that inherits the base class members.
In Multiple Inheritance in C++, we can inherit data members and member functions from multiple(more than one) base/parent class(es).
When the base classes have the same-named member functions and when we call them via derived class object. It shows ambiguity.
To solve the ambiguity problem, we should use the scope resolution operator (::) .
A diamond pattern is created when the child class inherits values and functions from the two base/parent classes, and these parent classes have inherited their values from one common grandparent class(superclass), which leads to duplication of functions.
To solve the diamond problem, we should use the virtual keyword, which restricts the duplicate inheritance of the same function.
There are three visibility modes in C++ for inheritance - public , protected , and private . The default visibility mode is private.
Polymorphism in C++ .

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How to calculate hp in dnd 5e

How to calculate hp 5e, how to calculate hp, how to calculate how tall i will be, how to calculate how pregnant you are, how to calculate how much you need to retire, how to calculate how much you make an hour, how to calculate how much you make a year, how to calculate how much you make a month, how to calculate how much water to drink, what is the diamond problem in c++ how to spot it and how to fix it.

C++ is a popular programming language used for a variety of applications. However, like any programming language, it has its quirks and challenges. One such challenge is known as the diamond problem, which occurs when multiple inheritance is used in a class hierarchy. This article will explore what the diamond problem is, how to spot it, and how to fix it.

What Is the Diamond Problem?

The diamond problem occurs in C++ when two classes inherit from a common base class, and a third class inherits from both of these classes. The resulting class hierarchy resembles a diamond shape, with the common base class at the top of the diamond and the two derived classes at the bottom corners. This makes it difficult for the third class, which inherits from both derived classes, to know which version of the inherited method to use. This can result in conflicts and ambiguity in the program.

How to Spot the Diamond Problem

To spot the diamond problem, look for a class hierarchy that resembles a diamond shape, as described above. If there are multiple derived classes that inherit from a common base class and a third class that inherits from both of these derived classes, the diamond problem is likely to occur.

Additionally, if there are conflicting methods or variables in the derived classes, this can also indicate the diamond problem. The third class that inherits from both derived classes may not know which version of the method to use, leading to conflicts and ambiguity in the program.

How to Fix the Diamond Problem

There are several ways to fix the diamond problem in C++. One solution is to use virtual inheritance, which ensures that only one instance of the base class is created in the derived class hierarchy. This eliminates the ambiguity and conflicts that arise in the diamond problem.

Virtual inheritance is implemented by using the keyword “virtual” when inheriting from the common base class. This tells the compiler to create a single instance of the base class in the derived class hierarchy. The syntax for virtual inheritance looks like this:

class Base {

class Derived1 : virtual public Base {

class Derived2 : virtual public Base {

class Third : public Derived1, public Derived2 {

In this example, both Derived1 and Derived2 inherit virtually from the Base class, and the Third class inherits from both Derived1 and Derived2.

Another solution is to use composition instead of inheritance. This involves creating an object of the base class inside the derived class, rather than inheriting from it. This reduces the complexity of the class hierarchy and eliminates the diamond problem.

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How to solve the Diamond Problem without using virtual function [closed]

i have this code as an example and we were given an openbook task to search for an answer on how to solve this code without using virtual keyword. i tired searching on google and tried myself but couldnt do it. so can anyone help?

diamond-problem

1 Assuming the dozen compile-time errors in this code will take care of themselves? – WhozCraig Apr 12, 2022 at 5:10
A book will not be enough... he also needs a compiler. As we see the code, it was never tried to compile it. – Klaus Apr 12, 2022 at 6:15
Solve what exactly? What is the problem? – n. m. could be an AI Apr 12, 2022 at 6:16

Browse other questions tagged c++ diamond-problem or ask your own question .

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how can we solve diamond problem in c

What is the diamond problem in c++ how to spot it and how to fix it.

The Diamond Problem can arise in C++ when you use multiple inheritance. Here's what it is, how to spot it, and how to fix it.

Multiple inheritance in C++ is powerful, but a tricky tool, that often leads to problems if not used carefully—problems like the Diamond Problem.

In this article, we will discuss the Diamond Problem, how it arises from multiple inheritance, and what you can do to resolve the issue.

Multiple Inheritance in C++

Multiple Inheritance is a feature of Object-Oriented Programming (OOP) where a subclass can inherit from more than one superclass. In other words, a child class can have more than one parent.

The figure below shows a pictorial representation of multiple inheritances.

In the above diagram, class C has class A and class B as its parents.

Now let’s illustrate the multiple inheritance and verify the order of construction and destruction of objects.

Code Illustration of Multiple Inheritance

For the multiple inheritance illustration, we have exactly programmed the above representation in C++. The code for the program is given below.

The output we obtain from the above program is as follows:

The Diamond Problem, Explained

The Diamond Problem occurs when a child class inherits from two parent classes who both share a common grandparent class. This is illustrated in the diagram below:

Here, we have a class Child inheriting from classes Father and Mother . These two classes, in turn, inherit the class Person because both Father and Mother are Person.

This scenario gives rise to a diamond-shaped inheritance graph and is famously called “The Diamond Problem.”

Code Illustration of the Diamond Problem

Below we have represented the above example of diamond-shaped inheritance programmatically. The code is given below:

Following is the output of this program:

Since the Person class constructor is called twice, the destructor will also be called twice when the Child class object is destructed.

Now if you have understood the problem correctly, let’s discuss the solution to the Diamond Problem.

How to Fix the Diamond Problem in C++

Let’s change the above illustration and check the output:

Code Illustration to Fix the Diamond Problem

The output of the above code is given below:

Here you can see that the class Person constructor is called only once.

This is because there's only a single instance of a virtual base class that's shared by multiple classes that inherit from it.

In the example above, the class Child directly calls the base constructor for the class Person.

Related: A Beginner's Guide to the Standard Template Library in C++

What if you need to execute the parameterized constructor of the base class? You can do so by explicitly calling it in the Child class rather than the Father or Mother classes.

The Diamond Problem in C++, Solved

This can crop up frequently in real-world code, so it's important to address that ambiguity whenever it's spotted.

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Diamond Problem in Inheritance

Diamond problem occurs when we use multiple inheritance in programming languages like C++ or Java.

Let’s understand this with one example.

Suppose there are four classes A, B, C and D. Class B and C inherit class A. Now class B and C contains one copy of all the functions and data members of class A.

Class D is derived from Class B and C. Now class D contains two copies of all the functions and data members of class A. One copy comes from class B and another copy comes from class C.

Let’s say class A have a function with name display(). So class D have two display() functions as I have explained above. If we call display() function using class D object then ambiguity occurs because compiler gets confused that whether it should call display() that came from class B or from class C. If you will compile above program then it will show error.

This kind of problem is called diamond problem as a diamond structure is formed (see the image).

How to Remove Diamond Problem in C++?

We can remove diamond problem by using virtual keyword. It can be done in following way.

You can see we have marked class B and C as virtual. Now compiler takes care that only one copy of data members and functions of class A comes to class D.

How to Remove Diamond Problem in Java?

To remove this problem java does not support multiple inheritance . Although we can achieve multiple inheritance using interfaces.

Comment below if you found anything missing or incorrect in above diamond problem tutorial.

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Introduction to object oriented programming concepts in java, classes and objects in java, this keyword in java, polymorphism in java, 1 thought on “diamond problem in inheritance”.

In the above mentioned code, after virtually inheriting class A to both the classes B and C, it still doesn’t solves the problem.

Referring to your above code, if I call – int main() { D d1; d1.display(); /* It will still give compiler error, since display is overridden in both the classes B and C and it will still have 2 copies in class D (one from B and one from C) so here there will be ambiguity between class B::display() and C::display()*/ }

Please check and update accordingly, it seems quite misleading.

Thanks Amit

Diamond Problem in C++

What is the Diamond Inheritance Problem in C++?

The following image illustrates the situation under which the Diamond problem occurs.

The Class A, is inherited by both Class B and C. Then Class D performs multiple inheritance by inheriting both B and C. Now why does this cause a problem?

Well, let’s take a look at another diagram, that represents what actually ends up happening.

Problems caused by Diamond Inheritance

As you can see, the Constructor for Class A was called twice, meaning two objects were created.

Digging Deeper in the Diamond Problem

Let’s take a look at a more detailed example, that shows a situation under which Diamond Inheritance can actually become a real problem, and throw an error.

But what happens when we use the getVar() function on D? Let’s find out.

See this error? It’s happening because it doesn’t know which object to use. It’s even showing in the error, that there are two objects which the getVar() function could be applied on.

How to solve the Diamond Problem in C++ using Virtual

The fix is very simple. All we need to do, is when inheriting when we make class B and class C inherit from Class A, we add the virtual keyword after the colon in the class name.

See our output now? There is no error, and only one object for Class A has been created. With this, our job is done and we can continue programming in peace.