What does the following program do? Explain why. [***This is the NEW question) #include class A { public: void f() { std::cout << "A"; } } ; class B : public A { public: void f() { std::cout << "B"; } } ; void g(A &a) { a.f(); }| int main(O { B b; g (b) ; }

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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### Program Explanation

The provided C++ program demonstrates the concept of inheritance and function overriding in an object-oriented paradigm. Here's a detailed explanation:

#### Code:
```cpp
#include <iostream>

class A {
public:
    void f() { std::cout << "A"; }
};

class B : public A {
public:
    void f() { std::cout << "B"; }
};

void g(A &a) { a.f(); }

int main() {
    B b;
    g(b);
}
```

#### Explanation:
- **Class A and B:** 
  - `class A` has a public member function `f()` which prints `"A"`.
  - `class B` inherits from `class A` and overrides the function `f()` to print `"B"`.

- **Function `g(A &a):`**
  - It takes a reference to an object of type `A` and calls its `f()` method.

- **`main()` function:**
  - An object `b` of type `B` is created.
  - The function `g()` is then called with `b` as an argument.

#### Polymorphic Behavior:
- Even though `g()` takes a reference to `A`, the function `f()` of class `A` is called. This is due to the fact that `f()` is not declared as virtual in `A`, so the function call is resolved at compile time and not run time, this leads to the invocation of `A::f()` rather than `B::f()`.

#### Output:
- The output of the program will be `A`.

#### Conclusion:
- This program illustrates the importance of declaring methods as `virtual` to achieve polymorphism in C++. Without the `virtual` keyword, the base class function is called instead of the derived class version when using base pointers or references, due to static binding. 

For educational purposes, it would be beneficial to modify the program to demonstrate dynamic polymorphism, by declaring `f()` in class `A` as virtual.
Transcribed Image Text:### Program Explanation The provided C++ program demonstrates the concept of inheritance and function overriding in an object-oriented paradigm. Here's a detailed explanation: #### Code: ```cpp #include <iostream> class A { public: void f() { std::cout << "A"; } }; class B : public A { public: void f() { std::cout << "B"; } }; void g(A &a) { a.f(); } int main() { B b; g(b); } ``` #### Explanation: - **Class A and B:** - `class A` has a public member function `f()` which prints `"A"`. - `class B` inherits from `class A` and overrides the function `f()` to print `"B"`. - **Function `g(A &a):`** - It takes a reference to an object of type `A` and calls its `f()` method. - **`main()` function:** - An object `b` of type `B` is created. - The function `g()` is then called with `b` as an argument. #### Polymorphic Behavior: - Even though `g()` takes a reference to `A`, the function `f()` of class `A` is called. This is due to the fact that `f()` is not declared as virtual in `A`, so the function call is resolved at compile time and not run time, this leads to the invocation of `A::f()` rather than `B::f()`. #### Output: - The output of the program will be `A`. #### Conclusion: - This program illustrates the importance of declaring methods as `virtual` to achieve polymorphism in C++. Without the `virtual` keyword, the base class function is called instead of the derived class version when using base pointers or references, due to static binding. For educational purposes, it would be beneficial to modify the program to demonstrate dynamic polymorphism, by declaring `f()` in class `A` as virtual.
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