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C++ OOP
course content

Conteúdo do Curso

C++ OOP

C++ OOP

1. Fundamentals of OOP in C++
Introduction to Object-Oriented Programming in C++Why use Object-Oriented Programming?Class Creation SyntaxAttributes of the ClassMethods of the ClassStatic Members of The ClassThe This KeywordClasses and Objects Overview
2. Constructors and Destructors
What is a Constructor of the ClassConstructor and AttributesConstructor Initialization ListInitialization List PracticeConstructor DelegationConstructor Delegation PracticeWhat is a Destructor of the ClassCopy ConstructorsConstructors and Destructors Practice
3. Encapsulation Overview
Introduction to EncapsulationAccess Modifiers KeywordsAccess Modifiers PracticeAccessor and Mutator MethodsAccess and Mutator PracticeSegmentation and AggregationThe Friend Keyword
4. Inheritance Overview
Introduction to InheritanceAccess Modifiers in InheritanceMulptiple InheritanceConstructor and Destructor in InheritanceDiamond InheritanceThe Final Keyword
5. Polymorphism Overview
Introduction to PolymorphismVirtual and Override KeywordsPure Virtual MethodOperator OverloadingSummary and Overview

book
The Friend Keyword

The friend keyword stands as a unique construct, offering a departure from the standard encapsulation principles of object-oriented programming. It allows a function or another class to access private and protected members of a class.

cpp

main

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#include <iostream>

class Example {
private:
    const static int static_private_member = 0;
    friend void func(); // grants access to the private members to func()
};

void func()
{ 
    std::cout << Example::static_private_member << std::endl; 
}

int main() 
{
    func();
}

Using this approach breaks encapsulation because it lets outside entities access the class members. However, there might be situations where it's necessary to do so. For instance:

h

KeyManager

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class KeyManager {
public:
    KeyManager(const std::string& key) : encryptionKey(key) {}
private:
    std::string encryptionKey;
};

In this example, the encryptionKey is kept private, and there is no accessor method provided because we want to prevent external access to it from outside the class. But what if there is a necessity to use an external algorithm for encrypting and decrypting, this is where the friend keyword comes into play.

h

KeyManager

h

CryptographicAlgorithm

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#include "CryptographicAlgorithm.h"

class KeyManager {
public:
    KeyManager(const std::string& key) : encryptionKey(key) {}
private:
    std::string encryptionKey;
    // Allow CryptographicAlgorithm access to private members
    friend class CryptographicAlgorithm; 
};

The most common use-case for friend keyword arises when quick fixes are required, and you intend to refactor it later. It's preferable to design your class relationships without relying on it, although specific scenarios may still occur.

question mark

What is the friend keyword used for?

Select the correct answer

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Seção 3. Capítulo 7
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