Curriculum

Learn C++ Programming

Exploring the Classes and Objects in C++ - Part 1

0/8

Functions in C++

0/11

Working with Constructor and Destructor in C++

0/7

Chapter 1: Inroduction to C++

0/6

Exploring the Classes and Objects in C++ - Part 2

0/10

Chapter 2: Fundamentals of C++

0/4

Chapter 3: Working with Arrays in C++

0/2

Understanding Pointers in C++

0/2

Working with Strings in C++

0/8

Friend Functions and Classes in C++

0/8

Operator Overloading in C++

0/6

Working with Inheritance in C++: Part 1

0/7

Working with Inheritance in C++: Part 2

0/5

Working with Pointers and Polymorphism in C++

0/7

Exception Handling in C++

0/7

Templates in C++

0/5

Standard Template Library(STL) in C++

0/4

Working with I/O Stream and Files in C++

0/2

Text lesson

Granting Access

[post-views]

In this lesson, you will learn,

Granting Access to Private Data
Example

Granting Access to Private Data

You know, when a base class is inherited as private, all public and protected members of that class become private members of the derived class.

For example, in some circumstances, you might want to grant certain public members of the base class public status in the derived class even though the base class is inherited as private mode.

You can restore an inherited member’s access specification by employing an access declaration within the derived class.

An access declaration takes this general form:

base-class::member;

Notice that no type declaration is required (or, indeed, allowed) in an access declaration.

Example

class Base {
public:
    int j; // public in base
};

// Inherit base as private.
class Derived: private Base {
public:
    // here is access declaration
    Base::j; // make j public again
};

Example: Access Declaration

//GrantingAccessEx2.cpp
#include <iostream>
using namespace std;

class base {
    int i; // private to base
public:
    int j, k;
    void seti(int x) { i = x; }
    int geti() { return i; }
};

// Inherit base as private.
class derived: private base {
public:
    /* The next three statements override
    base's inheritance as private and restore j,
    seti(), and geti() to public access. */
    
    base::j; // make j public again - but not k
    base::seti; // make seti() public
    base::geti; // make geti() public
    
    // base::i; // illegal, you cannot elevate access
    int a; // public
};
int main()
{
    derived ob;
    //ob.i = 10; // illegal because i is private in derived
    ob.j = 20; // legal because j is made public in derived
    
    //ob.k = 30; // illegal because k is private in derived
    ob.a = 40; // legal because a is public in derived
    
    ob.seti(10);
    cout << ob.geti() << " " << ob.j << " " << ob.a;
    return 0;
}

Output

using-declarations; suggestion: add the 'using' keyword [-Wdeprecated]
     base::seti; // make seti() public
     ^~~~
GrantingAccessEx2.cpp:22:5: warning: access declarations are deprecated in favour of 
using-declarations; suggestion: add the 'using' keyword [-Wdeprecated]
     base::geti; // make geti() public
     ^~~~
10 20 40

Access declarations are currently supported by Standard C++, but they are deprecated.

End of the lesson….enjoy learning

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