2.3. Member Access Specifiers

2.3. Member Access Specifiers
	Chapter 2. Top of the `class`

[ fromfile: classes.xml id: memberaccess ]

Client code is code that is outside the scope of the class, but which uses objects or members of that class.
client code #includes the header file that contains the class definition.
In Example 2.5, you can see that fraction.h contains class definition code of Fraction, and is itself a client of QString.

Example 2.5. src/classes/fraction/fraction.h

#ifndef _FRACTION_H_ 
#define _FRACTION_H_  

#include <QString>


class Fraction {
public:
    void set(int numerator, int denominator);
    double toDouble() const;
    QString toString() const;
private:
    int m_Numerator;
    int m_Denominator;
};

#endif

The access specifiers, public, protected, and private, are used in a class definition to specify where in a program the affected members can be accessed.
The following list provides an informal first approximation of the definitions of these three terms.
Refinements are contained in footnotes.
- A public member can be accessed (using an object of the class)^[13] anywhere in a program that #includes the class definition file.
- A protected member can be accessed inside the definition of a member function of its own class, or a member function of a derived class.^[14]
- A private member is only accessible by member functions of its own class.^[15]
Class members are private by default.

Example 2.6. src/classes/fraction/fraction-client.cpp

#include <QTextStream>
#include "fraction.h"

int main() {
    const int DASHES = 30;
    QTextStream cout(stdout);
    
    {                                   
        int i;
        for (i = 0; i < DASHES; ++i)
            cout << "=";
        cout << endl;
    }   

    cout << "i = " << i << endl;        
    Fraction f1, f2;
    f1.set(3, 4);
    f2.set(11,12);                      
    f2.m_Numerator = 12;                
    cout << "The first fraction is: " << f1.toString() << endl;
    cout << "\nThe second fraction, expressed as a double is: "
         << f2.toDouble() << endl;
    return 0;
}

	Nested scope, inner block.
	Error: i no longer exists, so it is not visible in this scope.
	Set through a member function.
	Error, m_Numerator is visible but not accessible.

^[13]public static members can be accessed without an object. We discuss this in Section 2.9.

^[14]Chapter 6 discuss derived classes.

^[15]Private members are also accessible by friends of the class, which we discuss in Section 2.6.


2.2. Class Definitions		2.4. Encapsulation