In c plus plus what is the purpose of the keyword public and private in the definition of a class?

Answer 1

Public members/functions can be accessed from outside the class, private members/functions can only be accessed from functions of that class.

Ex.

class sampleClass{

private int value;

public void setValue(int a){value = a;} /* legal, value can be accessed since this is a method within the same class */

public int getValue(){return value;}

};

int main()

{

sampleClass sc; // class is instantiated

sc.setValue(5); // legal, setValue() is public

sc.value = 7; // ERROR, value is private, will not compile

printf("%d\n", sc.getValue()); // Will print 5

return 0;

}

Answer 2

The public, protected and private keywords define the accessibility of your class interface. Private members are fully accessible to the class and to friends of the class. An instance of a class is automatically granted friend access to all other instances of the same class. Protected members are similar to private members but are also accessible to derived classes. Public members are fully-accessible.

Derived classes can also modify access to their inherited class members. Public inheritance does not alter the base class interface. Protected inheritance alters the public members so they are protected in the derived class. Private inheritance alters all public and protected members so they are all private in the derived class. Access to individual public and protected members can also be altered on a member-by-member basis allowing finer control over the inherited interface, however private members remain private to the base class as they are never inherited.