OBJECT-ORIENTED PROGRAMMING CONCEPTS-CLASSES IVmercimek/courses/courses_Fall_2017/kom3191/files... · A Deeper Look at Classes 8 Objects as members of Classes Default Member-wise

OBJECT-ORIENTED PROGRAMMING

CONCEPTS-CLASSES IV

KOM3191 Object-Oriented Programming

1 KOM3191 Object Oriented Programming | Dr Muharrem Mercimek

Objects as members of Classes

KOM3191 Object Oriented Programming | Dr Muharrem Mercimek 2

Date.h



Date.cpp



Date.cpp



Employee.h



Employee.cpp

• Class Date does not provide a constructor

that receives a parameter of type Date.

• The compiler provides each class with a

default copy constructor. Each data

member is copied. birthDate=dateOfBirth;

hireDate=dateOfHire;

• If birthDate and hireDate are not const

parameters,

• then default memberwise assignment can

be used.

• Again no definition of such a constructor by

the user



Employee.cpp

A Deeper Look at

Classes

8


Default Member-wise Assignment

• Many classes must provide their own assignment operator

• To intelligently assign one object to another

• More about assignment of objects to each other when we get to Operator Overloading

• The '=' operator can be overloaded, just like any other

Copy Constructor • A constructor that copies another object of the same type

• Compiler provides a default copy constructor

• Copies each member of the original object into the corresponding member of the new object

• i.e., member-wise assignment

• Enables pass-by-value for objects • Used to copy original object’s values into new object to be passed to a function or

returned from a function

• Many classes must provide an explicit Copy Constructor

• To intelligently copy one object to another

KOM3191 Object Oriented Programming | Dr Muharrem Mercimek





test_Employee.cpp

11

friend Function of a Class

Ordinary Member Functions:

1. Function can access the private members of the class

2. Function is in the scope of the class

3. Function must be invoked on a specific object of the class – e.g.,

ptr -> func()

obj.func()


12

friend Function of a Class

• Defined outside that class’s scope.

• Not a member function of that class.

• Has right to access non-public and public members of that class.

• Often appropriate when a member function cannot be used for certain operations.

• Can enhance performance.


13

friend Functions and friend Classes

• To declare a function as a friend of a class:–

• Provide the function prototype in the class definition preceded by keyword friend

• To declare a class as a friend of another class:

• Place a declaration of the form

• friend class ClassTwo; in the definition of class ClassOne

• All member functions of class ClassTwo are friends of class ClassOne

• Friendship is granted, not taken.

• For class B to be a friend of class A, class A must explicitly declare that class B is its friend.

• Friendship relation is neither symmetric nor transitive

• If class A is a friend of class B, and class B is a friend of class C, cannot infer that

• class B is a friend of class A,

• class C is a friend of class B,

• class A is a friend of class C.


friend Functions and friend Classes


friend function declaration (can

appear anywhere in the class)

friend function can modify

Count’s private data

Calling a friend function; note that

we pass the Count object to the

function

15

this Pointer

• Member functions know which object’s data members to manipulate

• Every object has access to its own address through a pointer called this (a C++

keyword)

• An object’s this pointer is not part of the object itself

• The this pointer is passed (by the compiler) as an implicit argument to each of the

object’s non-static member functions

• Objects may use the this pointer implicitly or explicitly.

• this is used implicitly when accessing members directly.

• It is used explicitly when using keyword this.

• Type of the this pointer depends on

• type of the object, and

• whether member function is declared const.


16

this Pointer

Implicitly using the this pointer to access member x

Explicitly using the this pointer to access member x

Using the dereferenced this pointer and the dot operator


17

Cascaded member-function calls

• Multiple functions are invoked in the same statement.

• Enabled by member functions returning the dereferenced this pointer.

Time t;

t.setHour(15).setMinute( 30 ).setSecond( 22 );

Time& Time::setHour(int hr)

{

hour=hr;

return *this;

}


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OBJECT-ORIENTED PROGRAMMING CONCEPTS-CLASSES IVmercimek/courses/courses_Fall_2017/kom3191/files... · A Deeper Look at Classes 8 Objects as members of Classes Default Member-wise