Chapter 4 OOPS WITH C++ Sahaj Computer Solutions

Transcription

1 Chapter 4 OOPS WITH C++ Sahaj Computer Solutions 1

2 Session Objectives Classes and Objects Class Declaration Class Members Data Constructors Destructors Member Functions Class Member Visibility Private, Public,Protected The scope of the class object constructor OOPS WITH C++ Sahaj Computer Solutions 2

3 Session objectives Default Constructor Constructor with arguments Constructor with default arguments Dynamic constructor Copy Constructor Overloaded Constructor Objects as Function arguments Member functions defined outside the class. Objects as arguments OOPS WITH C++ Sahaj Computer Solutions 3

4 Session Objectives Returning objects from functions Class array as class member data Array of objects String as class member. OOPS WITH C++ Sahaj Computer Solutions 4

5 Accessing Class Members To access the members of the class we make use of the DOT(.) Operator. Syntax: Object-name.function-name(actual arguments) Example: x.getdata(100,75.5); OOPS WITH C++ Sahaj Computer Solutions 5

6 Defining Member Functions Member functions can be defined in two places. Outside the Class definition Inside the class definition Outside the Class Definition Member functions that are declared inside the class have to e defined separately outside the class. Their definition is much like normal functions. They should have a function header and a body. OOPS WITH C++ Sahaj Computer Solutions 6

7 Outside the Class Definition An important difference between a member function and a normal function is that a member function incorporates a membership identity label in the header. This label tells the compiler which class the function belongs to. The general form of a member-function definition is : return-type class-name:: function-name(argument declaration) { } Function-Body OOPS WITH C++ Sahaj Computer Solutions 7

8 Outside the Class Definition The membership label class-name:: tells the compiler that the function-name belongs to the class-name. That is the scope of the function is restricted to the class name specified in the header line. The symbol :: is called the scope resolution operator. Example: void sum::getdata(int a,int b) { sum=a+b; } OOPS WITH C++ Sahaj Computer Solutions 8

9 Defining Member Functions The member functions have some special characteristics that are often used in the program development: Several different classes can use the same function name. The membership label will resolve their scope. Member functions can access the private data of the class. A non-member function cannot do so. A member function can call another member function directly, without using the dot operator. OOPS WITH C++ Sahaj Computer Solutions 9

10 Inside the class definition Another method of declaring a member function is to replace the function definition by the actual definition. Example class sum{ int a,b; public: }; void getdata(int x,int y) { a=x; b=y } OOPS WITH C++ Sahaj Computer Solutions 10

11 Making Outside function Inline A member function outside the class definition can still be made inline by using the qualifier inline. Example: class item{ :::::::::::::::::: public: void getdata(int a,int b); }; inline void item::getdata(int a,int b) { :::::::::::::::::::::: } OOPS WITH C++ Sahaj Computer Solutions 11

12 Nesting Member Functions As discussed earlier a member function of a class can be called by an object of that class using the dot operator. However there is an exception to this. A member function can be called by using its name inside another member function of that same class. This is known as nesting of member functions Program:CH4PG7.cpp OOPS WITH C++ Sahaj Computer Solutions 12

13 Arrays within a class Arrays can be used as member variables in a class For example: class arraydemo{ inta[20]; public: void getval(){ for(int i=0;i<n;i++) cin>>a[i]; } }; Program: CH4PG8.cpp OOPS WITH C++ Sahaj Computer Solutions 13

14 Memory Allocation for Objects Class Member variable 1 Member variable 2 Member function1 Member function2 Member variable 1 Member variable 2 Member variable 1 Member variable 2 Member variable 1 Member variable 2 Object A Object B Object C OOPS WITH C++ Sahaj Computer Solutions 14

15 Static Data Members Whenever a object is created a new copy of data variables is created for that object. This means that each objects works on its own copy of data variables. C++ uses another type of variable declaration called as static. A data member of class can be qualified as static The static member variable has certain special characteristics. OOPS WITH C++ Sahaj Computer Solutions 15

16 Static Data Members These are: It is initialized to zero when the first object of its class is created. No other initialization is permitted. Only one copy of that member is created for the entire class and is shared by all the objects of that class, no matter how many objects are created. It is visible only within the class, but its lifetime is the entire program. OOPS WITH C++ Sahaj Computer Solutions 16

17 Static Data Members PROGRAM:CH4PG9.CPP int item :: count ; Note that the type and scope of each static member variable must be defined outside the class definition. This is necessary because the static data members are stored separately rather than as a part of an object. Since they are associated with class itself rather than objects, they are known as class variables. OOPS WITH C++ Sahaj Computer Solutions 17

18 Static Data Members Object A Object B Object C number number number count Common to all three objects OOPS WITH C++ Sahaj Computer Solutions 18

19 Static Member Functions Like static member variables, C++ has static member functions. A member function that is declared as static has following properties: A static function can have access to only other static members (functions or variables) declared in the same class. A static member function can be called using the class name (instead of its object) Syntax: class-name::function-name; Program: Ch4Pg10.cpp OOPS WITH C++ Sahaj Computer Solutions 19

20 Array of Objects Arrays can be of any data type including class and struct. Such variables are called array of objects. Syntax; class-name object-name[size]; Example: employee manager[20]; Program :CH4PG11.cpp OOPS WITH C++ Sahaj Computer Solutions 20

21 Objects as function arguments Like any other data type, an object may be used as a function argument. This can be done in two ways: A copy of the entire object is passed to the function. Only address of the object is transferred to the function. Program: CH4PG12.cpp OOPS WITH C++ Sahaj Computer Solutions 21

22 Friend Functions It is possible to grant a non-member function access to the private members of a class by using a friend. A friend function has access to all private and protected members of the class for which it is a friend. To declare a friend function, include its prototype within the class, preceding it with the keyword friend. Syntax: friend type fn-name(arg-list){ //function body } Program:CH4PG13.cpp OOPS WITH C++ Sahaj Computer Solutions 22

23 Friend Function In this example, the sum() function is not a member of myclass. However, it still has full access to its private members. Also, notice that sum() is called without the use of the dot operator. Because it is not a member function, it does not need to be (indeed,itmay not be) qualified with an object's name. OOPS WITH C++ Sahaj Computer Solutions 23

24 Friend Function A friend function possesses certain special characteristics: It is not in the scope of the class to which it has been declared as friend. Since it is not in the scope of the class, it cannot be called using the object of that class. It can be invoked like normal function without the help of any object. It can be declared in public or private part of the class without affecting its meaning. Usually its has objects as its arguments. OOPS WITH C++ Sahaj Computer Solutions 24

25 A function friendly to two classes Program:CH4PG14.cpp The function max() has arguments from both XYZ and ABC. When the function max() is declared as a friend function in XYZ for the first time, the compiler will not acknowledge the presence of ABC unless its name is declared in the beginning as class ABC; This is known as forward declaration OOPS WITH C++ Sahaj Computer Solutions 25

26 Friend Classes It is possible for one class to be a friend of another class. When this is the case, the friend class and all of its member functions have access to the private members defined within the other class. For example, class Y{ friend class X; }; Program : CH4PG15.cpps OOPS WITH C++ Sahaj Computer Solutions 26

27 Defining Inline Functions Within a Class It is possible to define short functions completely within a class declaration. When a function is defined inside a class declaration, it is automatically made into an inline function (if possible). It is not necessary (but not an error) to precede its declaration with the inline keyword. Program : CH4PG16.cpp OOPS WITH C++ Sahaj Computer Solutions 27

28 Returning Objects A Function can not only receive objects as arguments but also can return them. The following program demonstrates this concept. Program: CH4PG17.cpp OOPS WITH C++ Sahaj Computer Solutions 28

29 Structures and Classes Are Related A class is syntactically similar to a struct. But the relationship between a class and a struct is closer than youmayatfirstthink. In C++, the role of the structure was expanded, making itanalternativewaytospecifyaclass. In fact, theonlydifferencebetween aclassand astruct isthatbydefaultall membersarepublicinastructand private in a class. OOPS WITH C++ Sahaj Computer Solutions 29

30 Unions and Classes Are Related Like a structure, a union may also be used to define a class. In C++, unions may contain both member functions and variables. They may also include constructor and destructor functions. A union in C++ retains all of its C-like features, the most important being that all data elements share the same location in memory. OOPS WITH C++ Sahaj Computer Solutions 30

31 Constructors A constructor is a special member function whose task is to initilize the object of its class. The constructor is invoked whenever the object of the class is created. Syntax: }; class class-name{ public: class-name() //constructor { } Example: class integer{ int x,y; public: integer() { x=0; y=0; } }; OOPS WITH C++ Sahaj Computer Solutions 31

32 Constructors Characteristics of constructors; They should be declared in public section. They have no return type not even void and therefore they do not return values. They cannot be inherited, though derived class constructors can call base class constructor. Constructors cannot be virtual. Program: CH4PG18.cpp OOPS WITH C++ Sahaj Computer Solutions 32

33 Types of constructors There are three types of constructors in C++: Default Constructors Parameterized Constructors Copy constructors Default Constructors: A default constructor is a constructor which does not accept any arguments. OOPS WITH C++ Sahaj Computer Solutions 33

34 Parameterized Constructors A constructor which accepts arguments is called as parameterized constructor. Syntax: class-name :: class-name(argument-list) { } //body of the constructor Example: class integer{ int x,y; public: integer(int a, int b) { x=a; y=b } }; OOPS WITH C++ Sahaj Computer Solutions 34

35 Parameterized Constructors An parameterized constructor can be called using two ways By calling the constructor explicitly By calling the constructor implicitly Examples: integer i=integer(10,20); //explicit call integer i(10,20); //implicit call Program:CH4PG19.CPP OOPS WITH C++ Sahaj Computer Solutions 35

36 Constructor Overloading A class can have one or more than one constructors defined in a class with different number of arguments or different type of arguments. This is called constructor overloading. The compiler recognizes the constructor depending upon the number of arguments or type of arguments. Program: CH4PG OOPS WITH C++ Sahaj Computer Solutions 36

37 Copy Constructor A Constructor which accepts an copy of its own class as an argument is called an copy constructor. Syntax: class-name:: class-name(class-name &obj) { } //constructor body A copy constructor is used to declare and initialize an object from another object. OOPS WITH C++ Sahaj Computer Solutions 37

38 Dynamic Constructor The constructor can also be used to allocate memory while creating objects. This ensures the system to allocate the right amount of memory for each object when the objects are not of the same size, thus resulting in the saving of memory. Allocation of memory to objects at the time of their construction is known as dynamic constructor. OOPS WITH C++ Sahaj Computer Solutions 38

39 Constructors with Default Arguments It is possible to define constructors with default arguments. For example: Complex( float real, float img=0); The argument img=0. Then the statement Complex(5.0); Assigns 5.0 to real and 0 to img (by default) variables. Complex(2.0,3.0); Will assign 2.0 to real part and 3.0 to imgvariables. OOPS WITH C++ Sahaj Computer Solutions 39

40 SahajComputer Solutions Near Gomatesh School, Hindwadi Belgaum-11, Phone no: , Get Certified in Microsoft Office 2010 Tally 9.2.NET 2008 J2EE CORE JAVA C PROGRAMMING OOPS WITH C++ JOOMLA WORDPRESS PHP AND MYSQL SQLSERVER UNIX AND LINUX ANDRIOD APPS Around 1800 students developed software projects and scored the top scores in exams. One stop shop for Software Projects Website Development Technology Training I.T Research Visit: OOPS with C++ Sahaj Computer Solutions 40