Object-Oriented Programming

Transcription

1 Object-Oriented Programming Section 3: Classes and inheritance (1) Piotr Mielecki, Ph. D.

2 Class vs. structure declaration Inheritance and access specifiers (private, protected, public) Friend methods Friend classes Overloading methods and operators (introduction)

3 Class vs. structure declaration C++ language is the result of evolution of classic C, extended by elements supporting OOP paradigm. Structural struct datatype in C++ can contain both data fields and functions (methods) as its members. The most significant difference between structure and class is using access specifiers (private, protected and public), which make encapsulation of particular members possible.

4 Example 1: Class vs. structure declaration (1) Declaration our header file: #ifndef CLASSES1_H_INCLUDED #define CLASSES1_H_INCLUDED struct Struct1 { int Var1; // Structures in C++ can contain methods. void setvar1(int i); int getvar1(); ; class Class1 { // All class members declared before first manifestly used access specifier // are private (encapsulated) by default. int Var1; // "public" access specifier makes all members of class // declared below accessible from outside. public: void setvar1(int i); int getvar1(); ; #endif // CLASSES1_H_INCLUDED

5 Example 1: Class vs. structure declaration (2) Implementation - our.cpp file: #include "Classes1.h" void Struct1::setVar1(int i) { Var1 = i; int Struct1::getVar1() { return Var1; void Class1::setVar1(int i) { Var1 = i; int Class1::getVar1() { return Var1;

6 Example 1: Class vs. structure declaration (3) Testing - our main.cpp file: #include <iostream> #include "Classes1.h" using namespace std; int main() { Struct1 mystructure; Class1 myclass; mystructure.setvar1(1); cout << "mystructure.var1 = " << mystructure.getvar1() << endl; mystructure.var1 = 2; // This assignment is legal. cout << "mystructure.var1 = " << mystructure.getvar1() << endl; myclass.setvar1(3); cout << "myclass.var1 = " << myclass.getvar1() << endl; // This is illegal: // myclass.var1 = 4; // Var1 is a private member of a Class1 class, so it's not directly // accessible from outside of object of this class type - encapsulation. // Structures don't support encapsulation. return 0;

7 Inheritance and access specifiers (1) General syntax for derived class declaration looks like this: class derived_class : access base1, access base2,... A derived class can directly access all the non-private (that means public and protected) members of its base class (or classes). When deriving a class from a base class, the base class may be inherited through public, protected or private inheritance. Constructors, destructors and assign operator (=) are not inherited from base class to derived class. If we want to use the base class constructor implementing derived class constructor it can be invoked in initializer list, like in this example (see also Example 3 in Section 2): NewClass::NewClass( int xx, int yy, int zz ) : BaseClass( xx, yy ), zz { z = zz;

8 Inheritance and access specifiers (2) When deriving a class from a public base class, public members of the base class become public members of the derived class and protected members of the base class become protected members of the derived class. A private members of base class are never accessible directly from a derived class, but can be accessed through calls to the public and protected members of the base class. When deriving from a protected base class, public and protected members of the base class become protected members of the derived class. When deriving from a private base class, public and protected members of the base class become private members of the derived class.

9 Example 2: Inheritance and access specifiers (1) Declaration our header file (1): #ifndef CLASSES2_H_INCLUDED #define CLASSES2_H_INCLUDED // Problems with constant PI value can occur depending on compiler. #ifndef M_PIl # define M_PIl L #endif // M_PIl // Base class - Point: class Point { // To give the derived class direct access to attributes // we are using "protected" access specifier. protected: double x, y; public: // Constructor with default values: Point(double newx = 0, double newy = 0); ; void setx(double newx); // Setter for x double getx() const; // Getter for x void sety(double newy); // Setter for y double gety() const; // Getter for y void setposition(double newx, double newy);

10 Example 2: Inheritance and access specifiers (2) Declaration our header file (2): // Derived class - Circle: class Circle : public Point { // Maybe someone wants to derive a Cylinder class? protected: double r; public: // Constructor will be not inherited from base class. Circle(double newx = 0, double newy = 0, double newr = 1); void setr(double newr); double getr() const; // Setter for r // Getter for r ; double getarea() const; // A public method which returns area. double getperimeter()const; // A public method which returns perimeter.

11 Example 2: Inheritance and access specifiers (3) Declaration our header file (3): // Derived class - Rectangle: class Rectangle : public Point { // Maybe someone wants to derive a Cuboid class? protected: double a, b; public: // Constructor will be not inherited from base class. Rectangle(double newx = 0, double newy = 0, double newa = 1, double newb = 1); void seta(double newa); double geta() const; void setb(double newa); double getb() const; // Setter for a // Getter for a // Setter for b // Getter for b ; double getarea() const; // A public method which returns area. double getperimeter() const; // A public method which returns perimeter. double getdiagonal() const; // A public method which returns diagonal. #endif // CLASSES2_H_INCLUDED

12 Example 2: Inheritance and access specifiers (4) Implementation our.cpp file (1): #include "Classes2.h" #include <math.h> Point::Point(double newx, double newy) { x = newx; y = newy; void Point::setX(double newx) { x = newx; double Point::getX(void) const { return x; void Point::setY(double newy) { y = newy; double Point::getY(void) const { return y; void Point::setPosition(double newx, double newy) { x = newx; y = newy;

13 Example 2: Inheritance and access specifiers (4) Implementation our.cpp file (2): Circle::Circle(double newx, double newy, double newr) { x = newx; y = newy; setr(newr); // Constructor can call class methods without prefix. void Circle::setR(double newr) { r = newr >= 0? newr : -1 * newr; double Circle::getR() const { return r; double Circle::getArea() const { return M_PIl * r * r; double Circle::getPerimeter() const { return 2 * M_PIl * r;

14 Example 2: Inheritance and access specifiers (5) Implementation our.cpp file (3): Rectangle::Rectangle(double newx, double newy, double newa, double newb) { x = newx; y = newy; seta(newa); setb(newb); void Rectangle::setA(double newa) { a = newa >= 0? newa : -1 * newa; double Rectangle::getA() const { return a; void Rectangle::setB(double newb) { b = newb >= 0? newb : -1 * newb; double Rectangle::getB() const { return b;

15 Example 2: Inheritance and access specifiers (6) Implementation our.cpp file (4): double Rectangle::getArea() const { return a * b; double Rectangle::getPerimeter() const { return 2 * a + 2 * b; double Rectangle::getDiagonal() const { return sqrt(a * a + b * b);

16 Example 2: Inheritance and access specifiers (7) Testing - our main.cpp file (1): #include <iostream> #include "Classes2.h" using namespace std; int main() { Circle mycircle1; Circle mycircle2(10, 10, 10); Rectangle myrectangle(30, 30, 10, 20); cout << "mycircle1: " << endl; cout << "x = " << mycircle1.getx(); cout << ", y = " << mycircle1.gety(); cout << ", r = " << mycircle1.getr(); cout << ", Area = " << mycircle1.getarea(); cout << ", Perimeter = " << mycircle1.getperimeter() << endl; cout << "mycircle2: " << endl; cout << "x = " << mycircle2.getx(); cout << ", y = " << mycircle2.gety(); cout << ", r = " << mycircle2.getr(); cout << ", Area = " << mycircle2.getarea(); cout << ", Perimeter = " << mycircle2.getperimeter() << endl;

17 Example 2: Inheritance and access specifiers (8) Testing - our main.cpp file (2): cout << "myrectangle:" << endl; cout << "x = " << myrectangle.getx(); cout << ", y = " << myrectangle.gety(); cout << ", a = " << myrectangle.geta(); cout << ", b = " << myrectangle.getb(); cout << ", Area = " << myrectangle.getarea(); cout << ", Perimeter = " << myrectangle.getperimeter(); cout << ", Diagonal = " << myrectangle.getdiagonal() << endl; return 0;

18 Friend methods When declaring a class its author can give a direct access to all its members (public, protected and private) for functions (methods) form outside of the class. Prototypes for those methods are declared inside the class declaration and prefixed with friend keyword. Friend function can be implemented in any other module of program, by other member of developers team for example. In fact we can say that friend function is kind of backdoor to the class overcomes the access specifiers. That s why the key (friend method declaration inside the class) is kept by author of the class.

19 Example 3: Friend functions (1) Declaration our Point.h header file for Point class (1): #ifndef POINT_H_INCLUDED #define POINT_H_INCLUDED // Those 2 declarations are "promising" classes used by friend // functions but not declared in this file. class Circle; // Forward declaration of Circle class class Rectangle; // Forward declaration of Rectangle class // Base class - Point: class Point { // To give the derived class direct access to attributes // we are using "protected" access specifier. protected: double x, y; public: // Constructor with default values: Point(double newx = 0, double newy = 0); void setx(double newx); // Setter for x double getx() const; // Getter for x void sety(double newy); // Setter for y double gety() const; // Getter for y void setposition(double newx, double newy);

20 Example 3: Friend functions (2) Declaration our Point.h header file for Point class (2): // Compiler knows about Circle and Rectangle classes // because of forward declarations. // So we can declare two overloaded functions which are // detecting if point is inside the circle or rectangle // this way: friend bool pointinshape(point pnt, Circle circ); friend bool pointinshape(point pnt, Rectangle rect);; // We can add functions for console interface also as "friend" ones: friend std::ostream &operator << (std::ostream &os, Point &pnt); friend std::istream &operator >> (std::istream &is, Point &pnt); #endif // POINT_H_INCLUDED

21 Declaration our Circle.h header file for Circle class (1): #ifndef CIRCLE_H_INCLUDED #define CIRCLE_H_INCLUDED #include "Point.h" Example 3: Friend functions (3) // Problems with constant PI value can occur depending on compiler. #ifndef M_PIl # define M_PIl L #endif // M_PIl // Class derived form Point - Circle: class Circle : public Point { // Maybe someone wants to derive a Cylinder class? protected: double r; public: // Constructor will be not inherited from base class. Circle(double newx = 0, double newy = 0, double newr = 1); void setr(double newr); double getr() const; // Setter for r // Getter for r

22 Example 3: Friend functions (4) Declaration our Circle.h header file for Circle class (2): double getarea() const; // A public method which returns area. double getperimeter()const; // A public method which returns perimeter. friend bool pointinshape(point pnt, Circle circ); ; friend std::ostream &operator << (std::ostream &os, Circle &circ); friend std::istream &operator >> (std::istream &is, Circle &circ); #endif // CIRCLE_H_INCLUDED

23 Declaration our Rectangle.h header file for Rectangle class (1): #ifndef RECTANGLE_H_INCLUDED #define RECTANGLE_H_INCLUDED #include "Point.h" Example 3: Friend functions (5) // Class derived from Point - Rectangle: class Rectangle : public Point { // Maybe someone wants to derive a Cuboid class? protected: double a, b; public: // Constructor will be not inherited from base class. Rectangle(double newx = 0, double newy = 0, double newa = 1, double newb = 1); void seta(double newa); double geta() const; void setb(double newa); double getb() const; // Setter for a // Getter for a // Setter for b // Getter for b

24 Example 3: Friend functions (6) Declaration our Rectangle.h header file for Rectangle class (2): double getarea() const; double getperimeter() const; double getdiagonal() const; // A public method which returns area. // A public method which returns perimeter. // A public method which returns diagonal. friend bool pointinshape(point pnt, Rectangle rect); ; friend std::ostream &operator << (std::ostream &os, Rectangle &rect); friend std::istream &operator >> (std::istream &is, Rectangle &rect); #endif // RECTANGLE_H_INCLUDED

25 Implementation our Point.cpp file for Point class: #include "Point.h" Example 3: Friend functions (7) Point::Point(double newx, double newy) { x = newx; y = newy; void Point::setX(double newx) { x = newx; double Point::getX() const { return x; void Point::setY(double newy) { y = newy; double Point::getY() const { return y; void Point::setPosition(double newx, double newy) { x = newx; y = newy;

26 Example 3: Friend functions (8) Implementation our Circle.cpp file for Circle class: #define _USE_MATH_DEFINES #include <math.h> #include "Circle.h" Circle::Circle(double newx, double newy, double newr) { x = newx; y = newy; setr( newr ); void Circle::setR(double newr) { r = newr >= 0? newr : -1 * newr; double Circle::getR() const { return r; double Circle::getArea() const { return M_PIl * r * r; double Circle::getPerimeter() const { return 2 * M_PIl * r;

27 Example 3: Friend functions (9) Implementation our Rectangle.cpp file for Rectangle class (1): #include <math.h> #include "Rectangle.h" Rectangle::Rectangle(double newx, double newy, double newa, double newb) { x = newx; y = newy; seta(newa); setb(newb); void Rectangle::setA(double newa) { a = newa >= 0? newa : -1 * newa; double Rectangle::getA() const { return a; void Rectangle::setB(double newb) { b = newb >= 0? newb : -1 * newb; double Rectangle::getB() const { return b;

28 Example 3: Friend functions (10) Implementation our Rectangle.cpp file for Rectangle class (2): double Rectangle::getArea() const { return a * b; double Rectangle::getPerimeter() const { return 2 * a + 2 * b; double Rectangle::getDiagonal() const { return sqrt( a * a + b * b );

29 Example 3: Friend functions (11) Implementation our Friends.cpp file for friend functions (1): // Overloaded functions for detecting if given point is inside the object. // For Circle class: bool pointinshape(point pnt, Circle circ) { if( (pnt.x - circ.x)*(pnt.x - circ.x) + (pnt.y - circ.y)*(pnt.y - circ.y) \ <= circ.r * circ.r ) return true; else return false; // For Rectangle class: bool pointinshape(point pnt, Rectangle rect) { if( (pnt.x >= rect.x) && (pnt.x <= rect.x + rect.a) && \ (pnt.y >= rect.y) && (pnt.y <= rect.y + rect.b) ) return true; else return false;

30 Example 3: Friend functions (12) Implementation our Friends.cpp file for friend functions (2): // Functions supporting console interface ("views") by overloading // the << and >> operators. // For Point class: std::ostream &operator << (std::ostream &os, Point &pnt) { return std::cout << "x = " << pnt.x << ", y = " << pnt.y; std::istream &operator >> (std::istream &is, Point &pnt) { return std::cin >> pnt.x >> pnt.y; // For Circle class: std::ostream &operator << (std::ostream &os, Circle &circ) { return std::cout << "x = " << circ.x << ", y = " << circ.y << \ ", r = " << circ.r; std::istream &operator >> (std::istream &is, Circle &circ) { return std::cin >> circ.x >> circ.y >> circ.r; // For Rectangle class: std::ostream &operator << (std::ostream &os, Rectangle &rect) { return std::cout << "x = " << rect.x << ", y = " << rect.y << \ ", a = " << rect.a << ", b = " << rect.b; std::istream &operator >> (std::istream &is, Rectangle &rect) { return std::cin >> rect.x >> rect.y >> rect.a >> rect.b;

31 Example 3: Friend functions (13) Testing our main.cpp file for main segment (1): #include <iostream> #include "Point.h" #include "Circle.h" #include "Rectangle.h" using namespace std; int main() { Point mypoint; Circle mycircle; Rectangle myrectangle; string choice;

32 Example 3: Friend functions (14) Testing our main.cpp file for main segment (2): // Program control loop: do { // We are using user interface ("view") on standard text console // implemented as appropriate friend functions, which are overloading // << and >> operators of C++ iostream for Point, Circle and Rectangle // classes. cout << "mypoint: enter x and y (separated with space): "; cin >> mypoint; cout << "mypoint: " << mypoint << endl; cout << "mycircle: enter x, y and r (separated with spaces): "; cin >> mycircle; cout << "mycircle: " << mycircle << endl; cout << "myrectangle: enter x, y, a and b (separated with spaces): "; cin >> myrectangle; cout << "myrectangle: " << myrectangle << endl;

33 Example 3: Friend functions (15) Testing our main.cpp file for main segment (3): // This time object attributes are read by getters (this still works, of course): cout << endl << "Objects:" << endl; cout << "mypoint: x = " << mypoint.getx() << ", y = " << mypoint.gety() << endl; cout << "mycircle: x = " << mycircle.getx() << ", y = " << mycircle.gety(); cout << ", r = " << mycircle.getr() << endl; cout << "myrectangle: x = " << myrectangle.getx() << ", y = " \ << myrectangle.gety(); cout << ", a = " << myrectangle.geta() << ", b = " << myrectangle.getb() << endl; if( pointinshape(mypoint, mycircle) ) cout << "mypoint is inside the mycircle." << endl; else cout << "mypoint is outside the mycircle." << endl; if( pointinshape(mypoint, myrectangle) ) cout << "mypoint is inside the myrectangle." << endl; else cout << "mypoint is outside the myrectangle." << endl; cout << endl << "Do you want to set new values (Y/N)? "; cin >> choice; while( choice == "Y" choice == "y" ); return 0;

34 Example 3: Friend functions (16) Testing screenshot: Picture above shows results from running program.

35 Example 3: Friend functions (summary) In this example functions declared as friend ones have direct access to all attributes and methods of classes, although this access is granted in declarations of classes. Friend functions are not the members of classes, they can only work with objects of those classes from outside. Implementing the access (user interface) in friend functions (overloading of << and >> operators in this example) separates this interface from classes themselves. Author of the class only specifies way in which particular kind of user interface (standard text console in this case, but something like this can be specified for Windows controls, HTML tags etc.) can interact with object of this class. In well organized project we should clearly separate the user interface (collection of views Windows or X Window forms, HTML pages etc.) and code of application itself (data model, algorithms, communication interface etc.).

36 Friend classes Instead of giving direct access to all members of the class for particular functions, author can declare the friend class. Friend class (or classes) can also be implemented in any other module of program, by other member of developers team for example (it s a matter of trust). Author of the classes which accept friend class declares only the name of this friend class doesn t need to declare prototypes for particular functions / methods. The modifications in code from Example 3 are shown in next example. This time project is clearly arranged data model (Point, Circle and Rectangle classes), supported with some extra processing in DataFriends class is separated from user interface (view) supported by ViewFriends class. In this example ViewFriends class supports text console interface. In other project it can support controls available in Windows GUI, HTML etc. Only this class (and main segment) will be implemented in different way then.

37 Declaration our header file for Point class (1): #ifndef POINT_H_INCLUDED #define POINT_H_INCLUDED Example 4: Friend classes (1) // Forward declarations of friend or derived classes are not necessary. // Base class - Point: class Point { // To give the derived class direct access to attributes // we are using "protected" access specifier. protected: double x, y; public: // Constructor with default values: Point(double newx = 0, double newy = 0); void setx(double newx); // Setter for x double getx() const; // Getter for x void sety(double newy); // Setter for y double gety() const; // Getter for y void setposition(double newx, double newy);

38 Example 4: Friend classes (2) Declaration our header file for Point class (2): ; friend class DataFriends; friend class ViewFriends; #endif // POINT_H_INCLUDED

39 Declaration our header file for Circle class (1): #ifndef CIRCLE_H_INCLUDED #define CIRCLE_H_INCLUDED #include "Point.h" Example 4: Friend classes (3) // Problems with constant PI value can occur depending on compiler. #ifndef M_PIl # define M_PIl L #endif // M_PIl // Class derived form Point - Circle: class Circle : public Point { // Maybe someone wants to derive a Cylinder class? protected: double r; public: // Constructor will be not inherited from base class. Circle(double newx = 0, double newy = 0, double newr = 1); void setr(double newr); double getr() const; // Setter for r // Getter for r

40 Example 4: Friend classes (4) Declaration our header file for Circle class (2): double getarea() const; // A public method which returns area. double getperimeter()const; // A public method which returns perimeter. ; friend class DataFriends; friend class ViewFriends; #endif // CIRCLE_H_INCLUDED

41 Declaration our header file for Rectangle class (1): #ifndef RECTANGLE_H_INCLUDED #define RECTANGLE_H_INCLUDED #include "Point.h" Example 4: Friend classes (5) // Class derived from Point - Rectangle: class Rectangle : public Point { // Maybe someone wants to derive a Cuboid class? protected: double a, b; public: // Constructor will be not inherited from base class. Rectangle(double newx = 0, double newy = 0, double newa = 1, double newb = 1); void seta(double newa); double geta() const; void setb(double newb); double getb() const; // Setter for a // Getter for a // Setter for b // Getter for b

42 Example 4: Friend classes (6) Declaration our header file for Rectangle class (2): double getarea() const; double getperimeter() const; double getdiagonal() const; // A public method which returns area. // A public method which returns perimeter. // A public method which returns diagonal. ; friend class DataFriends; friend class ViewFriends; #endif // RECTANGLE_H_INCLUDED

43 Declaration our header file for DataFriends class (1): #ifndef DATAFRIENDS_H_INCLUDED #define DATAFRIENDS_H_INCLUDED #include "Point.h" #include "Circle.h" #include "Rectangle.h" Example 4: Friend classes (7) class DataFriends { public: // Overloaded methods for detecting if given point is inside the shape. // For Circle: bool pointinshape(point pnt, Circle circ); // For Rectangle: bool pointinshape(point pnt, Rectangle rect);

44 Example 4: Friend classes (8) Declaration our header file for DataFriends class (2): // Methods for quick setting attributes of shapes (maybe someone needs them). // Object must be passed to function by pointer - then function works // on object itself, not on its copy. // In this case methods are not overloaded as setshape() for example, // but of course we can do it. ; // Method which sets all attributes of the Circle class object. void setcircle(circle *cr, double newx, double newy, double newr); // Method which sets all attributes of the Rectangle class object. void setrectangle(rectangle *rt, double newx, double newy, double newa, double newb); #endif // DATAFRIENDS_H_INCLUDED

45 Example 4: Friend classes (9) Declaration our header file for ViewFriends class: #ifndef VIEWFRIENDS_H_INCLUDED #define VIEWFRIENDS_H_INCLUDED #include "Point.h" #include "Circle.h" #include "Rectangle.h" class ViewFriends { public: // Overloaded methods supporting console interface ("views"). // For Point class: void viewinput(point *pnt); void viewoutput(point pnt); void viewfullinfo(point pnt); // For Circle class: void viewinput(circle *circ); void viewoutput(circle circ); void viewfullinfo(circle circ); // For Rectangle class: void viewinput(rectangle *rect); void viewoutput(rectangle rect); void viewfullinfo(rectangle rect); ; #endif // VIEWFRIENDS_H_INCLUDED

46 Implementation our.cpp file for Point class: #include "Point.h" Example 4: Friend classes (10) Point::Point(double newx, double newy) { x = newx; y = newy; void Point::setX(double newx) { x = newx; double Point::getX() const { return x; void Point::setY(double newy) { y = newy; double Point::getY() const { return y; void Point::setPosition(double newx, double newy) { x = newx; y = newy;

47 Implementation our.cpp file for Circle class: #include <math.h> #include "Circle.h" Example 4: Friend classes (11) Circle::Circle(double newx, double newy, double newr) { x = newx; y = newy; setr(newr); void Circle::setR(double newr) { r = newr >= 0? newr : -1 * newr; double Circle::getR() const { return r; double Circle::getArea() const { return M_PIl * r * r; double Circle::getPerimeter() const { return 2 * M_PIl * r;

48 Implementation our.cpp file for Rectangle class (1): #include <math.h> #include "Rectangle.h" Example 4: Friend classes (12) Rectangle::Rectangle(double newx, double newy, double newa, double newb) { x = newx; y = newy; seta(newa); setb(newb); void Rectangle::setA(double newa) { a = newa >= 0? newa : -1 * newa; double Rectangle::getA() const { return a; void Rectangle::setB(double newb) { b = newb >= 0? newb : -1 * newb; double Rectangle::getB() const { return b;

49 Example 4: Friend classes (13) Implementation our.cpp file for Rectangle class (2): double Rectangle::getArea() const { return a * b; double Rectangle::getPerimeter() const { return 2 * a + 2 * b; double Rectangle::getDiagonal() const { return sqrt(a * a + b * b);

50 Implementation our.cpp file for DataFriends class (1): #include "DataFriends.h" Example 4: Friend classes (14) bool DataFriends::pointInShape(Point pnt, Circle circ) { if( (pnt.x - circ.x)*(pnt.x - circ.x) + (pnt.y - circ.y)*(pnt.y - circ.y)\ <= circ.r * circ.r ) return true; else return false; bool DataFriends::pointInShape(Point pnt, Rectangle rect) { if( (pnt.x >= rect.x)&&(pnt.x <= rect.x + rect.a) \ &&(pnt.y >= rect.y)&&(pnt.y <= rect.y + rect.b) ) return true; else return false;

51 Example 4: Friend classes (15) Implementation our.cpp file for DataFriends class (2): void DataFriends::setCircle(Circle *cr, double newx, double newy, double newr) { cr->x = newx; cr->y = newy; cr->r = newr; void DataFriends::setRectangle(Rectangle *rt, double newx, double newy, double newa, double newb) { rt->x = newx; rt->y = newy; rt->a = newa; rt->b = newb;

52 Example 4: Friend classes (16) Implementation our.cpp file for ViewFriends class (1): #include <iostream> #include "ViewFriends.h" void ViewFriends::viewInput(Point *pnt) { std::cin >> pnt->x >> pnt->y; void ViewFriends::viewOutput(Point pnt) { std::cout << "Point: x = " << pnt.x << ", y = " << pnt.y << std::endl; void ViewFriends::viewFullInfo(Point pnt) { std::cout << "Point: x = " << pnt.x << ", y = " << pnt.y << std::endl; void ViewFriends::viewInput(Circle *circ) { std::cin >> circ->x >> circ->y >> circ->r; void ViewFriends::viewOutput(Circle circ) { std::cout << "Circle: x = " << circ.x << ", y = " << circ.y << ", r = " \ << circ.r << std::endl; void ViewFriends::viewFullInfo(Circle circ) { std::cout << "Circle: x = " << circ.x << ", y = " << circ.y << ", r = " \ << circ.r << std::endl; std::cout << " area = " << circ.getarea() << ", perimeter = " \ << circ.getperimeter() << std::endl;

53 Example 4: Friend classes (17) Implementation our.cpp file for ViewFriends class (2): void ViewFriends::viewInput(Rectangle *rect) { std::cin >> rect->x >> rect->y >> rect->a >> rect->b; void ViewFriends::viewOutput(Rectangle rect) { std::cout << "Rectangle: x = " << rect.x << ", y = " << rect.y << ", a = " \ << rect.a << ", b = " << rect.b << std::endl; void ViewFriends::viewFullInfo(Rectangle rect) { std::cout << "Rectangle: x = " << rect.x << ", y = " << rect.y << ", a = " \ << rect.a << ", b = " << rect.b << std::endl; std::cout << " area = " << rect.getarea() << ", perimeter = " \ << rect.getperimeter() << rect.getperimeter() << ", diagonal = " \ << rect.getdiagonal() << std::endl;

54 Testing our.cpp file for main segment (1): #include <iostream> #include "Point.h" #include "Circle.h" #include "Rectangle.h" #include "DataFriends.h" #include "ViewFriends.h" using namespace std; Example 4: Friend classes (18) int main() { Point mypoint; Circle mycircle; Rectangle myrectangle; DataFriends mydatafriends; ViewFriends myviewfriends; string choice;

55 Example 4: Friend classes (19) Testing our.cpp file for main segment (2): // Program control loop: do { cout << "mypoint: enter x and y (separated with space): "; myviewfriends.viewinput(&mypoint); myviewfriends.viewoutput(mypoint); cout << "mycircle: enter x, y and r (separated with spaces): "; myviewfriends.viewinput(&mycircle); myviewfriends.viewoutput(mycircle); cout << "myrectangle: enter x, y, a and b (separated with spaces): "; myviewfriends.viewinput(&myrectangle); myviewfriends.viewoutput(myrectangle);

56 Example 4: Friend classes (20) Testing our.cpp file for main segment (3): cout << endl << "Objects:" << endl; myviewfriends.viewfullinfo(mypoint); myviewfriends.viewfullinfo(mycircle); myviewfriends.viewfullinfo(myrectangle); if( mydatafriends.pointinshape(mypoint, mycircle) ) cout << "mypoint is inside the mycircle." << endl; else cout << "mypoint is outside the mycircle." << endl; if( mydatafriends.pointinshape(mypoint, myrectangle) ) cout << "mypoint is inside the myrectangle." << endl; else cout << "mypoint is outside the myrectangle." << endl; cout << endl << "Do you want to set new values (Y/N)? "; cin >> choice; while( choice == "Y" choice == "y" ); return 0;

57 Example 4: Friend classes (summary) Solution shown in this example is more elegant than this from Example 3. First of all main segment can be implemented as user interface only (organizing views) in fact we don t need to use here methods other than supported by ViewFriends class, designed exactly for this purpose. Class DataFriends helps us to perform some processing with data (acquired by user interface, for example), but it doesn t depend on this interface (will be the same for GUI applications, for other system platforms etc.). The same is true about all methods available for Point, Circle and Rectangle classes we don t need to modify them in other projects. Friend classes are very powerful as technique for implementing this kind of interface, but they have one important disadvantage they are by-passing the security means given by encapsulation (private access to some attributes and methods). So we should use this technique very carefully.

58 Overloading methods and operators (introduction) In last two examples (3 and 4) overloading of some methods (and operator functions) was introduced in advance. It will be explained deeper in Section 4. Overloading helps to create code more transparent than using numerous methods with different names, although compiler still has to generate different versions of functions and insert them to executable code not all of them will be used. More optimal and efficient code (limited to methods used in particular context) is generated when we are using techniques like virtual inheritance and polymorphism or templates (will be explained in next sections). Overloading of operators gives the same benefits and issues, as overloading of normal methods. Next example (Example 5) shows implementation of basic operations on 2-dimensional vectors (useful for solving mechanical problems, for example). Operators like ==,!=, =, and + are overloaded.

59 Data model definition of the Vector2D class in header file (1): #ifndef VECTOR2D_H_INCLUDED #define VECTOR2D_H_INCLUDED Example 5: Class with overloaded operators Vector2D (1) #include "Point.h" // Base Point class (nearly the same as in previous examples) #include <math.h> // Problems with constant PI value can occur depending on compiler. #ifndef M_PIl # define M_PIl L #endif // M_PIl // Class derived form Point - Vector2D: class Vector2D : public Point { protected: double l; // Length of vector (module) [mm] double alpha; // Angle to X-axis [deg] public: // Constructor will be not inherited from base class. Vector2D(double newx = 0, double newy = 0, double newl = 0, double newa = 0); void setlength(double newl); double getlength() const; void setangle(double newa); double getangle() const; // Setter for l // Getter for l // Setter for alpha (input in [deg]) // Getter for alpha (return in [deg])

60 Example 5: Class with overloaded operators Vector2D (2) Data model definition of the Vector2D class in header file (2): double getcompx() const; double getcompy() const; // A public method which returns component X // A public method which returns component Y // Four overloaded operators: equal, not equal, assignment and addition: bool operator ==(const Vector2D v2); bool operator!=(const Vector2D v2); void operator =(const Vector2D v2); Vector2D operator +(const Vector2D v2); ; // Friend class supporting views for text console: friend class ViewFriends; #endif // VECTOR2D_H_INCLUDED

61 Data model definition of the base Point class in header file: #ifndef POINT_H_INCLUDED #define POINT_H_INCLUDED Example 5: Class with overloaded operators Vector2D (3) // Base class - Point: class Point { // To give the derived class direct access to attributes // we are using "protected" access specifier. protected: double x, y; public: // Constructor with default values: Point(double newx = 0, double newy = 0); void setx(double newx); // Setter for x double getx() const; // Getter for x void sety(double newy); // Setter for y double gety() const; // Getter for y void setposition(double newx, double newy); ; friend class ViewFriends; // In this case we need only one friend class. #endif // POINT_H_INCLUDED

62 Data model implementation of the base Point class in.cpp file: #include "Point.h" Example 5: Class with overloaded operators Vector2D (4) Point::Point(double newx, double newy) { x = newx; y = newy; void Point::setX(double newx) { x = newx; double Point::getX() const { return x; void Point::setY(double newy) { y = newy; double Point::getY() const { return y; void Point::setPosition(double newx, double newy) { x = newx; y = newy;

63 Data model implementation of the Vector2D class in.cpp file (1): #include <math.h> #include "Vector2D.h" Example 5: Class with overloaded operators Vector2D (5) Vector2D::Vector2D(double newx, double newy, double newl, double newa) { x = newx; y = newy; setlength(newl); setangle(newa); void Vector2D::setLength(double newl) { l = newl >= 0? newl : -1 * newl; double Vector2D::getLength() const { return l; void Vector2D::setAngle(double newa) { while( sqrt(newa * newa) >= 360 ){ newa = newa > 0? newa : newa + 360; alpha = newa; double Vector2D::getAngle() const { return alpha;

64 Example 5: Class with overloaded operators Vector2D (6) Data model implementation of the Vector2D class in.cpp file (2): double Vector2D::getCompX() const { return l * cos(alpha * M_PIl / 180); double Vector2D::getCompY() const { return l * sin(alpha * M_PIl / 180); bool Vector2D::operator ==(const Vector2D v2) { if( x == v2.x && y == v2.y && l == v2.l && alpha == v2.alpha ) return true; else return false; bool Vector2D::operator!=(const Vector2D v2) { if( x!= v2.x y!= v2.y l!= v2.l alpha!= v2.alpha ) return true; else return false;

65 Example 5: Class with overloaded operators Vector2D (7) Data model implementation of the Vector2D class in.cpp file (3): void Vector2D::operator =(const Vector2D v2) { // Pointer "this" is not necessary //this->x = v2.x; //this->y = v2.y; //this->l = v2.l; //this->alpha = v2.alpha; x = v2.x; y = v2.y; l = v2.l; alpha = v2.alpha;

66 Example 5: Class with overloaded operators Vector2D (8) Data model implementation of the Vector2D class in.cpp file (4): Vector2D Vector2D::operator +(const Vector2D v2) { double dx, dy, dl, beta; if( x!= v2.x y!= v2.y ) // Vectors have different points of application, // so we can't add them - return first one. return Vector2D(x, y, l, alpha); else { dx = getcompx() + v2.getcompx(); dy = getcompy() + v2.getcompy(); dl = sqrt(dx * dx + dy * dy); beta = atan(dy / dx); return Vector2D(x, y, dl, beta * 180 / M_PIl);

67 Views definition of the ViewFriends class in header file: #ifndef VIEWFRIENDS_H_INCLUDED #define VIEWFRIENDS_H_INCLUDED #include "Point.h" #include "Vector2D.h" Example 5: Class with overloaded operators Vector2D (9) class ViewFriends { public: // Overloaded methods supporting console interface ("views"). // For Point class: void viewinput(point *pnt); void viewoutput(point pnt); void viewfullinfo(point pnt); // For Vector2D class: void viewinput(vector2d *vct); void viewoutput(vector2d vct); void viewfullinfo(vector2d vct); ; #endif // VIEWFRIENDS_H_INCLUDED

68 Views implementation of the ViewFriends class in.cpp file (1): #include <iostream> #include "ViewFriends.h" Example 5: Class with overloaded operators Vector2D (10) void ViewFriends::viewInput(Point *pnt) { std::cin >> pnt->x >> pnt->y; void ViewFriends::viewOutput(Point pnt) { std::cout << "Point: x = " << pnt.x << ", y = " << pnt.y << std::endl; void ViewFriends::viewFullInfo(Point pnt) { std::cout << "Point: x = " << pnt.x << ", y = " << pnt.y << std::endl; void ViewFriends::viewInput(Vector2D *vct) { double newl, newa; std::cin >> vct->x >> vct->y >> newl >> newa; vct->setlength(newl); vct->setangle(newa); void ViewFriends::viewOutput(Vector2D vct) { std::cout << "Vector2D: x = " << vct.x << ", y = " << vct.y \ << ", length = " << vct.l << ", angle = " << vct.alpha << std::endl;

69 Example 5: Class with overloaded operators Vector2D (11) Views implementation of the ViewFriends class in.cpp file (2): void ViewFriends::viewFullInfo(Vector2D vct) { std::cout << "Vector2D: x = " << vct.x << ", y = " << vct.y \ << ", length = " << vct.l << ", angle = " << vct.alpha << std::endl; std::cout << " comp. X = " << vct.getcompx() \ << ", comp. Y = " << vct.getcompy() << std::endl;

70 Testing our main.cpp file (1): #include <iostream> #include "Vector2D.h" #include "ViewFriends.h" using namespace std; Example 5: Class with overloaded operators Vector2D (12) int main() { Vector2D myvectors[4]; ViewFriends myviewfriends; int i, j; string choice; // Program control loop: do { cout << "myvectors[0]: enter x, y, length and angle (separated with spaces): "; myviewfriends.viewinput(&myvectors[0]); myviewfriends.viewoutput(myvectors[0]); cout << "myvectors[1]: enter x, y, length and angle (separated with spaces): "; myviewfriends.viewinput(&myvectors[1]); myviewfriends.viewoutput(myvectors[1]);

71 Example 5: Class with overloaded operators Vector2D (13) Testing our main.cpp file (2): myvectors[2] = myvectors[0]; myvectors[3] = myvectors[0] + myvectors[1]; for( i = 0; i < 4; i++ ) { cout << endl << "myvectors[" << i << "]" << endl; myviewfriends.viewfullinfo(myvectors[i]); cout << endl; for( i = 0; i < 4; i++ ) { for( j = i+1; j < 4; j++ ) { if( myvectors[i] == myvectors[j] ) cout << "myvectors[" << i << "] == myvectors[" << j << "]" << endl; cout << endl << "Do you want to set new values (Y/N)? "; cin >> choice; while( choice == "Y" choice == "y" ); return 0;

72 Example 5: Class with overloaded operators Vector2D (14) Testing screenshot: Picture above shows results from running program. Please consider limited accuracy of calculations (myvectors[1]). Double float (64-bit) numbers were used, but some error of approximation exists (about for this particular value).