Seminar on Simulation of Telecommunication Sistems. Introduction to object-oriented programming: C++

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1 Politecnico di Milano Dipartimento di Elettronica e Informazione Seminar on Simulation of Telecommunication Sistems Introduction to object-oriented programming: C++ Massimo Tornatore Francesco Musumeci (Author of the original slides: Fabio Martignon) 1

2 When C language may cause problems Different programmers working on the same project can use variables with the same names An agreement on data structures to use is necessary A single modification to single parts of the program can cause crashes to the whole system The level of abstraction is constant in the entire program 2

3 Advantages of object-oriented programming It is possible to separate frameworks handled by different programmers by organizing the project in a logical architecture: Sets of logical objects Features of the objects Attributes of the objects which are visible by external functions and portions of the software Methods (functions) to manipulate objects 3

4 Advantages of object-oriented programming Once the names of objects have been defined, there is no ambiguity Functions used to handle objects (member functions) may also have the same names provided they refer to different objects E.g.: function move(x,y) can be used to move more than one kind of objects and can be different according to the object to be moved (though it has the same name move ) 4

5 Advantages of object-oriented programming Variables constituting objects can be: private: can be used only by member functions public: can be used in any portions of the program Operators can be overloaded. Their meaning can be different according to the object. E.g.: Sum of 2 points in the x-y plane: (a,b)+(c,d) Sum of two lists (concatenate the lists) 5

6 Advantages of object-oriented programming inheritance: when an object is created it can inherit the features of another object and add its own polymorphism: different member functions may have the same name but can be different in the way they operate or in the object they handle 6

7 Class declaration class point { private: double x; // abscissa double y; // ordinate public: int id; // identifier }; The word class defines a type of data (it is similar to struct in C language) 7

8 Class declaration The set of variables and methods (functions) is preceded by one of these words: private: For variables or functions which can be used only by member functions (i.e., functions of the same class). It is the default value if no specification is made before variable/function declaration public: For variables or functions which can be used anywhere in the program protected: For variables or functions which can be used by functions of that class or child classes 8

9 Member fuctions class point { private: double x; // abscissa double y; // ordinate public: int id; // identifier prototype of the function void move(double xx, double yy); }; void point::move(double xx, double yy) { x=xx; y=yy; } Body of the function 9

10 Static members The reserved word static, applied to a member, indicates that the member is shared by all the objects of that class In other words, if we use a static variable its value can be modified by one object of the class and the modification is applied to all the objects of that class 10

11 Friend classes and functions Though some variables can be private, it is possible to allow other external entities to use them, thorugh the declaration friend class point { private: double x; // abscissa double y; // ordinate public: friend class topology; int id; // identifier void move(double xx, double yy) }; 11

12 Constructors and destructors Constructors and destructors are special functions (always public) which the program creates automatically when it allocates or deallocates memory for an object C++ allows to use them to execute programmer-defined operations when the object is created or deleted 12

13 Constructors and destructors: example class triangle { protected: point* v1; // vertex 1 point* v2; // vertex 2 point* v3; // vertex 3 public: triangle(); ~triangle(); }; constructor destructor void set_v1(double x, double y); void set_v2(double x, double y); void set_v3(double x, double y); 13

14 Constructors and destructors: example triangle::triangle() { v1=new point(0,0); v2=new point(0,0); v3=new point(0,0); } triangle::~triangle(); delete v1; delete v2; delete v3; } void triangle::set_v1(double x, double y) { v1->move(x,y); } 14

15 Inheritance After defyning a class it is possible to define new classes with the same features and which also add their own properties The first is known as base class (or parent) A class which is derived from it is known as child class From parent to child class, functions and variables: public remains public protected becomes private private are not inherited 15

$Inheritance class colored_triangle: public triangle { private: char* color; public: colored_triangle(); ~colored_triangle(); void$

16 Inheritance class colored_triangle: public triangle { private: char* color; public: colored_triangle(); ~colored_triangle(); void set_color(char* c); char* get_color(); }; void colored_triangle::set_color(char* c){ color=c; } char* colored_triangle::get_color(){ return color; } 16

17 Functions with the same name class point { private: double x; // abscissa double y; // ordinate public: point(double X, double Y); point(); ~point(){}; }; point::point(double X, double Y) { x=x; y=y; } point::point() { x=0.0; y=0.0; } 17

18 Virtual member functions They are preceded by the word virtual in their declaration (base class) They can be re-defined (new body) in a child class keeping the same name: virtual void move(double x, double y); A class is virtual if it has virtual members A function is pure (or abstract) virtual if we set its value to zero: virtual void move(double x, double y)=0; A class which contains at least one abstract virtual function is abstract itself We can define pointers to an abstract class but we can not create object of that type (abstract objects) 18

19 Virtual member functions class object { public: virtual double area()=0; } class triangle : public object { public: virtual double area(); }; class square : public object{ public: virtual double area(); }; 19

20 Virtual member functions If a pointer to an abstract base class is used the pointer can be used to address a (real) object of a child class If a virtual function is used the function which is executed is that of the child class void print_area(object *o) { double aa=o->area(); printf( object area = %f\n, aa); return; } 20

More C++ : Vectors, Classes, Inheritance, Templates

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