Introduction to Object-Oriented Programming in C

1
Introduction to Object-Oriented Programmingin
C

• Vincenzo Innocente
• CERN, Geneva, Switzerland

2
Classes and Objects

• An example of object oriented Programa
  video-game

3
Class Vector

• An example un tri-dimentional vector
• With respect to a structure, a class contains
  functions beside data

constructor
functions or methods
data
copy constructor
4
Class Vector

• How to use Vector

invoke the constructor
5
Class Vector

• Data access protection

6
Interface and implementation

• Protected data are not accessible outside the
  class

Vector.hh
class Vector public Vector(double x, double
y, double z) double x() const double y()
const double z() const double r() const
double phi() const double theta()
const protected double _x, _y, _z
const
Vector.cc
include Vector.h VectorVector(double x,
double y, double z) _x(x), _y(y),
_z(z) double Vectorx() const return _x
double Vectorr() const return sqrt(xx
yy zz)
7
Interface and implementation

• The internal structure of the data (_x, _y, _z)
  that represent the objects of the class Vector
  are hidden (protected) to the clients of the
  class.
• The clients do not depend on the internal
  structure of the data (as it was the case for
  clients of FORTRAN common block)
• If the internal structure changes (es. _r,
  _theta, _phi), the code using Vector does not
  have to be modified.

8
Operators

• It is possible to redefine , -, , , , , .
  . .

9
Operators

• Example

redefinition of ltlt
10
Operators

• Example

p
11
Operator overloading

• It is possible to define functions with the same
  name but different arguments

12
Static Functions and data

• Some functions can be common to the whole class

13
Templates

• The same definition can be applied to different
  types

templateltclass Tgt T sqr(const T x) return x x

templateltclass Tgt T min(const T a, const T b)
return (a lt b ? a b) templateltclass Tgt T
max(const T a, const T b) return (a gt b ? a
b)
recursive
templateltclass Tgt T fact(const T n) return
(n 0 ? 1 n fact(n -
1))
14
Inheritance

• Add methods and attributes to a class

Invoke the constructor of the base class

• Inheritance allows code re-use

15
Inheritance

• A derived class inherits all methods fo the base
  class

• DchTrack is a Track with more attributes (_hits)
  and new methods (DchHit hit(int n), int hits())

16
Abstract Class

• Classic example Shape

• All objets in the window have common behaviors
  which could be considered in abstract
• draw, move, enlarge, etc.

17
Abstract classes and virtual function

• Shape is an abstract class because it has pure
  virtual methods

Pure virtual methods
18
Abstract classes and virtual functions

• Shape clients do not have to know which of its
  derived classes actually implement it.

19
Inheritance

• Careful choosing the correct inheritance
  relations could not be trivial.
• Is a square a rectangle?

• both_lx and _ly are redundant in Square
• What happen if scaleX or scaleY is invoked?

20
Multiple Inheritance

• A class can inherit from more than one class

21
Surfaces and trajectories

• In tracking is often required to compute the
  intersections among curves (tracks) and
  superfaces (detector elements)

Intersection(Surface, Trajectory)
Trajectory
Surface
Line
Helix
PolyLine
Plane
Cylinder
etc . . .
etc . . .
22
Surfaces and trajectories

• Interface of various Trajectorys

23
Surfaces and trajectories

• Implementation

24
Surfaces and trajectories

• Interface of the various Surfaces

distance (with sign) of a point form the surface
25
Surfaces and trajectories

• Surface is an abstract class

scalar product between two Vectors
26
Surfaces and trajectories

• Interface of Intersection

forward class declarations
27
Surfaces and trajectories

• Implementation of the algorithm

28
Surfaces and trajectories

• Intersection uses only
• The methods position and direction of a
  Trajectory object
• The methods distance and derDist of a Surface
  object
• It is possible to add a new class that models a
  new Trajectory or a new Surface and Intersection
  continues to work without modifying a single line
  of code!

29
Shapes Visitors

• Shapes

30
Shapes Visitors

• Visitors

31
Shapes Visitors

• Main

32
Open/Closed principle (R. Martin)

• A good code has to be
• open to extensions
• closed to modifications
• Modifications of a working code can introduce
  defects (bugs)
• Object Orientation, with the mechanism of virtual
  classes, allows to apply this principle