Kỹ thuật lập trình hệ cơ điện tử= programming engineering in mechatronics chapter iii object oriented programming in c++

➢ The class body is enclosed within curly brackets followed by a semi-colon ➔ contain the data members, member functions, and the keywords regulating access to the members and followed b

KỸ THUẬT LẬP TRÌNH HỆ CƠ ĐIỆN TỬ Programming Engineering in Mechatronics

1

Giảng viên: TS Nguyễn Thành Hùng Đơn vị: Bộ môn Cơ điện tử, Viện Cơ khí

Hà Nội, 2020

❖ Basic principles

❖ An object-oriented example code

▪ Class

• A class determines the abstract features of a object, including its

features (attributes, fields, properties) and its behaviour (what the thing can do, methods, operations and functions)

• We can say that a class is a scheme describing the nature of

something

• Both the integrated properties and the methods of a class are

called class members

▪ Object

• An object is a scheme (an example) of a class

▪ Instance

• Instance means an actual object created at runtime: myCar is an

instance of the class Truck.

• The set of the property values of the actual object is called

the state of that object.

▪ Method

• Methods are responsible for the capabilities of objects: the

methods of myCar: Brake(), Ignition(),

• In C++, methods are rather called member functions.

▪ Message passing

• Message passing is the process during which an object sends

data to another object or "asks" another object to execute one

of its methods

• On the code level, message passing is realised by calling a

method in C++

❖ Basic principles

❖ An object-oriented example code

▪ Encapsulation, data hiding

• Classes principally consist of features (state) and methods

(behaviour).

• There are some features and methods that we hide from other

objects These are internal (private or protected) states and

behaviour

• However, the others are made public.

• According to the basic principles of OOP, the state features have

to be private while most of the methods may be public.

▪ Inheritance

• Inheritance means creating specific versions of a class that inherit the

features and behaviour of their parent class (base class) and use them as if

they were of their own The classes created in this way are called subclasses

or derived classes.

Inheritance

▪ Inheritance

• Actually, inheritance is an is-a relation: myCar is a HeavyTruck,

a HeavyTruck is a Truck So myCar has the methods of both

HeavyTruck and Truck.

• Both derived classes have one direct parent class, namely Truck

This inheritance method is called single inheritance.

members of more direct parent classes

▪ Inheritance

Multiple inheritance

▪ Abstraction

• Abstraction simplifies complex reality by modelling problems

with their corresponding classes and it has its effects on the level

of inheritance appropriate for these problems

• Abstraction can be achieved through composition

• An interface determines how to send element or receive from

element messages and it gives information about the interaction between the components of the class

▪ Abstraction

▪ Polymorphism

• Polymorphism makes it possible to replace the content of some

inherited (deprecated) behaviour forms (methods) with a new

one in the derived class and to treat the new, replaced methods

as the members of the parent class

❖ Basic principles

❖ An object-oriented example code

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➢ The header of the class contains the keyword class/struct,

followed by the name of the class

➢ The class body is enclosed within curly brackets followed by a

semi-colon ➔ contain the data members, member functions, and the keywords regulating access to the members and followed by a

colon: public, private (hidden) and protected.

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❖ More about classes

❖ Operator overloading

▪ A little revision

▪ Grouping together data and operations

▪ Data hiding

• In object-oriented programming it is required that the data

members of classes could not be accessed directly from the

outside

• The type struct offers complete access to its members by

default, whereas the class type completely hides its members

from the outside

• The access of class elements can be defined by programmers as

well with the keywords private, protected and public.

▪ Data hiding

▪ Constructors

• A constructor is a member function the name of which

corresponds to the name of the class and has no return type.

• A constructor only has to initialise the memory space already

allocated for the object

• A class has two constructors by default: a constructor without

parameters (default) and a copy constructor

▪ Constructors

▪ Constructors

▪ Constructors

• Constructors with and without parameters are often contracted

by introducing default arguments:

▪ Constructors

• Using member initialisation lists

▪ Constructors

• Explicit initialisation of objects

▪ Destructor

• C++ offers a special member function, the destructor, in which

we can free the allocated resources

• The name of a destructor has to be provided as a class name

with the tidle character (~)

• A destructor, just like constructors, does not return any value

▪ Destructor

▪ Destructor

• If a destructor is not written for a class, the compiler

automatically adds an empty destructor for that class

▪ Objects of a class, the pointer this

The class Employee and its objects

▪ Objects of a class, the pointer this

• Each member function has an invisible parameter (this) in which

a pointer to the actual object is passed to the function when it is called

• All references to data members are inserted in a program code

automatically in the following way:

▪ Objects of a class, the pointer this

• Programmers may also use the pointer this within member

functions

❖ More about classes

❖ Operator overloading

▪ Static class members

• A static data member that is created in only one instance belongs

directly to the class; therefore it is available for it even if there

are no objects for that class

• A static data member should not be initialised within its class

(independently of its access restriction)

• If a static data member is public, then it can be used anywhere in

the program code by the name of the class and the scope

operator (::)

▪ Static class members

▪ Static class members

▪ How to structure classes

• Implicit inline member functions

▪ How to structure classes

• Class structures in C++/CLI applications

▪ How to structure classes

• Storing member functions in separate modules

▪ Friend functions and classes

• The friend mechanism makes it possible for us to access the

private and protected members of a class from a function

outside the class

▪ Friend functions and classes

▪ What can we also add to classes?

• Constant data members of objects

▪ What can we also add to classes?

• Reference type data members

▪ What can we also add to classes?

• Data members as objects

▪ What can we also add to classes?

• Pointers to class members

type int,

void

(Class::*pf unct )(int);

pfunct may point to a member function

that is called with an argument of

type int and that returns no value.

In order to define pointers correctly, we have to use the name of the class and the scope operator:

▪ What can we also add to classes?

• Pointers to class members

▪ What can we also add to classes?

• Pointers to class members

By using typedef, expressions containing pointers are easier to

be handled:

❖ More about classes

❖ Operator overloading

• An operator function can be used if one of its parameters is a

class of type class or struct General declaration of operator

functions:

Where the sequence op can be replaced by any of the following

operators:

• The following operators cannot be overloaded : member

selection (.), indirect member selection (.*), scope (::),

conditional (?:) and the operators sizeof and typeid since their

overloading would result in undesired side effects

• The assignment (=), the "address of" (&) and the comma (,)

operations can be applied to objects without overloading.

• Overloading operators does not result in modifying the operator

precedence and associativity, and it is not possible to introduce

new operations

▪ Creating operator functions

Expression Operator( ♣ ) Member function External function

▪ Creating operator functions

• The operators =, (), [] and -> can only be overloaded by

non-static member functions

• The operators new and delete are overloaded with static

member functions

• All other operator functions can be created as member functions

or external (in general friend) functions.

▪ Creating operator functions

• Binary operands:

▪ Creating operator functions

• Unary operands:

▪ Creating operator functions

▪ Creating operator functions

▪ Creating operator functions

▪ Using type conversion operator functions

▪ Using type conversion operator functions

▪ Extending classes with input/output operations

• To "teach" I/O data streams based on classes to handle the

objects of user-defined classes

▪ Extending classes with input/output operations

▪ Extending classes with input/output operations

❖ Classes and objects

❖ Inheritance (derivation)

❖ Polymorphism

❖ Class templates

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• Derivation means that a new class inherits the public and

protected properties (data members) and behaviour (member

functions) of already existing classes and it then uses them as its own

➢ already existing classes may be extended with a new class,

➢ new data members and member functions may be defined

➢ or inherited member functions may be reinterpreted (replaced) if they become deprecated concerning their functioning

(polymorphism).

• class A, that is derived or from which

members are inherited: base class , ancestor

class , parent class, superclass

• the operation: inheritance , derivation ,

extending, subclassing

• class B, the result of derivation: descendant

class, derived class, extended class, child

class, subclass

above:

class ClassA {//

};

class ClassB : public ClassA {//

};

The multiple inheritance of I/O classes in C++

Hierarchy of geometrical classes

❖ Initialising base class(es)

❖ Accessing class members in case of inheritance

❖ Virtual base classes in case of multiple inheritance

❖ Inheritance and/or composition?

• A derived (descendant) class is a class that inherits its data

members and member functions from one or more already

defined class(es).

• The class from which a derived class inherits is called base class

(ancestor class)

• A derived class inherits all the members of its base class;

however, it only have access to the public and protected

members of its base class as its own

• The place where a derivation is indicated in a program code is

the class header where the mode of derivation (public,

protected, private) is indicated before the names of base classes:

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79

• The keywords public, protected and private used in a derivation

list restrict the access of inherited (public and protected)

members in their new classes:

Mode of inheritance Access in the base class Access in the derived class

protected

public protected

protected

protected protected

protected

private

private

• The access of any member (the access type of which is protected

or public in the base class) can be manually set directly.

❖ Initialising base class(es)

❖ Accessing class members in case of inheritance

❖ Virtual base classes in case of multiple inheritance

❖ Inheritance and/or composition?

• In order that base class(es) be initialised, it is the extended

version of member initialisation lists that is used.

❖ Initialising base class(es)

❖ Accessing class members in case of inheritance

❖ Virtual base classes in case of multiple inheritance

❖ Inheritance and/or composition?

▪ Accessing inherited members

▪ Accessing inherited members

The members of the base

Point2D()::PrintOut(), GetPoint3D(), Move(int…), Move(const…), PrintOut()

▪ The friend relationship in inheritance

• In a derived class, a friend of the base class can only access the

members inherited from the base class

• A "friend" of a derived class can only access public and

protected members from the base class

❖ Initialising base class(es)

❖ Accessing class members in case of inheritance

❖ Virtual base classes in case of multiple inheritance

❖ Inheritance and/or composition?

• In case of multiple inheritance, it may be a problem if the same

base class appears as many instances in the derived class

• If virtual base classes are used, problems of that type can be

avoided

Using virtual base classes

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❖ Initialising base class(es)

❖ Accessing class members in case of inheritance

❖ Virtual base classes in case of multiple inheritance

❖ Inheritance and/or composition?

• A big advantage of C++ programming language is that it supports

the reusability of program code

modifying the original one

• If the object-oriented tools of C++ are used, there are three

approaches to choose from:

➢ The most simple and frequent reuse of a code stored in a given

class is when an object instance is created or when already

existing objects (cin , cout , string , STL etc.) are used in a

program

➢ Another possibility is to place objects of other classes in our own

codes as member objects ➔ This method is called composition

If the new object will only contain a pointer or a reference to

other objects, it is called an aggregation.

➢ The third solution: when a new class is created by public

derivation from other classes, then the relationship is of an

is-a type ➔ is-a derived object behis-aves exis-actly the sis-ame wis-ay is-as its

ancestor class

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▪ Reuse with composition

▪ Reuse by public inheritance

❖ Classes and objects

❖ Inheritance (derivation)

❖ Polymorphism

❖ Class templates

101

• Coercion polymorphism means implicit and explicit type casts

➢ In that case, the polymorphism of a given operation is made

possible by different types that may be converted if needed

• As an opposite to coercion, the so-called ad-hoc (“for that

purpose”) polymorphism is better known by the name of

function overloading

➢ In that case, a compiler chooses the appropriate function from

the variants on the basis of parameter types

the same code with any type

➢ In C++, parametric polymorphism is realised by function and

class templates Using templates actually means reusing a C++

source code

❖ Redefining virtual functions

❖ Early and late binding

❖ Virtual destructors

❖ Abstract classes and interfaces

❖ Run-time type informations in case of classes

• A virtual function is a public or protected member function of

the base class

• It can be redefined in the derived class in order that the behavior

of the class would change

• A virtual function is generally called by a reference or a pointer

of a public base class, the actual value of which is determined at run-time (dynamic binding, late binding)

• Declaration of the virtual function:

❖ Redefining virtual functions

❖ Early and late binding

❖ Virtual destructors

❖ Abstract classes and interfaces

❖ Run-time type informations in case of classes

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• Virtual functions and public inheritance make it possible to create external functions that can be called by every object in the class hierarchy:

❖ Redefining virtual functions

❖ Early and late binding

❖ Virtual destructors

❖ Abstract classes and interfaces

❖ Run-time type informations in case of classes

▪ Static early binding

• During early binding, compilers integrate statically direct

member function calls into the code

Early binding example