object oriented programming in c++ · compiling multiple .cpp les wenqiang chen object oriented...

StructureClasses & Objects

InheritancePolymorphism

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Object Oriented Programming in c++

Wenqiang Chen

Department of Computing and SoftwareMcMaster University

Tutorial 11

Wenqiang Chen Object Oriented Programming in c++



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Outline I

1 Structure

2 Classes & ObjectsMember FunctionsAccess ModifierConstructorDestructorEncapsulationOverloading

Function OverloadingOperator Overloading

3 InheritanceInheritanceRedefining functionsconstructor and destructor in derived class




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Outline II

4 PolymorphismPolymorphismVirtual FunctionVirtual DestructorExample

5 Additional contentsHeader filesCompiling multiple .cpp files




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Structure

Definition: A group of data elements grouped together under onename.

struct type_name {member_type1 member_name1;member_type2 member_name2;member_type3 member_name3;..

};

or

struct type_name {member_type1 member_name1;member_type2 member_name2;member_type3 member_name3;..

} object_names;




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Structure example

#include <iostream>#include <string>using namespace std;

struct contact_info {string name;int age;string address;

} person1, person2;

void printContact(contact_info contact);

int main() {person1.name = "Michael";person1.age = 22;person1.address = "23 Emerson st. Hamilton";person2.name = "Sam";person2.age = 21;person2.address = "23 Emerson st. Hamilton";

printContact(person1);cout << endl;printContact(person2);return 0;

}void printContact(contact_info contact) {

cout << "Name: " << contact.name << endl;cout << "Age: " << contact.age << endl;cout << "Address: " << contact.address << endl;

}




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Member FunctionsAccess ModifierConstructorDestructorEncapsulationOverloading

What are classes?

Specify the form(blueprints) of an object

Combines data representation and methods for manipulatingthat data into one neat package

data and functions within a class are called members of theclass.




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Defining and using classes

class Box{public:

double length;double width;

};int main(){

Box box1;Box box2;box1.length = 2;box1.width = 3;

}




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Definition: Functions that are members of a class(belongs to theclass).

Can be defined within the class definition or outside of classusing scope resolution operation(”::”)

Has access to all members of the class




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Member function definition

#include <string>#include <iostream>using namespace std;class Box {

public:double length;double width;void printShape();

};int main() {

Box box1;box1.printShape();

}void Box::printShape() {

cout << "square";}




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Access Modifier and scope

Access public protected private

Same class yes yes yesDerived classes yes yes noOutside classes yes no no




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Modifier example

class Box{

\\public variables and member functionspublic:

double length;void setWidth( double wid );double getWidth( void );

\\private variablesprivate:

double width;\\protected variablesprotected:

double height;};




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Constructor

A class constructor is a special member function of a class that isexecuted whenever we create new objects of that class.

Must have exact same name as the class.

Must not have any return type.

Useful for setting initial values for certain member variables.

Allows overloading.

Constructor can call other Constructor (Constructordelegation).

Cannot use Constructor like other member function. e.g.ClassName.Constructor()




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Constructor example

#include <string>#include <iostream>using namespace std;class Box {public:

Box(); //ConstructorBox(double len, double wid);double length;double width;

};int main() {

Box box1;Box box2(23,42);

}Box::Box() {

cout << "box is created." << endl;}Box::Box(double len, double wid) : length(len), width(wid) {

cout << "box of " << length << " and " << width << " is created." << endl;}




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A destructor is a special member function of a class that isexecuted whenever an object of it’s class goes out of scope orwhenever object is ”deleted”.

Must have exact same name as the class prefixed with a tilde( )

Cannot return a value or take any parameters.

Contains code to delete all dynamic variables created by theobject.

A class can only have 1 Destructor.




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Destructor example

#include <string>#include <iostream>using namespace std;class Box {

public:Box(); //Constructor~Box(); //Destructorstring *str = new string;double length;double width;

};int main() {

Box box1;}Box::Box() {

cout << "box is created." << endl;}Box::~Box(){

delete str;cout << "string is deleted" <<endl;cout << "box is deleted" << endl;

}




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Encapsulation

Bundling data and functions and exposing only the interfaces(hiding the implementation details) to the user.

Using access modifiers : private, protected and public

Ok to make everything private.




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Function Overloading

Have multiple definitions for the same function name in thesame scope

Definition of the function must differ from each other by thetypes and/or the number of arguments in the argument list

Cannot overload function declarations that differ only byreturn type. e.g. void print() vs int print();




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Function overloading example


Box();void enlarge();void enlarge(double l, double w);double length;double width;

};

int main() {Box box1;box1.enlarge();box1.enlarge(20,20);

}Box::Box() {

length = 2;width = 2;

}void Box::enlarge() {

length++;width++;cout << "new size: " << length << " " << width << endl;

}void Box::enlarge(double l, double w) {

length+=l;width+=w;cout << "new size: " << length << " " << width << endl;

}




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Operator Overloading

Redefine or overload most of the built-in operators

Allows you to use operators with custom types.

defined using keyword ”operator” followed by the symbol forthe operator being defined

Overloaded operator has a return type and a parameter list.




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Operator overloading example


Box ();Box operator+(const Box& box2){

Box box;box.length = this->length + box2.length;box.width = this->width + box2.width;return box;

}double length;double width;

};int main() {

Box box1;Box box2;Box box3 = box1 + box2;cout<< box3.length <<" " << box3.width <<endl;

}Box::Box() {

length=2;width=2;

}




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InheritanceRedefining functionsconstructor and destructor in derived class

Inheritance

Inheritance is the process by which a new class(derived class) iscreated from another class(base class)

Derived class automatically has all the member variables andfunctions of the base class

Derived class can have additional member variables and/ormember functions

The derived class is a child of the base or parent class

Can derive multiple base class




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Defining inheritance

class Box {public:

double length;double width;

};class Crate: public Box {public:

double height;};class ColorCrate: public Crate{public:

string color;};




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Derived class has the option to redefine member functionsinherited from base class

Only redefine functions as needed .

Derived class can have additional member variables and/ormember functions.

The derived class is a child of the base or parent class.

Can derive multiple base class.

Destructor, Copy Constructor, assignment operators are notinherited.

Base class member function can still be called by usingDerivedClass.BaseClass::function




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Redefining functions example

class Box {public:

Box();void enlarge();void enlarge(double l, double w);double length;double width;

};class Crate: public Box {public:

void enlarge();};




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constructor and destructor in derived class

Default constructor of base class is automatically called whenderived class is created (unless explicitly call other constructor).

Constructor are called in a Top to Bottom order (Parent to Child).

Destructor are called in a Bottom to Top order (Child to Parent).




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Derived Constructor example

#include <iostream>using namespace std;class Box {public:

Box();double length;double width;

};

class Crate: public Box {public:

Crate();double height;

};

class ColorCrate: public Crate {public:

ColorCrate();string color;

};int main() {

ColorCrate c;}Box::Box() :length(0), width(0) {

cout << "box is created" << endl;}

Crate::Crate() :height(0) {

cout << "crate is created" << endl;}

ColorCrate::ColorCrate() {cout << "color crate is created" << endl;

}




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PolymorphismVirtual FunctionVirtual DestructorExample

Polymorphism

Refers to the ability to associate multiple meanings with onefunction name using a mechanism called late binding

Polymorphism is a key component of the philosophy of objectoriented programming

Call to a member function will cause a different function to beexecuted depending on the type of object that invokes thefunction.




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Declared using keyword ”virtual”.

Signals to the compiler that we don’t want static linkage forthis function.

Allows late binding.




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Virtual destructors

Destructors in derived class should be virtual.

why?

Because destructor of the derived class automatically callsdestructor of the base class.

Apply this with polymorphism.

e.g. when you delete base class Box, it calls destructor of derivedclass, which then calls destructor of base class




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Polymorphism example

#include <iostream>using namespace std;class Box {public:

Box();virtual void print()=0;double length;double width;virtual ~Box();

};

class Crate: public Box {public:

Crate();virtual void print();double height;virtual ~Crate();

};

class ColorCrate: public Crate {public:

ColorCrate();virtual void print();string color;virtual ~ColorCrate();

};int main() {

Box *b = new ColorCrate;

b->print();delete b;

}

Box::Box() :length(0), width(0) {

cout << "box is created" << endl;}




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Polymorphism example cont.

Box::~Box() {cout << "box is created" << endl;

}Crate::Crate() :height(0) {

cout << "crate is created" << endl;}Crate::~Crate() {

cout << "crate is deleted" << endl;}void Crate::print() {

cout << "This is a crate" << endl;}

ColorCrate::ColorCrate() {cout << "color crate is created" << endl;

}

ColorCrate::~ColorCrate() {cout << "color crate is deleted" << endl;

}

void ColorCrate::print() {cout << "This is a colorful crate" << endl;

}




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Header filesCompiling multiple .cpp files

Header

Separate class declaration and actual definition of class.Box.h

#ifndef BOX_H_#define BOX_H_

class Box {public:Box();void print();double length;double width;~Box();

};#endif /* BOX_H_ */

Box.cpp#include <iostream>#include "Box.h"using namespace std;Box::Box():length(0),width(0){

cout<<"Box is created";}void Box::print(){

cout<<"This is a box";}

Box::~Box(){

}int main(){

Box b;}




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Header filesCompiling multiple .cpp files

To compile project with multiple cpp files:run : g++ Class1.cpp Class2.cpp Class3.cpp ....Classn.cpp -ooutput.exe


object oriented programming in c++ · compiling multiple .cpp les wenqiang chen object oriented...

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