4/23/08 CS 331 – OOP Group 1

Object Oriented Programming in C++

Presented by Errol Russell

4/23/08 CS 331 – OOP Group 2

History of C++

• Created by Bjarne Stroustrup in 1979 at Bell Labs

• Desire to add class constructs to the already popular C language.

• “C with Classes” • Provides a number of features that “spruce up”

the C language.• Old C language with Classes/OOP added into

the mix.• Provides the capabilities for object-oriented

programming.

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History of C++

• 1986: Bjarne Stroustrup releases his book The C++ Programming Language

• 1998: Standard ratified as ISO/IEC 14882:1998• 1999: Draft standard ISO/IEC 14882:1999• 2003: Current version is the 2003 version,

ISO/IEC 14882:2003. • 200X: A new version of the standard (C++0x) is

currently being developed. Will probably be ISO/IEC 14882:2009

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The C++ Paradigm

• A programming paradigm is a fundamental style of programming.

• C++ is a multi-paradigm language– Does not strictly adhere to one paradigm over

another– Incorporates multiple paradigms together

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The C++ Paradigm

• Procedural Programming Paradigm – Procedures

• Series of computational steps to be carried out, called at any point during a program's execution.

• Abstraction Paradigm– Control Abstraction– Data Abstraction

• Generic Programming Paradigm– Think templates

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The C++ Paradigm

• Object Oriented Programming (OOP) Paradigm– A notable paradigm in C++ that was not in C,

and the focus of the rest of this talk– "objects" and their interactions to design

applications and computer programs.– Based on several techniques

• Encapsulation• Modularity• Polymorphism• Inheritance

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Specific Enhancements to C

• Templates– Write code without having to consider a specific data

type. Used heavily when creating Abstract Data Types

• Exception Handling– Helps avoid problems that would disrupt the normal

flow of execution. “Catch” problems before they happen.

• Polymorphism– Can assign different meanings/usages to an object

based on context. For example, you could use an integer as a Boolean in some cases.

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Specific Enhancements to C

• Operator Overloading– Operators can be re-written to perform different tasks

• Multiple Inheritance – One class can inherit from multiple classes

• “Diamond Problem” solved with virtual inheritance

• Classes– Constructs for objects

• Virtual Functions– “. . .behavior is determined by the definition of a function with the

same signature furthest in the inheritance lineage of the instantiated object on which it is called.”

– It “knows” which of the functions it needs to execute the code for

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New Syntax in C++

• new – creates a new instance of an object

• delete – destroys an object

• The : operator used for inheritance

• this – self-referential object pointer

• Error handling– try– catch– throw

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Example of Inheritanceclass Shape{

public:int sides;void setSides(int n) {sides=n;};

};class Square : public Shape{

public:void getSides() {cout<<sides;}; // we have access to “sides” because of the

// inheritance from “Shape”. The nice thing about// OOP and inheritance is that we don’t have to // rewrite a bunch of code, we just inherit it.

};

int main(){Square X;X.setSides(4);X.getSides();return 0;

}

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The Output

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Example of Virtual Functionsclass Shape{

public:virtual void message()=0;

};class Square : public Shape{

public:void message() { cout<<"I have 4 sides!"<<endl;}

};class triangle : public Shape{

public:void message() {cout<<"I have 3 sides!"<<endl;}

};int main(){

Shape* shapez[2];shapez[1]=new Square;shapez[2]=new triangle;

for (int i = 1; i < 3; i++) {shapez[i]->message();

} return 0;}

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What it Prints

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The Virtual Function Table

• Dynamically bound methods can be called from any instance of a class or its derived classes

• Methods stored only once in a virtual function table (vtable).

• Function calls are represented as offsets from the beginning of the table.

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Virtual Functions/Tables and Dynamic Binding

• The program contains a base class and two derived classes.

• The base class is abstract and defines a pure virtual function

• Derived classes provide the appropriate implementation

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Virtual Functions/Tables and Dynamic Binding

• A virtual function table is a mechanism used in OOP language implementation in order to support dynamic run-time method binding.

• That is, virtual functions and the virtual function table are used to support dynamic binding.

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Virtual Functions/Tables and Dynamic Binding

• The virtual functions in the previous program give an example of dynamic binding.

• Dynamic binding happens when invoking a derived class's member function using a pointer to its super class.

• The implementation of the derived class will be invoked instead of that of the base class.

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Virtual Functions/Tables and Dynamic Binding

• Languages like C++ separate the interface of objects from the implementation

• They tend to use the virtual function table approach because it

• Allows objects to use a different implementation by using a different set of method pointers.

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Virtual Functions/Tables and Dynamic Binding

• When the program calls the “sides” method on a Shape pointer (which can point to any of the base or derived classes)

• Run-time environment must be able to determine which implementation to call, depending on the actual type of object Shape points to.

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A Diagram of Virtual Function Flow

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Strengths of C++

• “single, portable language that works better than any alternative in each of several areas”

• “works well when [a more desirable language] is. . .not available, and because it interfaces easily with the libraries and the other languages you use”

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Strengths of C++

• Execution speed

• Multi-paradigm

• C++ is like a “glue”– “well suited to tying together the various parts

of a programming project”

4/23/08 CS 331 – OOP Group 23

Weaknesses of C++

• It is a "bloated" and complicated language– The ISO standard of the C++ language is

about 310 pages (excluding library)

• No language features to create multi-threaded software– Can multithread when it interfaces with OS or

3rd party applications, but creates portability concerns

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My References

• http://www.research.att.com/~bs/books.htmlhttp://www.cantrip.org/realworld.html

• Sebesta’s Programming Languages 8th edition.

• Deitel & Deitel’s How to Program C++ 5th Edition

• http://www.java2s.com/Code/Cpp/Class/Asimpleexampleofinheritance.htm