Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 1 - C++ Inheritance Data Abstraction and Abstract Data Types Abstract Data Type Encapsulated data

Copyright 2006 Oxford Consulting, Ltd

1 February 2006

- 1 -

C++ InheritanceC++ Inheritance

Data Abstraction and Abstract Data Types

Abstract Data Type

Encapsulated data type

Accessible only through interface

Properties Defined by the interface not by the Internal structure or

Implementation

Data Abstraction

Effective technique for extending predefined type system

When one has a single clearly defined concept


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Inheritance

In C++

Inheritance is a mechanism for

Building class types from other class types

Defining new class types to be a ….

Specialization

Augmentation

of existing types


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Inheritance

Inheritance is a familiar concept….

Inherit From parents

In Biology

Kingdom

Phylum

Class

Order

Family

Genus

Species

Vehicles

Land BasedAuto Bicycle


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Inheritance

Subgroupings with respect to a parent are called Subclass Derived Class Children

The subclass Inherits Characteristics Properties Capabilities

The subclass can modify or extend inherited abilities


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Inheritance

Vehicle

Class

Land Based

Bicycles Autos

myVehicle

myLandBased

myAuto myBicycle

Instance


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Inheritance

Instance hierarchy follows the class hierarchy

Single InheritanceEach object has a single parent

Class

Instance

Multiple InheritanceClasses inherit from multiple base classes

Defines a relationship

Between several (independent) class types


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Multiple InheritanceVehicleVehicle

Land BasedLand Based

AutomobileAutomobile Motor BoatMotor Boat

AutoBoatAutoBoat

Water BasedWater Based

Multiple Parents Common Ancestor


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Multiple Inheritance

Can also have inheritance without common parent….

Motor Boat Inherits from 2 independent classes Vehicle Taxable Item

Vehicle Vehicle

Water BasedWater Based Luxury ItemLuxury Item

MotorBoatMotorBoat

Taxable ItemTaxable Item


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Virtual InheritanceThe derived class AutoBoat……

Inherits Attributes and Properties

From

Automobile

Motor Boat

Vehicle

VehicleVehicle

Land BasedLand Based

AutomobileAutomobile Motor BoatMotor Boat

AutoBoatAutoBoat

Water BasedWater Based


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Inheritance - Derivation Hierarchy

The class vehicle is an abstraction…..

It represents an encapsulation of commonProperties

Attributes

Its sole purpose

Define a class from which to derive other classes…...It encapsulates common

Data members

Function members

Called

Abstract base class

Abstract super class


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Inheritance - Abstract Super Class

Key element in the derivation hierarchy

Ensures that all derived classes

Share a common set of class members inherited from

abstract super class

Provides a common public interface to the class hierarchy


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C++ Class Derivation

Any class can serve as a base class...Thus a derived class can also be a base class.Worth spending time at the outset of a design to develop

sound definition.

syntax

class DerivedClassName : specification BaseClassNameDerivedClassName - the class being derivedspecification - specifies access to the base class

memberspublicprotectedprivate

- private by default


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class A be derived from base class B or C

B public

C private

1.class A : public B

2.class A : private C


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class A : public B

In class A

The inherited public members of B

Appear as public members of A

If myValue is a public data member of B

myValue can be accessed publicly through instances of A

A d;

d.myValue; // ok


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C++ Class Derivationclass A : private B

In class AThe inherited public members of BAppear as private members of A

if myValue is a public data member of BmyValue cannot be accessed publicly and directly through

instances of A

A d;

d.myValue; // compile error

Function members of A can still access public members of B

as public


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C++ Class Derivation - Public Derivation

class A { }

class C : public B { }

Objects are created from the inside out and ...

A PartA Part A PartA Part

B PartB Part

C PartC Part

C ObjectC Object

B PartB Part

C PartC Part

Constructors

A :: A

B :: B

C :: C


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C++ Class Derivation - Public Derivation

class A { }

class C : public B { }

Objects are destructed from the outside in:

C PartC Part C PartC Part

B PartB Part

A PartA Part

C ObjectC Object

B PartB Part

A PartA Part

Destructors

C :: C

B :: B

A :: A


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C++ Class Derivation - Constructors and Destructors

Constructors and destructors are not inherited….

Initialization and Deinitialization Implemented as series of constructor calls

Base

Derived classes

Different constructors and destructors collaborate to complete the

tasks


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C++ Class Derivation - Constructors and Destructors

When derived object instantiated, memory allocated for

Base object

Added parts

Initialization then occurs in two stages…...

Base class constructors invoked to initialize the base objects

Derived class constructor invoked to complete the task

Derived class constructor

Specifies base class constructor in the initialization listIf no constructor in the base class use the default

If the base class is derived the procedure applied recursively


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C++ Class Derivation - Constructors and DestructorsInherited Member Initialization

If the base class has only a default constructorInitialize the member values in body of the derived class constructor

If the base class has constructor with argumentsThe initialization list is used to pass arguments to the base class constructors

syntax

DerivedClass ( derivedClass args ) : BaseClass ( baseClass args ){

DerivedClass constructor body}


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C++ Class Derivation - Member Access Under Derivation

C1 Defines the base class members

C2 Over rides c ( )Defines e ( )

C3 Over rides d ( )

If C3 accessesa self c2 c1

b self c2 c1

c self c2

d self

e self c2

C1

C1

C2

C2

C3

C3

data member afunction member b()function member c()function member d()

function member c()function member e()

function member d()


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1. Access to inherited members by derived members and friends

Is independent of the base class designation in the derivation specification

Access is allowed to all non-private inherited members

Access is not allowed to private members (of the parent)


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2. Access to inherited members by functions outside the derivation hierarchy is driven by the base class designation in the derivation specification.

If the specification ispublic

public members remain public

protected members remain protected

protected

inherited non-private members accessible as protected

private

no outside access


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3. Over riding - An inherited member that is normally visible can be masked

Define a derived class member with the same name

This is not good practice with non-virtual functions.


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C++ Class DerivationDerivation Guidelines

1. Derivation is not always the best way to extend the system.

2. Use public derivationWhen the derived object is a kind of (AKO) base class

3. Use private derivationWhen the derived object is not a kind of base class but

derivation makes code development easier.

4. Use protected derivationWhen private derivation is suitable but member access

from further derived classes is desirable.


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Base Class Member Specification Guidelines

Classes designed as base classes are the same as ordinary

classes

Declare as protected Function and data members Intended to be inherited but

not

intended to be public.

Declare as virtual Function members intended to be implemented by derived

classes.


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C++ Class Derivation - Member LayoutSingle Inheritance

struct A

{int a1;

void af ( );

};

struct B : A

{int b1;

void bf1 ( );

};

B :: b1

A*, B* ->

A :: a1 A* ->

A :: a1


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C++ Class Derivation - Member Layout

Multiple Inheritance

struct C

{int c1;

void cf ( );

};

struct D : A, C

{int d1;

void df1 ( ); };

C :: c1 C* ->

D :: d1

A*, D* ->

C :: c1 C* ->

A :: a1


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C++ Class Derivation - Member Layout

Virtual Inheritance

struct E : virtual A

{int e1;

void ef ( );

};

E :: vbptr

E :: e1

E* ->

SharedMembers


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C++ Class Derivation - Private Derivation

If the derivation specification is changed to….. class BaseClass{public:

BaseClass() {baseValue = 20;}int baseValue;

};

class DerivedClass : private BaseClassmain (void){

DerivedClass child;child.baseValue = 30; // compile error

}


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C++ Class Derivation - Private Derivation

Exemptions

C++ provides a means through which individual members

can be made exempt from a private derivation

syntax

Data members

BaseClass :: data member

Function members

BaseClass :: function member


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C++ Class Derivation - Protected Derivation

If the derivation specification is changed to

Class DerivedClass : protected Base Class Public and protected members are inherited as protected Protected members

Act as public within the derivation hierarchy Act as private from the outside

Class member declared as protectedActs as

public member to Member functions and friends of derived

classprivate member to

The rest of the program


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C++ Class Derivation - Conversions Under DerivationThere are four predefined conversions between a derived class

and a public base class

1. Derived class object.Implicitly converted into a public base class object.

2. Derived class reference.Implicitly converted into a public base class reference.

3. Derived class pointer.Implicitly converted into a public base class pointer.

4. Pointer to a member of a base class.Implicitly converted to a pointer to that member in a

publicly derived class.


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Apple a, *aPtr = &a; // Derived Class

Fruit f, *fPtr = &f; // Base Class

1. a may be used anyplace f is used - contains a base class

2. a may be used as a reference anywhere a reference to f is used - contains a base class.

3. the pointer aPtr may be used anywhere fPtr is used - contains a base class

4. fp -> seeds can be used anywhere ap -> seeds is used - inherited from fruit.

C++ Class Derivation - Conversions Under Derivation

1

4

stem

seeds

this

1

4

2

3

stem

stem

seeds

skin

this


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C++ Class Derivation - Conversions Under Derivation

Apple a, *aPtr = &a; // Derived Class

Fruit f, *fPtr = &f; // Base Class

1. Fruit *fp = new Apple;

Implicit conversion - 3

2a.Apple *ap = new Fruit;

Error No implicit conversion

Skin uninitialized and undefined

Stem = 1 but *ap -> stem unitialized

2b.Apple *pa = (Apple *) new Fruit;

Legal - Explicit conversion

Explicit cast - Legal but dangereous

seeds

1

4

2

3

stem

stem

skin

fp -> stem

((Apple *) fp) -> stem


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Overloaded Functions with Class Type Arguments

Overloaded Function Call Resolution

Exact MatchA class argument matches only a formal argument of

its own

class

If class B is derived from class A

Overload function f1

f1 (A a);

f1 (B b);

Then declare an instance of B

B b1;

f1 (b1); // is legal and resolvable


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Standard Conversions - Object ConversionA derived class Object, Reference, or Pointer is implicitly

converted into a public base class type.



f1 (A a);

f1 (C c); // C is not in the derivation hierarchy


B b1;

f1 (b1); // is legal and resolvable to the proper

// function


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Standard Conversions - void ConversionA pointer of any class type is implicitly converted into a

pointer of type void.



f1 (C* &c); // C is not in the derivation hierarchy

f1 (void* ); If class B is derived from class A


B b1;

f1 (&b1); // is legal and resolvable to the proper // function


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Standard Conversions - Programmer Defined Conversion

to:

syntax

operator typeName() { body }

typeName - type to convert to from the class

from:

Use the constructor with a single argument

syntax

X::X ( typeName arg ) { body }

typeName - type to convert from to the class


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Copy Constructors and DerivationIf a copy constructor is not supplied for derived class a default copy

constructor is generated

Derived default copy constructor copies Base and member objects

By calling their copy constructors Data members as a memcopy

If a copy constructor is supplied must specify the desired copy

constructors for Base and member objects

syntax

DerivedClass X (const DerivedClass X& object) : BaseClass (object)

object - the object being copied


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Over Riding Inherited Members

When a function name is reused or inherited from multiple base

classes - ambiguity results.

Compiler tries to resolve any such conflicts….

Single PathUse the function in the most immediate scope for

which the

signatures are identical

Multiple PathsUse the scope operator or virtual functions


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Multiple Base Classes

A derived class can inherit from multiple base classes….

syntaxclass DerivedClassName : spec0 base class0, spec1 base class1, ... specn base classn,

DerivedClassName - the class being derived

Specification - specifies access to the base class

members

public

protected

private


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Multiple Base Classes

Let: class A be derived from base classes B, C, and D

B public

C, D private

1. class A : public B, private C, D

2. class A : private C, public B, private D

3. class A : C, D, public B


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Multiple Base Classes - Inherited Member Initialization If the base class has only a default constructor

Initialize the member values in the body of the derived class

constructor A constructor with arguments

The init list used to pass args to the base class constructors Invocation is left to right, depth first

syntaxDerivedClass ( dCl args ) : BC0 (bC0 args), BC1 (bC1 args), ...BCn

( bCn args),{

DerivedClass constructor body

}

Documents

Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 1 - C++ Inheritance Data Abstraction and Abstract Data Types Abstract Data Type Encapsulated data