Computer Notes - Private Inheritance

8/3/2019 Computer Notes - Private Inheritance

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Private Inheritance

http://ecomputernotes.com


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Class Collectionclass Collection {

...public:

void AddElement(int);bool SearchElement(int);

bool SearchElementAgain(int);bool DeleteElement(int);

};http://ecomputernotes.com


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Class Setclass Set: private Collection {

private:...

public:void AddMember(int);

bool IsMember(int);bool DeleteMember(int);



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Specialization (Restriction) the derived class is behaviourally

incompatible with the base class

Behaviourally incompatible meansthat base class cant always be

replaced by the derived class



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Specialization (Restriction) Specialization (Restriction) can be

implemented using private andprotected inheritance



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Example Specialization

(Restriction)Person

age : [0..125]

Adult

age : [18..125]

setAge( a )

setAge( a )

age = a

If age < 18 then

errorelse

age = a


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Exampleclass Person{

protected:int age;

public:

bool SetAge(int _age){if (_age >=0 && _age


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Exampleclass Adult : private Person {

public:bool SetAge(int _age){

if (_age >=18 && _age


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Private Inheritance Only member functions and friend

functions of a derived class canconvert pointer or reference of

derived object to that of parent object



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Exampleclass Parent{};

class Child : private Parent{};

int main(){

Child cobj;

Parent *pptr = & cobj; //Error

return 0;

}



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Examplevoid DoSomething(const Parent &);

Child::Child(){

Parent & pPtr =static_cast(*this);

DoSomething(pPtr);

// DoSomething(*this);

}http://ecomputernotes.com


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Private Inheritance The child class object has an

anonymous object of parent classobject

The default constructor and copyconstructor of parent class are called

when needed



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Exampleclass Parent{public:

Parent(){cout


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Exampleclass Child: private Parent{public:

Child(){cout


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Exampleint main() {

Child cobj1;Child cobj2 = cobj1;

//Child cobj2(cobj1);return 0;

}



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Example Output:

Parent Constructor

Child ConstructorParent Copy Constructor

Child Copy Constructor



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Private Inheritance The base class that is more then one

level down the hierarchy cannotaccess the member function of

parent class, if we are using private

inheritance



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Class Hierarchyclass GrandParent{public :

void DoSomething();};

class Parent: private GrandParent{void SomeFunction(){

DoSomething();

}

};



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Exampleclass Child: private Parent

{public:

Child() {DoSomething(); //Error

}



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Private Inheritance The base class that is more then one

level down the hierarchy cannotconvert the pointer or reference to

child object to that of parent, if we

are using private inheritance



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Class Hierarchyvoid DoSomething(GrandParent&);

class GrandParent{};

class Parent: private GrandParent{public:

Parent() {DoSomething(*this);}



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Exampleclass Child: private Parent {

public:Child()

{DoSomething(*this); //Error

}



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Protected Inheritance Use protected inheritance if you want

to build class hierarchy usingimplemented in terms of



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Protected Inheritance If B is a protected base and D is

derived class then public andprotected members of B can be used

by member functions and friends of

classes derived from D



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Class Hierarchyclass GrandParent{public :

void DoSomething();};

class Parent: protected GrandParent{void SomeFunction(){

DoSomething();

}

};



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Exampleclass Child: protected Parent

{public:

Child()

{

DoSomething();

}

}; http://ecomputernotes.com


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Protected Inheritance If B is a protected base and D is

derived class then only friends andmembers of D and friends and

members of class derived from D

can convert D* to B* or D& to B&



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Class Hierarchyvoid DoSomething(GrandParent&);

class GrandParent{

};

class Parent: protected GrandParent{};



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Exampleclass Child: protected Parent {

public:Child()

{DoSomething(*this);

}

};

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Computer Notes - Private Inheritance