Pointer and Object in C++

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POINTER AND
OBJECT IN C++

Pointer to object

How to store address of object into pointer
and access members?
 Ans
 Pointer to object
 Two Ways to
access member
 (*ptr).member
 Ptr->member

Pointer to object

How to store address of object created using new into pointer
and access members?
 new Base(10)
allocate memory
at memory heap
that is to be
pointed by p1

How to create pointer to array of object?

How to call constructor of array of object
through new?

What is this pointer?
 C++ use unique key word called this to represent
object that invokes member function.
 i.e. Compiler store address of invoking object in this!!!!
 Example: obj1.max(obj2)
 Address of obj1 will get stored into this pointer.
 Use of this pointer
 To access data member of invoking object within class
 To return invoking object!!!

To access data member of invoking
object within class
30

To return invoking object!!
30

Pointer to derived class

Note: Base class pointer could point to DerivedNote: Base class pointer could point to Derived
Class object but derived class pointer can notClass object but derived class pointer can not
Point to base class pointer!!!Point to base class pointer!!!
Note: Base class pointer could point to DerivedNote: Base class pointer could point to Derived
Class object but derived class pointer can notClass object but derived class pointer can not
Point to base class pointer!!!Point to base class pointer!!!

Compiler generates error Because derived classCompiler generates error Because derived class
public members can not be Accessed throughpublic members can not be Accessed through
base class Pointer!!!base class Pointer!!!
Reason: Base class pointer can only points toReason: Base class pointer can only points to
Base class object within derived class.Base class object within derived class.

Method Overriding
 Method Overgrind: If same signature of a functionMethod Overgrind: If same signature of a function
in base class as well derived class.in base class as well derived class.
 Binding of Fun. Depend on type of Invoking objectBinding of Fun. Depend on type of Invoking object
 Base class-> base class member functionBase class-> base class member function
 Derived class-> Derived class member funDerived class-> Derived class member fun
 Compile time polymorphismCompile time polymorphism
 Method Overgrind: If same signature of a functionMethod Overgrind: If same signature of a function
in base class as well derived class.in base class as well derived class.
 Binding of Fun. Depend on type of Invoking object.Binding of Fun. Depend on type of Invoking object.
 Base class-> base class member functionBase class-> base class member function
 Derived class-> Derived class member funDerived class-> Derived class member fun
 Compile time polymorphismCompile time polymorphism

Method Overriding
 p->print() call base type print function as type ofp->print() call base type print function as type of
p is Base.p is Base.
 p->print() call base type print function as type ofp->print() call base type print function as type of
p is Base.p is Base.

How to call derived class method using
base class pointer??
 Solution
 Run time polymorphism
 What it mean?
 Binding will done at run time Instead of compile time.
 What happen in Runtime binding
 Based on content of the object compiler will bind the
function definition with specific functional call!!!
 How to instruct to the compiler to do binding at
runtime instead of compile time
 By making base class function virtual. Generally referred as
virtual Function!!!!

Method Overriding
 When compiler find virtual keyword in baseWhen compiler find virtual keyword in base
class member function, Compiler perform runtimeclass member function, Compiler perform runtime
binding instead of compile time binding.binding instead of compile time binding.
Content of p is address of derived class so it callsContent of p is address of derived class so it calls
print() method of derived class!!!!print() method of derived class!!!!
 When compiler find virtual keyword in baseWhen compiler find virtual keyword in base
class member function, Compiler perform runtimeclass member function, Compiler perform runtime
binding instead of compile time binding.binding instead of compile time binding.
Content of p is address of derived class so it callsontent of p is address of derived class so it calls
rint() method of derived class!!!!rint() method of derived class!!!!

Definition: Virtual Function
 A virtual function is a member function which is
declared within base class and is re-
defined (Overridden) by derived class. When you refer
to a derived class object using a pointer or a reference
to the base class, you can call a virtual function for
that object and execute the derived class's version of
the function.

Pointer and Object in C++

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