Object Oriented Programming has a special feature called data abstraction. Data abstraction allows ignoring the details of how a data type is represented. While defining a class, both member data and member functions are described. However while using an object (that is an instance of a class) the built in data types and the members in the class are ignored. This is known as data abstraction. This can be seen from the above example.
Example
An example to show how public member data and public member functions are accessed outside the class.
#include <iostream.h>
#include<conio.h>
class base
{
public: int sl,s2;
public:
void inp_val()
{
cout<<“input the values of sl and s2 “;
cin>>sl>>s2;
}
void disp()
{
cout<<sl <<” “<<s2;
cout<<“\n” ;
}
};
void main()
{
clrscr();
base o1;
o1.inp_val();
o1.disp();
}
The first occurrence of the keyword public (or private) before a member data or a member function makes the compiler assume the types of accesses of all the members following this to be of the first occurrence type. However, if the types of accesses of member data and member functions are different, then the access type should be explicitly mentioned in each case.
Example
An example to show that private member data cannot be accessed outside the class if the member functions which involve this data are also private.
#include <iostream.h>
#include<conio.h>
class base
{
private: int sl,s2;
void inp_val()
{
cout<<“input the values of s1 and s2 “;
cin>>sl>>s2;
}
void disp()
{
cout<<sl <<” “<<s2;
cout<<“\n” ;
}
};
void main()
{
clrscr();
base o1;
o1.inp_val();
o1.disp();
}
On the execution of the above program, following error messages will appear.
error messages
Error oop22.cpp 26 : ‘base::inp-val()’ is not accessible
error oop22.cpp 27: ‘base::disp() ‘ is not accessible
Example
Modified version of Example in which member data are private but the member function which invoke the private data members are public. This will not cause any error as in example
#include <iostream.h>
#include<conio.h>
class base
{
private: int sl,s2;
public: void inp_val()
{
cout<<“input the values of sl and s2 “;
cin>>sl>>s2;
}
void disp()
{
cout<<sl <<” “<<s2<<“\n “;
}
};
void main()
{
clrscr();
base o1;
o1.inp_val();
o1.disp();
}
Dinesh Thakur holds an B.C.A, MCDBA, MCSD certifications. Dinesh authors the hugely popular