Class:-

  • Class is a collection of a characteristics and a behaviors.
  • Characteristics means data members defined in the class and behaviors means a member functions/methods which are defined in the class and this methods are applied on to the characteristics of the class.

e.g.

class demo

{

public:

int i,j;

void fun()

{

cout<<”Inside the fun of demo”;

cout<<i;

cout<<j;

}

};

  • In the above example, demo is our class which contains two characteristics as I and j. and both are integers.
  • Behaviors of the demo class is a function fun() which applied on the data types i and j.
  • To use above class we have to create an instance of that class means we have to create an object of that class.

 

e.g.

demo d;

or

class demo d;

  • In the above syntax, we create an object of the class demo named as d.
  • In the C++, writing a keyword class, struct and union while creating an object is optional but in C it is Compulsory.

Struct demo

{

int i,j;

};

Struct demo d; // This is the syntax which is used in C.

Demo d; // This is the syntax which is used in C++.

 

Introduction to C

 

Memory allocation for the class:-

Class demo

{

public:

int i,j,k;

float f;

int fun()

{

cout<<”Inside the fun of demo”;

}

int gun()

{

cout<<”Inside the gun of demo”;

}

};

int main()

{

cout<<sizeof(demo); // 16

demo d;

cout<<sizeof(d); // 16

return 0;

}

  • In this example, memory allocated for our class is 16 bytes, because, this class contains 3 integers and 1 float data type.
  • This class also contains two functions namely as fun() and gun().
  • When we create an  multiple objects of same class then memory allocated for each and every object is 16 bytes.
  • But there is no memory allocation for functions of a class, because, function definitions do not vary across the object but the data members of an objects vary across the object.
  • Important things about the memory allocation of an object is that,

1)    Memory allocation for data types of an object is in sequential manner that is in our example, first 4 bytes contains i, next 4 bytes contains j and so on.

2)    Memory allocated for an object is only for non static data members of an object.

  • We can call member function of the class by using “.” like,

d.fun();

  • But if we have a pointer of that class then we can call the member function using arrow operator like,

e.g.

demo *p = new demo();

p->fun();

  • In this case, p is a pointer which is of the type of a class demo.
  • We allocate a memory dynamically for object of the class demo and base address of that dynamically allocated memory is accepted inside a pointer p and from that pointer p, we can access the member functions as well as data members.

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Written by Sourabh Bhunje

Sourabh Bhunje, B.E. IT from Pune University. Currently Working at Techliebe. Professional Skills: Programming - Software & Mobile, Web & Graphic Design, Localization, Content Writing, Sub-Titling etc. http://techliebe.com/about-us

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