static members in object oriented program.pptx

Static Data Member
• A type of data member that is shared among all objects of class is
known as static data member.
• The static data member is defined in the class with static keyword.
• When a data member is defined as static, only one variable is created
in the memory even if there are many objects of that class.
• A static data item is useful when all objects of the same class must
share a common item of information.
• The characteristics of a static data member are same as normal static
variable.

Static Data Member
• It is visible only in the class, in which it is defined but its lifetime
• Starts when the program starts its execution.
• Ends when the entire program is terminated.
• It is normally used to share some data among all objects of a particular
class.
• The main difference between normal data member and static data
member is that
• each object has its own variable of normal data member.
• On the other hand, static data member is shared among all objects of the class.
• Only one memory location is created for static data member that is shared
among all objects.

Difference Between Normal & Static Data
Members
Object with three normal data
members
Object with two normal data members
and one static data member
200
n
1
a
10
b
Object b1
2
a
20
b
Object b2
1
a
10
b
100
n
Object b1
2
a
20
b
200
n
Object b2

Uses of Static Class Data
• Why would you want to use static member data?
• As an example, suppose an object needed to know how many other
objects of its class were in the program.
• for example :
• In a road-racing game, a race car might want to know how many other cars
are still in the race.
• In this case a static variable count could be included as a member of
the class. All the objects would have access to this variable.
• It would be the same variable for all of them; they would all see the
same count.

Separate Declaration and Definition
• Static member data requires an unusual format.
• Ordinary variables are usually declared and defined in the same
statement.
• Static member data, on the other hand, requires two separate
statements.
• The variable’s declaration appears in the class definition, but the
• Variable is defined outside the class, in much the same way as a global
variable.
• Why is this two-part approach used?
• If static member data were defined inside the class, it would violate the idea
that a class definition is only a blueprint and does not set aside any memory.

Separate Declaration and Definition
• Putting the definition of static member data outside the class also
serves to emphasize that
• the memory space for such data is allocated only once, before the program
starts to execute, and that
• one static member variable is accessed by an entire class; each object does
not have its own version of the variable, as it would with ordinary member
data.
• In this way a static member variable is more like a global variable.

Write a program that counts the number of
objects created of a particular class (1/2)
class yahoo
{
private:
static int n;
public:
yahoo()
{ n++; }
void show()
{
cout<<“you have created ”<<n<<“ objects so far ”<<endl;
}
};

Write a program that counts the number of
objects created of a particular class (2/2)
int yahoo::n=0;
void main()
{
yahoo x,y;
x.show();
yahoo z;
x.show();
}
OUTPUT:
• You have created 2 objects so far.
• You have created 3 objects so far.

How it Works
• The program declares a static data member n to count the number of objects
that have been created.
• The statement int yahoo::n=0;defines the variable and initializes it to 0.
• The variable is defined outside the class because it will be not part of any object.
• It is created only once in the memory and is shared among all objects of the class.
• The variable definition outside the class must be preceded with class name and
scope resolution operator ::.
• The compiler does not display any error if the static data member is not defined.
• The linker will generate an error when the program is executed.
• The above program creates three objects x, y and z. each time an object is
created, the constructor is executed that increases the value of n by 1.

Write a program that creates three objects of class
student. Each of them must assigned a unique roll
number. (Hint: use static data member for unique roll number) (1/2)
class Student
{
private:
static int r;
int rno,marks;
char name[30];
public:
Student()
{ r++;
Rno =r; }
void in()
{
cout<<“enter name:”;
gets(name);
cout<<“enter marks:”;
cin>>marks;
}
void show()
{
cout<<“Roll No:”<<rno<<endl;
cout<<“Name:”<<name<<endl;
cout<<“Marks:”<<marks<<endl;
}
};

Write a program that creates three objects of class
student. Each of them must assigned a unique roll
number. (Hint: use static data member for unique roll number) (2/2)
int Student::r=0;
void main()
{
Student s1,s2,s3;
s1.in();
s2.in();
s3.in();
s1.show();
s2.show();
s3.show();
}

How it Works
• The above program uses a static data member r to assign unique roll
numbers to each object of the class Student.
• The static data member is initialized to 0.
• The constructor increments its value by 1 when an object is created
and then assigns the updated value of r to the data member rno.
• It ensures that each object gets a unique roll number.

Static member function:
• A member function that is declared static has the following properties:
 A static function can have access to only other static members(function or variable)
declared in the same class.
 A static member function can be called using the class name.
like, class_name :: Function_name();
test :: getdata();

• Static Member Function in C++
• Static Member Function in a class is the function that is declared as static because
of which function attains certain properties as defined below:
• A static member function is independent of any object of the class.
• A static member function can be called even if no objects of the class exist.
• A static member function can also be accessed using the class name through the
scope resolution operator.
• A static member function can access static data members and static member
functions inside or outside of the class.
• Static member functions have a scope inside the class and cannot access the
current object pointer.
• You can also use a static member function to determine how many objects of the
class have been created.

• Static members are frequently used to store information that is
shared by all objects in a class.
• For instance, you may keep track of the quantity of newly generated
objects of a specific class type using a static data member as a
counter. This static data member can be increased each time an
object is generated to keep track of the overall number of objects.

• // C++ Program to show the working of
• // static member functions
• #include <iostream>
• using namespace std;
• class Box
• {
• private:
• static int length;
• static int breadth;
• static int height;
•
• public:
•
• static void print()
• {
• cout << "The value of the length is: " << length << endl;
• cout << "The value of the breadth is: " << breadth << endl;
• cout << "The value of the height is: " << height << endl;
• }
• };

• // initialize the static data members
• int Box :: length = 10;
• int Box :: breadth = 20;
• int Box :: height = 30;
• // Driver Code
• int main()
• {
•
• Box b;
•
• cout << "Static member function is called through Object name: n" << endl;
• b.print();
•
• cout << "nStatic member function is called through Class name: n" << endl;
• Box::print();
•
• return 0;
• }

static members in object oriented program.pptx

Recommended

More Related Content

What's hot (20)

Similar to static members in object oriented program.pptx (20)

More from urvashipundir04 (20)

Recently uploaded (20)

static members in object oriented program.pptx