static members in object oriented program.pptx

static members in object oriented program.pptx

• 1.
  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.
• 2.
  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.
• 3.
  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
• 4.
  Uses of StaticClass 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.
• 5.
  Separate Declaration andDefinition • 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.
• 6.
  Separate Declaration andDefinition • 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.
• 7.
  Write a programthat 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; } };
• 8.
  Write a programthat 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.
• 9.
  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.
• 10.
  Write a programthat 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; } };
• 11.
  Write a programthat 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(); }
• 12.
  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.
• 13.
  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();
• 14.
  • Static MemberFunction 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.
• 15.
  • Static membersare 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.
• 16.
  • // 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; • } • };
• 17.
  • // initializethe 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; • }