Understanding Static Data Members in Object-Oriented Programming, Slides of Object Oriented Programming

Download Understanding Static Data Members in Object-Oriented Programming and more Slides Object Oriented Programming in PDF only on Docsity! Object Oriented Programming (OOP) I -TomU ldo \ (0m Review ►Constant data members ►Constant objects ►Static data members docsity.com Class vs. Instance Variable ►Student s1, s2, s3; Class Space s1(rollNo,…) s2(rollNo,…) s3(rollNo,…) Instance Variable Class Variable docsity.com Static Data Member (Syntax) ►Keyword static is used to make a data member static class ClassName{ … static DataType VariableName; }; docsity.com Defining Static Data Member ►Static data member is declared inside the class ►But they are defined outside the class docsity.com Example class Student{ private: static int noOfStudents; public: … }; int Student::noOfStudents = 0; /*private static member cannot be accessed outside the class except for initialization*/ docsity.com Initializing Static Data Member ►If static data members are not explicitly initialized at the time of definition then they are initialized to 0 docsity.com Example int Student::noOfStudents; is equivalent to int Student::noOfStudents=0; docsity.com Life of Static Data Member ►They are created even when there is no object of a class ►They remain in memory even when all objects of a class are destroyed docsity.com Example class Student{ public: static int noOfStudents; }; int Student::noOfStudents; int main(){ Student::noOfStudents = 1; } docsity.com Example class Student{ public: static int noOfStudents; }; int Student::noOfStudents; int main(){ { Student aStudent; aStudent.noOfStudents = 1; } Student::noOfStudents = 1; } docsity.com Example class Student{ … public: static int noOfStudents; Student(); ~Student(); … }; int Student::noOfStudents = 0; docsity.com Example Student::Student(){ noOfStudents++; } Student::~Student(){ noOfStudents--; } docsity.com Example int Student::noOfStudents = 0; int main(){ cout <<Student::noOfStudents <<endl; Student studentA; cout <<Student::noOfStudents <<endl; Student studentB; cout <<Student::noOfStudents <<endl; } Output: 0 1 2 docsity.com Static Member Function ►They are used to access static data members ►Access mechanism for static member functions is same as that of static data members ►They cannot access any non-static members docsity.com Example class Student{ static int noOfStudents; int rollNo; public: static int getTotalStudent(){ return noOfStudents; } }; int main(){ int i = Student::getTotalStudents(); } docsity.com Accessing non static data members int Student::getTotalStudents(){ return rollNo; } int main(){ int i = Student::getTotalStudents(); /*Error: There is no instance of Student, rollNo cannot be accessed*/ } docsity.com Array of Objects ►Array of objects can only be created if an object can be created without supplying an explicit initializer ►There must always be a default constructor if we want to create array of objects docsity.com Example class Test{ public: }; int main(){ Test array[2]; // OK } docsity.com Example class Test{ public: Test(); }; int main(){ Test array[2]; // OK } docsity.com