Understanding Static Data Members and Functions in C++

1. Department of Computer and Information Science,School of Science, IUPUI ClassesStatic Members CSCI 240 Dale Roberts, Lecturer Computer Science, IUPUI E-mail: droberts@cs.iupui.edu

2. Static Members • Data and Functions Can be static • Exists Independently of Any Instantiated Objects

3. Static Data Members • COMMON to All the Objects of that Class • Exist Even When NO Class Objects Exist • Definition for static Data Members is a Declaration in header file • Initialization ONLY by an Initializer or an Assignment Statement inside a static member function • Accessing -- class_name::data_name or object_name.data_name

4. Static Data Members -- Example • // student.h#define size 20 class student{ char *name, *ss; static char *instructor; public: student(char *, char *); ~student();};

5. Static Data Members – Example (cont) • // student.cpp#include “student.h”#include <iostream>student::student(char *ip_name, char *ip_ss){ name = new char[size]; ss = new char[size]; strcpy(name, ip_name); strcpy(ss, ip_ss);} void student::print(){ cout << "Name: " << name << endl; cout << "SS: " << ss << endl; cout << "Instructor: " << instructor << endl;} }; /* Definition and Initialization of Static member */ char *student::instructor = "Henry";

6. Static Data Members -- Example • // client.cpp#include “student.h”main() { student s1("John", "012345678"); student s2("Tom", "999999999"); s1.print(); s2.print();} • Name: John SS: 012345678 Instructor: Henry Name: TomSS: 999999999 Instructor: Henry  

7. Static Member Functions • COMMON to All Objects of the Class • Created by the Class Definition -- Exist Even when NO Class Objects Exist • Can Only Access Static Data Members of the Class or other static member functions • Accessing -- class_name::function_name() or object_name.function_name()

8. Static Member Functions -- Example • // student.h#define size 20 class student{ char *name; char *ss; static char *instructor; public: student(char *ip_name, char *ip_ss); static void print_instructor(); };

9. Static Member Functions – Example (cont) • // student.cpp#include “student.h”#include <iostream>student::student(char *ip_name, char *ip_ss){ name = new char[size]; ss = new char[size]; strcpy(name, ip_name); strcpy(ss, ip_ss);} static void student::print_instructor() { cout << "Instructor: " << instructor << endl;} /* Definition and Initialization of Static member */ char *student::instructor = "Henry";

10. Static Member Functions – Example (cont) • // client.cpp#include “student.h”main() { student::print_instructor();} • Output will be: Instructor: Henry Notice that no instance of student is required.

11. Acknowledgements • These slides were originally prepared by Rajeev Raje, modified by Dale Roberts.