Home » C++ programs » C++ class and object programs

Count the created objects using static member function in C++

Here, we are going to learn by a program how to count the created objects using static member function in C++?
Submitted by IncludeHelp, on September 14, 2018 [Last updated : March 01, 2023]

Static data member

A static data member is also known as "Class Member" and it is available for all classes. In other words – we can say "A static data member is just like a global variable for a class". Generally, static data members are used to maintain the common things related to the class, like counting the objects etc.

Static Member Function

A static member function is used to access or manipulate the static data member, other data member cannot be used with a static member function.

Logic to count the created objects using static member function

This program is implemented to count the total number of created objects with the help of static data member and static member function.

• A static data member needs to be declared first that we declared in private section: Example: static int count;
• To count the object, data member count must be incremented by 1, that we have done in the constructor because the constructor is invoked when a new object is created.
• To print the total number of created objects, we created a static member function named totalObjects() which is returning the value of count.
• Final and important thing – A static data member must be initialized outside of the class with the class name. Example: int Message::count =0;

C++ program to count the created objects using static member function

#include <iostream>
#include <string.h>
using namespace std;

class Message {
private:
    char str[30];
    //static data member to count the objects
    static int count;

public:
    //constructor
    Message()
    {
        count++;
    }

    //member function to initialise message
    void initMessage(char s[])
    {
        strcpy(str, s);
    }

    //member function to print message
    void printMessage(void)
    {
        cout << str << endl;
    }

    //static member function
    static int totalObjects(void)
    {
        return count;
    }
};

//initialise static member function
int Message::count = 0;

//main function
int main()
{
    Message M1;
    Message M2;
    Message M3;

    M1.initMessage("Message one");
    M2.initMessage("Message two");
    M3.initMessage("Message three");

    M1.printMessage();
    M2.printMessage();
    M3.printMessage();

    //printing object count
    cout << "Total objects created: " << Message::totalObjects() << endl;

    return 0;
}

Output

Message one
Message two
Message three
Total objects created: 3