Q:

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

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mahmoud2506
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2022-05-05
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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.

 

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mahmoud2506
2022-05-05
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Program:

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; 
    #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

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