Initialization of Data Members

In this tutorial, we'll look at how to initialise static member variables in C++. Static members, such as functions or variables, can be added to C++ classes. After declaring the class, we must initialise the static variables.

Class variables in C++ are initialised in the same sequence that they are listed in the class declaration.

Take a look at the code in the example below.

C++ Program:

#include<iostream>


using namespace std;


class Test {
private:	
	int b;
	int a;	
public:
	Test() : a (10), b (a + 10) {}
	void print ();
};


void Test::print()
{
cout<< "a = " << a << " b = " << b;
}


int main ()
{
	Test t;
	t.print ();
	getchar ();
	return 0;	
}

Output:

a = 10 b = 32777

Although b is initialised before a since it comes before a in the class declaration, the output contains some trash value for b instead of the correct value for a.

Therefore, to overcome the issue in the aforementioned code, use one of the two variants below.

C++ Code:

// Change the declarations order first.

class Date {
private:	
	int a;	
	int b;
public:
	Date () : a (10), b (a + 10) {}
	void print();
};

// Secondly Change the initialization order.

class Date {
private:	
	int a;
	int b;	
public:
	Date () : a (b-10), b (20) {}
	void print();
};