Example of Static Data Members

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The following example shows the declaration, initialization, use, and scope of the static data member si and static member functions Set_si(int) and Print_si().

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// This example shows the declaration, initialization,
// use, and scope of a static data member.

#include <iostream.h>
class X
{
      int i;
      static int si;
public:
      void Set_i(int i) { this->i = i; }
      void Print_i() { cout << "i = " << i << endl; }
      // Equivalent to:
      // void Print_i(X* this)
      // { cout << "X::i = " << this->i << endl; }
      static void Set_si(int si) { X::si = si; }

      static void Print_si()
      {
            cout << "X::si = " << X::si << endl;
      }
      // Print_si doesn't have a 'this' pointer
};
int X::si = 77;       // Initialize static data member

void main()
{
      X xobj;
      // Non-static data members and functions belong to specific
      // instances (here xobj) of class X
      xobj.Set_i(11);
      xobj.Print_i();

      // static data members and functions belong to the class and
      // can be accessed without using an instance of class X
      X::Print_si();
      X::Set_si(22);
      X::Print_si();
}

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This example produces the following output:

i = 11
X::si = 77
X::si = 22

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