Static class object

Question

Why are static class objects allowed in C++? what is their use?

#include<iostream>

using namespace std;

class Test {
  static Test self;  // works fine

  /* other stuff in class*/

};

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

Answer 1

This just works; the compiler doesn't have to do anything special simply because self is both a static member of Test and is of type Test. I see no reason why this special case would need to be specifically prohibited.

Now, there is a problem with Test::self in that you declare the variable, but fail to define it. However, this is simply a bug in your code and is easily fixed:

class Test {
  ...
};

Test Test::self; // <--- the definition

int main()
{
  ...

Answer 2

You use it for things that are shared between all instances of the class. For example, you can use it to implement the Singleton pattern.