Re: newbie question on singleton class

Gianni Mariani <>
12 May 2007 17:11:17 -0700
On May 12, 11:53 pm, wrote:

I liked this article by Danny Kalev on the singleton design class:

However I was confused by this:

The class's implementation looks like this:

  Singleton* Singleton::pinstance = 0;// initialize pointer
  Singleton* Singleton::Instance ()
    if (pinstance == 0) // is it the first call?
      pinstance = new Singleton; // create sole instance
    return pinstance; // address of sole instance

A much easier way to write this is:

   Singleton* Singleton::Instance ()
      static Singleton* pinstance = new Singleton;
      return pinstance; // address of sole instance

This will also generate thread safe code on some compilers.

So I would have thought that Singleton* Singleton::pinstance = 0;
violates private access.

The initialization expression is in the scope of the class. i.e.

class foo
    static const unsigned int x = 1;

    static unsigned int y;

unsigned int foo::y = x; // note not foo::x - just x

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