Re: curiosity singleton pattern?

From:
 James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 02 Aug 2007 07:11:28 -0000
Message-ID:
<1186038688.884388.96550@b79g2000hse.googlegroups.com>
On Aug 1, 11:06 am, Chris Forone <4...@gmx.at> wrote:

cant understand the following:

Scene* Scene::sole(0); // in Scene.cpp

class Scene // singleton in Scene.h
{
   public:
     static Scene* Get()
     {
       //return sole ? sole : new (std::nothrow) Scene;
       return sole; // for testing purposes only
     }

     int Print(void) // normaly only with valid objects?!
     {
       return reinterpret_cast<unsigned int>(sole);
       // other values also possible (return 10;)
     }

   protected:
     Scene();
     ~Scene();

   private:
     static Scene* sole;
};

int main(void)
{
   std::cout << Scene::Get() << std::endl;
   std::cout << Scene::Get()->Print() << std::endl;
}

returns

0
0

non static func Print is called by nullpointer?! have gcc 4.1
and linux os.


It's undefined behavior. Anything might happen. In practice,
on a modern general purpose machine, you will either get the
above results, or some sort of runtime error. Possibly
depending on the options you've passed to the compiler.

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