Re: Query: want a function that is called at initialisation time

From:

Greg Herlihy <greghe@mac.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 13 Dec 2007 17:34:01 CST

Message-ID:

<d0e847a4-d2ed-422b-99d6-639b66972049@d21g2000prf.googlegroups.com>

On Dec 12, 3:29 pm, tropostro...@hotmail.com wrote:

I have a class and I want a static member function of the class to run
at process initialisation time. What's the best way to do this? There
is a possible complication in that the class is templated. Here is my
current solution:

template<typename T> class Singleton
{ public:
  static void initialise( ) { . . . }

  static int dummy;
};

template<typename T> int Singleton<T>::dummy(
     Singleton<T>::initialise( ), 999);

main( )
{
    Singleton<MyClass> m;
}

At process initialisation, the static member Singleton<MyClass>::dummy
has to be initialised, and that causes the initialise( ) function to
be run before 999 is assigned to dummy. The problem is that this is
ugly. dummy serves no real purpose. Is there a better way?

One option would be to have initialize() return a result code - and
then store that result code in the (suitably renamed) "dummy"
variable:

    template<class T>
    class Singleton
    {
        static int initializeStatus;

    public:
        static int initialize( );
    };

    template<class T>
    int
    Singleton<T>::initializeStatus = Singleton<T>::initialize();

Now, in order to ensure that initialize() is actually called, it is
necessary to instantiate Singleton's "initializeStatus" static
variable. And the easiest way to do so, is to explicitly instantiate
the Singleton<MyClass> template class itself:

    template class Singleton<MyClass>; // explicit instantiation

    main( )
    {
        Singleton<MyClass> m;
    }

Greg

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