singleton.hpp

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// PTF - Psychological Test Framework
// http://ptf.sourceforge.net
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Library General Public License for more details.
//
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

#ifndef __SINGLETON__
#define __SINGLETON__

#include <assert.h>

template<typename T> class Singleton{
private:
    static T* ms_singleton;
public:

    Singleton() {
        assert(!ms_singleton);
        // use a cunning trick to get the singleton pointing to the start of the 
        // whole, rather than the start of the Singleton part of the object
        int offset = (int)(T*)1 - (int)(Singleton <T>*)(T*)1;
        ms_singleton = (T*)((int)this + offset);
    }

    ~Singleton() {
        assert(ms_singleton);
        ms_singleton=0;
    }
 
    static T& getSingleton() {
        assert(ms_singleton);
        return *ms_singleton;
    }
    static T* getSingletonPtr() {
        assert(ms_singleton);
        return ms_singleton;
    }
};

template<typename T> T* Singleton<T>::ms_singleton = 0;

#endif

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