Added SharedPtr class.

/***************************************************************************

                          SharedPtr.h

                        -------------------

    begin                : Fri Dec 20 2013

    copyright            : (C) 2013 by Andrea Zoli

    email                : zoli@iasfbo.inaf.it

 ***************************************************************************/

/***************************************************************************

 *                                                                         *

 *   This program is free software for non commercial purpose              *

 *   and for public research institutes; you can redistribute it and/or    *

 *   modify it under the terms of the GNU General Public License.          *

 *   For commercial purpose see appropriate license terms                  *

 *                                                                         *

 ***************************************************************************/

#ifndef _SHARED_PTR_H

#define _SHARED_PTR_H

namespace PacketLib

{

template<class T>

class SharedPtr

{

	template<class U>

	friend class SharedPtr;

	public:

	SharedPtr() : p(0), c(0) {}

	explicit SharedPtr(T* s) : p(s), c(new unsigned(1)) {}

	SharedPtr(int null) : p(0), c(0) {}

	SharedPtr(const SharedPtr& s) : p(s.p), c(s.c) { if(c) ++*c; }

	template<class U>

	SharedPtr(const SharedPtr<U>& s) : p(s.p), c(s.c) { if(c) ++*c; }

	~SharedPtr() { clear(); }

	SharedPtr& operator=(const SharedPtr& s)

	{ if(this!=&s) { clear(); p=s.p; c=s.c; if(c) ++*c; } return *this; }

	typedef T* SharedPtr<T>::*unspecified_bool_type;

	operator unspecified_bool_type() const // never throws

	{

		return p == 0 ? 0 : &SharedPtr<T>::p;

	}

	void clear()

	{

		if(c)

		{

		    if(*c==1) delete p;

		    if(!--*c) delete c;

		}

		c=0; p=0;

	}

	T* get() const { return (c)? p: 0; }

	T* operator->() const { return get(); }

	T& operator*() const { return *get(); }

	private:

	T* p;

	unsigned* c;

};

}

#endif