Added SharedPtr class.

include/SharedPtr.h

+/***************************************************************************
+                          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