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Smart Pointer Class

Tuesday, July 13, 2004 by digitalpeer, updated Wednesday, August 18, 2004

Smart pointers were the latest craze awhile back, but in my opinion are sometimes more trouble than their worth. The idea is to use pointers and never have to de-allocate what they are pointing to. They use reference counting to delete the object when the pointer finally goes out of scope.

This is a simple "smart pointer" class I wrote that might help assist you in developing your own or even understanding how they work.

#ifndef SMARTPTR_H
#define SMARTPTR_H

#include <cassert>
using namespace std;

template <typename type>
class smartptr
{
	public:
		smartptr(type* ptr = 0);
		smartptr(const smartptr<type>& orig);
		~smartptr();

		type* operator->() const;
		type& operator*() const;
		smartptr<type>& operator=(const smartptr<type>& rhs);


	private:
		/* The pointer to the object we created */
		type* thePointer_;
		/* The number of instances pointing to this pointer */
		int* count_;
		
		void doDelete();
};

template <typename type>
smartptr<type>::smartptr(type* ptr):thePointer_(ptr), count_(new int)
{
	*count_ = 1;
}

template <typename type>
smartptr<type>::smartptr(const smartptr<type>& orig):thePointer_(orig.thePointer_)
{
	count_ = orig.count_;
	thePointer_ = orig.thePointer_;
	++(*count_);
}

template <typename type>
smartptr<type>::~smartptr()
{
	doDelete();
}

template <typename type>
type* smartptr<type>::operator->() const
{
	return thePointer_;
}

template <typename type>
type& smartptr<type>::operator*() const
{
	assert(thePointer_ != 0);
	return *thePointer_;
}

template <typename type>
smartptr<type>& smartptr<type>::operator=(const smartptr<type>& rhs)
{
	/* check for a=a */
	if (this != &rhs)
	{
		doDelete();
		count_ = rhs.count;
	}

	return *this;
}

template <typename type>
void smartptr<type>::doDelete()
{
	assert(*count_ != 0);
	*count_ = *count_ - 1;
	if (*count_ == 0)
	{
		delete thePointer_;
		delete count_;
	}
}

#endif