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operator ++/-- overloading in templates

harmless · 2007-08-05T20:01:02

Hello fellas, I have implemented a linked list class using template and so far it's been working nicely. But now i added a feature that can iterate thru the items in the list and i used the operators ++ and -- to iterate from top-to-bottom and bottom-to-top of the list respectively. My implementation is shown below: template < typename TYPE > class TLinkedList { private: // element structure with a pointer to its next/prev link (double linked list) struct Element { TYPE Data; Element* pNext; Element* pPrev; Element( void ) { pNext = NULL; pPrev = NULL; } virtual ~Element( void ) {} }; // pointer to the linked list's top/bottom element in the list Element* pHead; Element* pIterate; public: TLinkedList( void ); // done virtual ~TLinkedList( void ){ } // done void operator++( void ); // done void operator++( int ); // done void operator--( void ); // done void operator--( int ); // done }; template < typename TYPE > void TLinkedList< TYPE >::operator++( void ) { if ( CanIterate() ) { pIterate = pIterate->pNext; } } template < typename TYPE > void TLinkedList< TYPE >::operator++( int ) { if ( CanIterate() ) { pIterate = pIterate->pNext; } } template < typename TYPE > void TLinkedList< TYPE >::operator -- ( void ) { if ( CanIterate() ) { pIterate = pIterate->pPrev; } } template < typename TYPE > void TLinkedList< TYPE >::operator -- ( int ) { if ( CanIterate() ) { pIterate = pIterate->pPrev; } } If say i created a list for a type int: TLinkedList < int > i_list; calling i_list++ or i_list-- works just fine. However, if i now created a pointer to a list for type int: TLinkedList < int >* i_plist = new TLinkedList < int >; and call i_plist++ or i_plist--, my program crashes. I can see the problem here is that because i_plist is a pointer, the operator ++/-- tends to see i_plist as a pointer, and not a TLinkedList <int> causing it to perform its normal operation for pointers rather than the overloaded function defined in TLinkedList <int>. Is there any way to make the overloaded ++/-- operators be called even if i use those operators on pointers to list? Thanks in advance! Cheers! EDIT: Oh and btw, i'm by no means a c++ guru. So if you see any wierd or funny stuff in my code up there, feel free to bash at will. [Edited by - harmless on August 5, 2007 1:16:18 AM]

General and Gameplay Programming Programming

Started by harmless August 05, 2007 12:27 AM

9 comments, last by Jaiminho 16 years, 8 months ago

Jaiminho

184

August 05, 2007 08:01 PM

Quote:Original post by harmless
ah yes, the idea of having more than one iterator is nice. I would love to implement an iterator class, is there any good links that you know of that i can reference to in order to implement one?

Iterators classes are simply wrapped pointers. You have a pointer to your element (in this case, the list node) which is set to point to this->pNext and this->pPrev with the operators ++ and --. Aside from that, you need operators to compare (basically, only == and !=) the used iterator with one returned by a list method and an access operator to retrieve the data contents of the node, usually with unary operator * (you don't return a reference to the node, but a reference to the data). Of course, there are lots of complications and improvements done on std::list, but the basic is simply that.

You can google for the interface on std::list to check how it actually works. Anyway...

Quote:Original post by osmanb
Step away from the keyboard and go think about a more interesting programming problem.

Yes, it is a quite too simple programming problem.

operator ++/-- overloading in templates

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