CList Iterator

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Introduction

MFC's CList provides a template linked list implementation and works perfectly adequately. However, iterating through the list can be a little combersome. Code like that below is common place for processing list elements, but the POSITION variable is meaningless and confusing as it always points to the next node rather than the current one.

POSITION        pos;
CList<int, int> list;

// add nodes to the list


pos = list.GetHeadPosition();
while (pos)
{
    int nElement;

    nElement = list.GetNext(pos);
    // do something with nElement

}

TLListIter class

The iterator class I present here simplifies the use slightly, making the code easier to read and maintain. It originates from a larger project I wrote where I have a list of objects of type A, each with their own list of objects of type B, and I needed to iterate all objects of type B in the system. This class simplified the task immensly.

So using this class, the above code becomes

CList<int, int>      list;		// linked list

TLListIter<int, int> iter(list);	// linked list iterator

// add nodes to the list


iter.begin();
while (iter)
{
    int nElement;

    nElement = iter++;
    // do something with nElement

}

Public Members

Construction/Destruction

TLListIter(TLList<TYPE, ARG_TYPE> &__list);
Constructor to initialise the iterator with the the linked list to be iterated.

TLListIter(TLListIter<TYPE, ARG_TYPE> &__iter);
Copy constructor to create a new iterator for the same linked list with the same node position.

virtual ~TLListIter();
Virtual class destructor.

Operators

operator bool ();
Boolean operator will return true if there is a current node, or false if not.

operator ARG_TYPE ();
Linked List argument operator will returns the element at the current node.

Navigation

TLListIter<TYPE, ARG_TYPE> operator++(int);
Post increment operator returns the current node and moves the internal position to the next node.

TLListIter<TYPE, ARG_TYPE> operator--(int);
Post decrement operator returns the current node and moves the internal position to the previous node.

// these functions will return false if there are no elements in the list

bool begin(void);
Moves to the first node in the list. This function returns false if the linked list is empty.

bool end(void);
Moves to the last node in the list. This function returns false if the linked list is empty.

MFC Compatibilty

POSITION GetPosition(void) const;

Returns the internal POSITION variable.

Limitations

• As the class stands, it cannot be used to process a list of bool. This is because of the operator bool() used to determine the end of the list.
• For some reason unknown to me (please let me know any solutions) a compiler error is generated if the class is used while (nNumber == 7 && iter). Instead, this must be coded while (nNumber == 7 && iter == true) and then all is fine. Wierd.

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I'm translating the article julianico 5:14 20 Dec '05   Hello, I would like to know if I can translate articles including references in the header,i. e.: Articulo original en la pagina http://www.codeproject.com/cpp/clist_iter.asp Autor del articulo original: Craig Henderson Traducción por: Julián Iniesta and there's no problem if I upload this to the site albacete.dotnetclubs.com. We are a group of spanish students. I would like to tell this to Craig, but i have no idea how to get his email. I wait your answers, if you say it,s not possible, I won´t upload the translated article. Thanks -- modified at 10:14 Tuesday 20th December, 2005 Sign In·View Thread·PermaLink My diff List Anonymous 23:25 30 Dec '03   hello I want creat a list where you find a pointer to another list ... ____ ____ |:(:(|---|;P;P|... ---- ---- | ____ |--| |... ---- Sign In·View Thread·PermaLink My diff List Anonymous 23:23 30 Dec '03   hello I want creat a list where you find a pointer to another list ... ____ ____ | |---| |... ---- ---- | ____ |--| |... ---- Sign In·View Thread·PermaLink Iterator Andre Pham 9:28 29 Dec '03   Hello Below is my code about List Iterator. It is ok when i compile it. But when i try to build it. the following errors come up. "DoubleOrderedLinkedList.obj : error LNK2019: unresolved external symbol "public: int __thiscall ListIterator::getNext(void)" (?getNext@?$ListIterator@H@@QAEHXZ) referenced in function _main" Could any body here help me solve this problem? Thanks, Andre ------------------------------------------------ template class DoubleOrderedLinkedList; template class ListIterator; template class Node { Object data; Node * next; Node * prev; Node(const Object& newItem) : data (newItem), next (0), prev (0) {} friend DoubleOrderedLinkedList<Object>; friend ListIterator<Object>; }; template class DoubleOrderedLinkedList { Node<Object>* head; int numItems; public: DoubleOrderedLinkedList(); ~DoubleOrderedLinkedList(); int size() const; void Insert(const Object&); void Remove(const Object&); void Purge(); void displayList() const; ListIterator<Object> Iterator() const; friend ListIterator<Object>; }; template class ListIterator { int pos; Node<Object>* curr; public: ListIterator(Node<Object>* const); bool hasNext() const; Object getNext(); bool hasPrevious() const; Object getPrevious(); }; #include #include "DoubleOrderedLinkedList.h" #include "ListIterator.h" using namespace std; template DoubleOrderedLinkedList<Object>::DoubleOrderedLinkedList() : head (0), numItems (0) {} template DoubleOrderedLinkedList<Object>::~DoubleOrderedLinkedList() {} template DoubleOrderedLinkedList<Object>::size() const { return numItems; } template ListIterator<Object> DoubleOrderedLinkedList<Object>::Iterator() const { ListIterator<Object> it (head); return it; } template void DoubleOrderedLinkedList<Object>::Insert(const Object& x) { Node<Object>* previous = 0; Node<Object>* curr = head; while ((curr != 0) && (curr->data < x)) { previous = curr; curr = curr->next; } Node<Object> * const newNode = new Node<Object> (x); if (head == 0) { head = newNode; } else { if (curr == head) { newNode->next = curr; curr->prev = newNode; head = newNode; } else { if (curr != 0) { newNode->next = curr; newNode->prev = curr->prev; curr->prev->next = newNode; curr->prev = newNode; } else { newNode->prev = previous; previous->next = newNode; } } } numItems++; } template void DoubleOrderedLinkedList<Object>::displayList() const { Node<Object>* ptr = head; cout << "[ "; while (ptr != 0) { cout << ptr->data << " "; ptr = ptr->next; } cout << " ]" << endl; } int main() { DoubleOrderedLinkedList l; l.Insert(10); l.Insert(5); l.Insert(15); l.displayList(); ListIterator it = l.Iterator(); cout << "Testing Iterator" << endl; while (it.hasNext()) { cout << it.getNext() << endl; } } #include "DoubleOrderedLinkedList.h" #include "ListIterator.h" template ListIterator<Object>::ListIterator(Node<Object>* const p) : pos (0), curr (p) {} template bool ListIterator<Object>::hasNext() const { return (pos < numItems); } template Object ListIterator<Object>::getNext() { if (hasNext()) { Object item = curr->data; if (curr->next != 0) { curr = curr->next; } pos++; return item; } else { //throw(Exception("No Such Element"); } } template bool ListIterator<Object>::hasPrevious() const { return (pos > 0); } template Object ListIterator<Object>::getPrevious() { if (hasPrevious()) { if ((curr.prev != 0) && (pos < numItems)) { curr = curr->prev; } Object item = curr->data; pos--; return item; } else { //throw(Exception("No Such Element"); } } Sign In·View Thread·PermaLink POSITION RAyRAy 16:34 26 May '02   I have my own program I'm writing using MFC's CList. I'm trying to use Position, but for some reason it doesn't know what kind of data type there is. Is there a header file? I've already include afxtempl.h or something like that for collections Sign In·View Thread·PermaLink 1.00/5 (2 votes) code source seems not ok Luc Vandal 12:03 20 Nov '00   It seems that there's something missing from the code source, like the constructor or something because it's not working at all in my project... it won't even compile! Sign In·View Thread·PermaLink 3.00/5 (2 votes) Re: code source seems not ok Craig Henderson 5:19 1 Dec '00   Can you post some example code. It works fine in several of my own projects, so I need to see how you are using it. Sign In·View Thread·PermaLink 1.67/5 (2 votes)

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