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CList Iterator

, 12 Oct 2000 CPOL
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A simple iteration class for MFC's CList linked list.

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.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Craig Henderson
Technical Lead
United Kingdom United Kingdom
Craig graduated with a B.SC. Honours in Computing for Real Time Systems from the University of the West of England, Bristol in 1995 after completing an HND in Computing in 1993.
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Comments and Discussions

 
GeneralI'm translating the article Pinmemberjulianico20-Dec-05 5:14 
GeneralMy diff List PinsussAnonymous30-Dec-03 23:25 
GeneralMy diff List PinsussAnonymous30-Dec-03 23:23 
GeneralIterator PinmemberAndre Pham29-Dec-03 9:28 
GeneralPOSITION PinmemberRAyRAy26-May-02 16:34 
Generalcode source seems not ok PinmemberLuc Vandal20-Nov-00 12:03 
GeneralRe: code source seems not ok PinmemberCraig Henderson1-Dec-00 5:19 

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