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;
pos = list.GetHeadPosition();
while (pos)
{
int nElement;
nElement = list.GetNext(pos);
}
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; TLListIter<int, int> iter(list);
iter.begin();
while (iter)
{
int nElement;
nElement = iter++;
}
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.