HP Integrity NonStop J-Series - Manual (Page 108)

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©Copyright 1996 Rogue Wave Software
Iterators in Collection Classes
Many of the collection classes have an associated iterator. The advantage of the iterator is that it
maintains its own internal state, thus allowing two important benefits:
More than one iterator can be constructed from the same collection class; ●
All of the items need not be visited in a single sweep. ●
Iterators are always constructed from the collection class itself, as in the following example:
RWBinaryTree bt;
.
.
.
RWBinaryTreeIterator bti(bt);
Immediately after construction, or after reset()is called, the state of the iterator is undefined.
You must either advance it or position it before using its current state or position.
For traditional Tools.h++ iterators_those declared as a distinct class related to the collection
class_the rule is "advance and then return."
[10] However, iterators obtained directly from
classes implemented using the Standard C++ Library differ. In keeping with the standard for
container classes, they follow the precept: If you obtain an iterator using the begin() or end()
method, or using an algorithm which returns an iterator, you have a "Standard Library"
iterator.
[11] A Standard Library iterator must always be compared against that collection's end()
iterator to discover if it references an item in the container.
Traditional Tools.h++ Iterators
Traditional Tools.h++ iterators have a number of unique features.
You recall that the state of the iterator is undefined immediately following construction or the
calling of reset(). You also trigger the undefined state if you change the collection class
directly
[12] by adding or deleting objects while an iterator is active. Using an iterator at that
point can bring unpredictable results. You must then use the member function reset() to restart
the iterator, as if it had just been constructed.
At any given moment, the iterator marks an object in the collection class_think of it as the