HP Integrity NonStop J-Series - Manual (Page 128)

Map-Based Iteration and Pairs
In the case of a map-based collection class, like RWMapVal, iterators refer to
instances of the Standard C++ Library structure pair. As you iterate over a map-based
collection, you have access to both the key and its associated data at each step along the traversal.
The pair structure provides members first and second, which allow you to individually access the
key and its data, respectively. For example:
typedef RWTValMap > Datebook;
Datebook birthdays;
// ... < populate birthdays collection >
Datebook::iterator iter = birthdays.begin();
while (iter != birthdays.end()) {
cout << (*iter).first // the key
<< " was born on "
<< (*iter).second // the data for that key
<< endl;
++iter;
};
Note that given a non-const reference to such a pair, you can still modify only the second
element_the data associated with the key. This is because the first element is declared to be of type
const K. Because the placement of objects within the collection class is maintained internally, based
on the value of the key, declaring it as const protects the integrity of the collection class. In order to
change a key within a map, you will have to remove the key and its data entirely, and replace them
with a new entry.
Iterators as Generalized Pointers
It may not be obvious at first, but you can think of an iterator as a generalized pointer. Imagine a
pointer to an array of ints. The array itself is a collection class, and a pointer to an element of that
array is a random-access iterator. To advance to the next element, you simply use the unary operator
++. To move back to a previous element, you use --. To access the element at the current position of
the iterator, you use the unary operator *. Finally, it is important to know when you have visited all
the elements. C++ guarantees that you can always point to the first address past the end of an
allocated array. For example:
int intCollection[10]; // an array of integers
// ... < put stuff in the array >
// position iter at start:
int* iter = intCollection;