HP Integrity NonStop H-Series - Manual (Page 122)

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©Copyright 1996 Rogue Wave Software
The Priority Queue Operations
A priority queue is a data structure that can hold elements of type T and that implements the
following five operations:
push(T) add a new value to the collection being maintained
top() return a reference to the smallest element in collection
pop() delete the smallest element from the collection
size() return the number of elements in the collection
empty() return true if the collection is empty
Elements of type T must be comparable to each other, either through the use of the default less
than operator (the < operator), or through a comparison function passed either as a template
argument or as an optional argument on the constructor. The latter form will be illustrated in the
example program provided later in this section. As with all the containers in the Standard Library,
there are two constructors. The default constructor requires either no arguments or the optional
comparison function. An alternative constructor takes an iterator pair, and initializes the values in
the container from the argument sequence. Once more, an optional third argument can be used to
define the comparison function.
Initializing Queues from other containers
The priority queue data type is built on top of a container class, which is the structure actually
used to maintain the values in the collection. There are two containers in the standard library that
can be used to construct priority queues: vectors or deques.
Declaration and Initialization of priority queue
The following illustrates the declaration of several priority queues:
priority_queue< int, vector<int> > queue_one;
priority_queue< int, vector<int>, greater<int> > queue_two;
priority_queue< double, deque<double> >
queue_three(aList.begin(), aList.end());
priority_queue< eventStruct, vector<eventStruct> >
queue_four(eventComparison);
priority_queue< eventStruct, deque<eventStruct> >