HP Integrity NonStop J-Series - Manual (Page 93)

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©Copyright 1996 Rogue Wave Software
Chapter 9: Using Class
RWBTreeOnDisk
Construction ❍
Example ❍
Class RWBTreeOnDisk has been designed to manage a B-tree in a disk file. The class
represents an ordered collection of associations of keys and values, where the ordering is
determined internally by comparing keys. Given a key, a value can be retrieved. Duplicate keys
are not allowed.
Keys are arrays of char. The key length is set by the constructor. The ordering in the B-tree is
determined by comparing keys with an external function, which you can change.
The type of the values is:
typedef long RWstoredValue;
The values typically represent an offset to a location in a file where an object is stored. Given a
key, you can find where an object is stored and retrieve it. As far as class
RWBTreeOnDisk is
concerned, however, the value has no special meaning_it is up to you to interpret it.
The class RWBTreeOnDisk uses class RWFileManager to manage the allocation and
deallocation of space for the nodes of the B-tree. You can use the same RWFileManager to
manage the space for the objects themselves if the B-tree and data are to be in the same file.
Alternatively, you could use a different RWFileManager, managing a different file, to store the
B-tree and data in separate files.
The member functions associated with class RWBTreeOnDisk are similar to those of the
in-memory class RWBTreeDictionary , except that keys are arrays of char rather than
RWCollectable s. There are member functions to add a key-value pair, remove a pair, replace a
value associated with a key, query for information associated with a key, operate on all
key-value pairs in order, return the number of entries in the tree, and determine if a key is
contained in the tree.