Tools.h++ Manual

104011 Tandem Computers Incorporated 21-43
21
RWBTreeOnDisk
Synopsis typedef long RWstoredValue;
typedef int (*RWdiskTreeCompare)(const char*,
const char*,
size_t);
#include <rw/disktree.h>
#include <rw/filemgr.h>
RWFileManager fm(”filename.dat”);
RWBTreeOnDisk bt(fm);
Description Class RWBTreeOnDisk represents an ordered collection of associations of keys
and values, where the ordering is determined by comparing keys using an
external function. The user can set this function. Duplicate keys are not
allowed. Given a key, the corresponding value can be found.
This class is specifically designed for managing a B-Tree in a disk file. Keys,
defined to be arrays of chars , and values, defined by the typedef
RWstoredValue , are stored and retrieved from a B-Tree. The values can
represent offsets to locations in a file where objects are stored.
The key length is set by the constructor. By default, this value is 16 characters.
By default, keys are null-terminated. However, the tree can be used with
embedded nulls, allowing multibyte and binary data to be used as keys. To do
so you must:
• Specify TRUE for parameter ignoreNull in the constructor (see below);
• Make sure all buffers used for keys are at least as long as the key length
(remember, storage and comparison will not stop with a null value);
• Use a comparison function (such as memcmp() ) that ignores nulls.
This class is meant to be used with class RWFileManager which manages the
allocation and deallocation of space in a disk file.
When you construct an RWBTreeOnDisk you give the location of the root node
in the constructor as argument start . If this value is RWNIL (the default) then
the location will be retrieved from the RWFileManager using function
start() (see class RWFileManager ). You can also use the enumeration