TREE(3)

NAME
tree_init, tree_mung, tree_srch, tree_add, tree_delete, tree_trav - balanced binary tree routines

SYNOPSIS
void
tree_init(tree)
void **tree;

void *
tree_srch(tree, compare, data)
void **tree;
int (*compare)();
void *data;

void
tree_add(tree, compare, data, del_uar)
void **tree;
int (*compare)();
void *data;
void (*del_uar)();

int
tree_delete(tree, compare, data, del_uar)
void **tree;
int (*compare)();
void *data;
void (*del_uar)();

int
tree_trav(tree, trav_uar)
void **tree;
int (*trav_uar)();

void
tree_mung(tree, del_uar)
void **tree;
void (*del_uar)();

DESCRIPTION
These functions create and manipulate a balanced binary (AVL) tree. Each node of the tree contains the expected left & right subtree pointers, a short int balance indicator, and a pointer to the user data. On a 32 bit system, this means an overhead of 4+4+2+4 bytes per node (or, on a RISC or otherwise alignment constrained system with implied padding, 4+4+4+4 bytes per node). There is no key data type enforced by this package; a caller supplied compare routine is used to compare user data blocks.

Balanced binary trees are very fast on searches and replacements, but have a moderately high cost for additions and deletions. If your application does a lot more searches and replacements than it does additions and deletions, the balanced (AVL) binary tree is a good choice for a data structure.

Tree_init creates an empty tree and binds it to tree (which for this and all other routines in this package should be declared as a pointer to void or int, and passed by reference), which can then be used by other routines in this package. Note that more than one tree variable can exist at once; thus multiple trees can be manipulated simultaneously.

Tree_srch searches a tree for a specific node and returns either NULL if no node was found, or the value of the user data pointer if the node was found. compare is the address of a function to compare two user data blocks. This routine should work much the way strcmp(3) does; in fact, strcmp could be used if the user data was a NUL terminated string. data is the address of a user data block to be used by compare as the search criteria. The tree is searched for a node where compare returns 0.

Tree_add inserts or replaces a node in the specified tree. The tree specified by tree is searched as in tree_srch, and if a node is found to match data, then the del_uar function, if non-NULL, is called with the address of the user data block for the node (this routine should deallocate any dynamic memory which is referenced exclusively by the node); the user data pointer for the node is then replaced by the value of data. If no node is found to match, a new node is added (which may or may not cause a transparent rebalance operation), with a user data pointer equal to data. A rebalance may or may not occur, depending on where the node is added and what the rest of the tree looks like. Tree_add will return the data pointer unless catastrophe occurs in which case it will return NULL.

Tree_delete deletes a node from tree. A rebalance may or may not occur, depending on where the node is removed from and what the rest of the tree looks like. Tree_delete returns TRUE if a node was deleted, FALSE otherwise.

Tree_trav traverses all of tree, calling trav_uar with the address of each user data block. If trav_uar returns FALSE at any time, tree_trav will immediately return FALSE to its caller. Otherwise all nodes will be reached and tree_trav will return TRUE.

Tree_mung deletes every node in tree, calling del_uar (if it is not NULL) with the user data address from each node (see tree_add and tree_delete above). The tree is left in the same state that tree_init leaves it in - i.e., empty.

BUGS
Should have a way for the caller to specify application specific malloc and free functions to be used internally when allocating meta data.

AUTHOR
Paul Vixie, converted and augumented from Modula-2 examples in Algorithms & Data Structures, Niklaus Wirth, Prentice-Hall, ISBN 0-13-022005-1.