TREE(3)

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

SYNOPSIS
void
tree_init(void **tree);
void *
tree_srch(void **tree, int (*compare)(), void *data);
void
tree_add(void **tree, int (*compare)(), void *data, void (*del_uar)());
int
tree_delete(void **tree, int (*compare)(), void *data, void (*del_uar)());
int
tree_trav(void **tree, int (*trav_uar)());
void
tree_mung(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.