TSEARCH(3)

NAME
tdelete, tfind, tsearch, twalk - manipulate binary search trees

SYNOPSIS
#include <search.h>
void *
tdelete(const void *restrict key, void **restrict rootp, int (*compar) (const void *key1, const void *key2));
void *
tfind(const void *key, void *const *rootp, int (*compar) (const void *key1, const void *key2));
void *
tsearch(const void *key, void **rootp, int (*compar) (const void *key1, const void *key2));
void
twalk(const void *root, void (*action) (const void *node, VISIT order, int level));

DESCRIPTION
The tdelete(), tfind(), tsearch(), and twalk() functions manage binary search trees, based on algorithms T and D from Knuth (6.2.2). The comparison function passed in by the user takes two arguments, each of which is a key pointer. This function has the same style of return values as strcmp(3).

The tfind() function searches for a node whose key matches the argument key in the binary tree rooted at rootp, returning a pointer to the node if it is found and NULL if it is not.

Note that a node is itself a pointer to the key of the node. Thus, you should generally cast this result to a double pointer to the data type stored in the tree, for example (struct myType **), and use double indirection to retrieve the original key value.

The tsearch() function is identical to tfind() except that, if no match is found, it inserts a new node for the key into the tree and returns a pointer to the node. If rootp points to a NULL value, a new binary search tree is created.

The tdelete() function deletes a node from the specified binary search tree and returns a pointer to the parent of the node that was deleted. It takes the same arguments as tfind() and tsearch(). If the node to be deleted is the root of the binary search tree, rootp will be adjusted.

The twalk() function walks the binary search tree rooted in root and calls the function action on each node. The action function is called with three arguments: a pointer to the current node, a value from the enum typedef enum { preorder, postorder, endorder, leaf } VISIT; specifying the traversal type, and a node level (where level zero is the root of the tree).

As twalk() traverses the tree, it calls the action function with the traversal type "preorder" before visiting the left subtree of the node, with the traversal type "postorder" before visiting the right subtree of the node, and with the traversal type "endorder" after visiting the right subtree of the node. The action function is called only once for a leaf-node, with the traversal type "leaf."

Note: the names for the traversal types differ somewhat from common parlance. The traversal type "postorder" corresponds to what would typically be referred to as in-order, and the traversal type "endorder" corresponds to what would typically be referred to as post-order.

RETURN VALUES
The tsearch() function returns NULL if allocation of a new node fails (usually due to a lack of free memory).

The tfind(), tsearch(), and tdelete() functions return NULL if rootp is NULL or the node cannot be found.

The twalk() function returns no value.

SEE ALSO
bsearch(3), hsearch(3), lsearch(3)