tsearch(3C)tsearch(3C)NAMEtsearch(), tfind(), tdelete(), twalk() - manage binary search trees
SYNOPSISDESCRIPTION
and are routines for manipulating binary search trees. They are gener‐
alized from Knuth (6.2.2) Algorithms T and D. All comparisons are done
with a user-supplied routine, compar. This routine is called with two
arguments, the pointers to the elements being compared. It returns an
integer less than, equal to, or greater than 0, according to whether
the first argument is to be considered less than, equal to or greater
than the second argument. The comparison function need not compare
every byte, so arbitrary data may be contained in the elements in addi‐
tion to the values being compared.
is used to build and access the tree. key is a pointer to an entry to
be accessed or stored. If there is an entry in the tree equal to the
value pointed to by key, a pointer to the previous key associated with
this found entry is returned. Otherwise, key is inserted, and a
pointer to it returned. Note that since the value returned is a
pointer to key and key itself is a pointer, the value returned is a
pointer to a pointer. Only pointers are copied, so the calling routine
must store the data. rootp points to a variable that points to the
root of the tree. A NULL value for the variable pointed to by rootp
denotes an empty tree; in this case, the variable is set to point to
the entry which will be at the root of the new tree.
Like searches for an entry in the tree, returning a pointer to it if
found. However, if it is not found, returns a NULL pointer. The argu‐
ments for are the same as for
deletes a node from a binary search tree. Arguments are the same as
for The variable pointed to by rootp is changed if the deleted node was
the root of the tree. returns a pointer to the parent of the deleted
node, or a NULL pointer if the node is not found.
traverses a binary search tree. root is the root of the tree to be
traversed. (Any node in a tree may be used as the root for a walk
below that node.) action is the name of a routine to be invoked at
each node. This routine is, in turn, called with three arguments:
· First argument is the address of the node being visited.
· Second argument is a value from an enumeration data type
(defined in the header file), depending on whether this is
the first, second or third time that the node has been vis‐
ited (during a depth-first, left-to-right traversal of the
tree), or whether the node is a leaf.
· Third argument is the level of the node in the tree, with the
root being level zero.
EXAMPLES
The following code reads strings, and stores structures containing a
pointer to each string and a count of its length. It then walks the
tree, printing out the stored strings and their lengths in alphabetical
order.
RETURN VALUE
A NULL pointer is returned by if there is not enough space available to
create a new node.
A NULL pointer is returned by and if rootp is NULL on entry.
If the datum is found, both and return a pointer to it. If not,
returns NULL, and returns a pointer to the inserted item.
WARNINGS
The root argument to is one level of indirection less than the rootp
arguments to and
Two nomenclatures are used to refer to the order in which tree nodes
are visited. uses preorder, postorder and endorder to respectively
refer to visiting a node before any of its children, after its left
child and before its right and after both its children. The alternate
nomenclature uses preorder, inorder, and postorder to refer to the same
visits, which could result in some confusion over the meaning of pos‐
torder. If the calling function alters the pointer to the root,
results are unpredictable.
SEE ALSObsearch(3C), hsearch(3C), lsearch(3C), thread_safety(5).
STANDARDS CONFORMANCEtsearch(3C)
