TSEARCH(3C) Standard C Library Functions TSEARCH(3C)


tsearch, tfind, tdelete, twalk - manage binary search trees


#include <search.h>

void *tsearch(const void *key, void **rootp,
int (*compar)(const void *, const void *));

void *tfind(const void *key, void * const *rootp,
int (*compar)(const void *, const void *));

void *tdelete(const void *restrict key, void **restrict rootp,
int (*compar)(const void *, const void *));

void twalk(const void *root, void(*action) (void *, VISIT, int));


The tsearch(), tfind(), tdelete(), and twalk() functions are routines for
manipulating binary search trees. They are generalized from Knuth
(6.2.2) Algorithms T and D. All comparisons are done with a user-supplied
routine. 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 addition to the values being compared.

The tsearch() function is used to build and access the tree. The key
argument is a pointer to a datum to be accessed or stored. If there is a
datum in the tree equal to *key (the value pointed to by key), a pointer
to this found datum is returned. Otherwise, *key is inserted, and a
pointer to it returned. Only pointers are copied, so the calling routine
must store the data. The rootp argument 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 will be set to
point to the datum which will be at the root of the new tree.

Like tsearch(), tfind() will search for a datum in the tree, returning a
pointer to it if found. However, if it is not found, tfind() will return
a null pointer. The arguments for tfind() are the same as for tsearch().

The tdelete() function deletes a node from a binary search tree. The
arguments are the same as for tsearch(). The variable pointed to by
rootp will be changed if the deleted node was the root of the tree.
tdelete() returns a pointer to the parent of the deleted node, or a null
pointer if the node is not found.

The twalk() function traverses a binary search tree. The root argument 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. The first argument is the address of the node being visited.
The second argument is a value from an enumeration data type

typedef enum { preorder, postorder, endorder, leaf } VISIT;

(defined in <search.h>), depending on whether this is the first, second
or third time that the node has been visited (during a depth-first, left-
to-right traversal of the tree), or whether the node is a leaf. The third
argument is the level of the node in the tree, with the root being level

The pointers to the key and the root of the tree should be of type
pointer-to-element, and cast to type pointer-to-character. Similarly,
although declared as type pointer-to-character, the value returned should
be cast into type pointer-to-element.


If the node is found, both tsearch() and tfind() return a pointer to it.
If not, tfind() returns a null pointer, and tsearch() returns a pointer
to the inserted item.

A null pointer is returned by tsearch() if there is not enough space
available to create a new node.

A null pointer is returned by tsearch(), tfind() and tdelete() if rootp
is a null pointer on entry.

The tdelete() function returns a pointer to the parent of the deleted
node, or a null pointer if the node is not found.

The twalk() function returns no value.


No errors are defined.


The root argument to twalk() is one level of indirection less than the
rootp arguments to tsearch() and tdelete().

There are two nomenclatures used to refer to the order in which tree
nodes are visited. tsearch() uses preorder, postorder and endorder to
refer respectively 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

If the calling function alters the pointer to the root, the results are

These functions safely allows concurrent access by multiple threads to
disjoint data, such as overlapping subtrees or tables.


Example 1: A sample program of using tsearch() function.

The following code reads in 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.

#include <string.h>
#include <stdio.h>
#include <search.h>
struct node {
char *string;
int length;
char string_space[10000];
struct node nodes[500];
void *root = NULL;

int node_compare(const void *node1, const void *node2) {
return strcmp(((const struct node *) node1)->string,
((const struct node *) node2)->string);

void print_node(const void *node, VISIT order, int level) {
if (order == preorder || order == leaf) {
printf("length=%d, string=%20s\n",
(*(struct node **)node)->length,
(*(struct node **)node)->string);

char *strptr = string_space;
struct node *nodeptr = nodes;
int i = 0;

while (gets(strptr) != NULL && i++ < 500) {
nodeptr->string = strptr;
nodeptr->length = strlen(strptr);
(void) tsearch((void *)nodeptr,
&root, node_compare);
strptr += nodeptr->length + 1;
twalk(root, print_node);


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | MT-Safe |


bsearch(3C), hsearch(3C), lsearch(3C), attributes(7), standards(7)

illumos December 6, 2004 TSEARCH(3C)