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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
TSEARCH(3) Linux Programmer's Manual TSEARCH(3)
tsearch, tfind, tdelete, twalk, tdestroy - manage a binary tree
#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 *key, void **rootp,
int (*compar)(const void *, const void *));
void twalk(const void *root, void (*action)(const void *nodep,
const VISIT which,
const int depth));
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <search.h>
void tdestroy(void *root, void (*free_node)(void *nodep));
tsearch(), tfind(), twalk(), and tdelete() manage a binary tree.
They are generalized from Knuth (6.2.2) Algorithm T. The first field
in each node of the tree is a pointer to the corresponding data item.
(The calling program must store the actual data.) compar points to a
comparison routine, which takes pointers to two items. It should
return an integer which is negative, zero, or positive, depending on
whether the first item is less than, equal to, or greater than the
second.
tsearch() searches the tree for an item. key points to the item to
be searched for. rootp points to a variable which points to the root
of the tree. If the tree is empty, then the variable that rootp
points to should be set to NULL. If the item is found in the tree,
then tsearch() returns a pointer to it. If it is not found, then
tsearch() adds it, and returns a pointer to the newly added item.
tfind() is like tsearch(), except that if the item is not found, then
tfind() returns NULL.
tdelete() deletes an item from the tree. Its arguments are the same
as for tsearch().
twalk() performs depth-first, left-to-right traversal of a binary
tree. root points to the starting node for the traversal. If that
node is not the root, then only part of the tree will be visited.
twalk() calls the user function action each time a node is visited
(that is, three times for an internal node, and once for a leaf).
action, in turn, takes three arguments. The first argument is a
pointer to the node being visited. The structure of the node is
unspecified, but it is possible to cast the pointer to a pointer-to-
pointer-to-element in order to access the element stored within the
node. The application must not modify the structure pointed to by
this argument. The second argument is an integer which takes one of
the values preorder, postorder, or endorder depending on whether this
is the first, second, or third visit to the internal node, or the
value leaf if this is the single visit to a leaf node. (These
symbols are defined in <search.h>.) The third argument is the depth
of the node; the root node has depth zero.
(More commonly, preorder, postorder, and endorder are known as
preorder, inorder, and postorder: before visiting the children, after
the first and before the second, and after visiting the children.
Thus, the choice of name postorder is rather confusing.)
tdestroy() removes the whole tree pointed to by root, freeing all
resources allocated by the tsearch() function. For the data in each
tree node the function free_node is called. The pointer to the data
is passed as the argument to the function. If no such work is
necessary, free_node must point to a function doing nothing.
tsearch() returns a pointer to a matching item in the tree, or to the
newly added item, or NULL if there was insufficient memory to add the
item. tfind() returns a pointer to the item, or NULL if no match is
found. If there are multiple elements that match the key, the
element returned is unspecified.
tdelete() returns a pointer to the parent of the item deleted, or
NULL if the item was not found.
tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL
on entry.
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────┬───────────────┬────────────────────┐
│Interface │ Attribute │ Value │
├────────────────────┼───────────────┼────────────────────┤
│tsearch(), tfind(), │ Thread safety │ MT-Safe race:rootp │
│tdelete() │ │ │
├────────────────────┼───────────────┼────────────────────┤
│twalk() │ Thread safety │ MT-Safe race:root │
├────────────────────┼───────────────┼────────────────────┤
│tdestroy() │ Thread safety │ MT-Safe │
└────────────────────┴───────────────┴────────────────────┘
POSIX.1-2001, POSIX.1-2008, SVr4. The function tdestroy() is a GNU
extension.
twalk() takes a pointer to the root, while the other functions take a
pointer to a variable which points to the root.
tdelete() frees the memory required for the node in the tree. The
user is responsible for freeing the memory for the corresponding
data.
The example program depends on the fact that twalk() makes no further
reference to a node after calling the user function with argument
"endorder" or "leaf". This works with the GNU library
implementation, but is not in the System V documentation.
The following program inserts twelve random numbers into a binary
tree, where duplicate numbers are collapsed, then prints the numbers
in order.
#define _GNU_SOURCE /* Expose declaration of tdestroy() */
#include <search.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
static void *root = NULL;
static void *
xmalloc(unsigned n)
{
void *p;
p = malloc(n);
if (p)
return p;
fprintf(stderr, "insufficient memory\n");
exit(EXIT_FAILURE);
}
static int
compare(const void *pa, const void *pb)
{
if (*(int *) pa < *(int *) pb)
return -1;
if (*(int *) pa > *(int *) pb)
return 1;
return 0;
}
static void
action(const void *nodep, const VISIT which, const int depth)
{
int *datap;
switch (which) {
case preorder:
break;
case postorder:
datap = *(int **) nodep;
printf("%6d\n", *datap);
break;
case endorder:
break;
case leaf:
datap = *(int **) nodep;
printf("%6d\n", *datap);
break;
}
}
int
main(void)
{
int i, *ptr;
void *val;
srand(time(NULL));
for (i = 0; i < 12; i++) {
ptr = xmalloc(sizeof(int));
*ptr = rand() & 0xff;
val = tsearch((void *) ptr, &root, compare);
if (val == NULL)
exit(EXIT_FAILURE);
else if ((*(int **) val) != ptr)
free(ptr);
}
twalk(root, action);
tdestroy(root, free);
exit(EXIT_SUCCESS);
}
bsearch(3), hsearch(3), lsearch(3), qsort(3)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2015-08-08 TSEARCH(3)
Pages that refer to this page: bsearch(3), hsearch(3), lsearch(3)