| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
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, const void **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 is a
pointer to the node being visited. The second is an integer which takes on
the values preorder, postorder, and endorder depending on whether this is the
first, second, or third visit to the internal node, or leaf if it is the
single visit to a leaf node. (These symbols are defined in <search.h>.) The
third argument is the depth of the node, with zero being the root.
(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.
SVr4, POSIX.1-2001. 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.
twalk() uses postorder to mean "after the left subtree, but before the right
subtree". Some authorities would call this "inorder", and reserve "postorder"
to mean "after both subtrees".
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>
void *root = NULL;
void *
xmalloc(unsigned n)
{
void *p;
p = malloc(n);
if (p)
return p;
fprintf(stderr, "insufficient memory\n");
exit(EXIT_FAILURE);
}
int
compare(const void *pa, const void *pb)
{
if (*(int *) pa < *(int *) pb)
return -1;
if (*(int *) pa > *(int *) pb)
return 1;
return 0;
}
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 = (int *) 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 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
GNU 2008-09-23 TSEARCH(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface