NAME¶
tsearch, tfind, tdelete, twalk, tdestroy - manage a binary tree
SYNOPSIS¶
#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));
DESCRIPTION¶
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.
RETURN VALUE¶
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.
NOTES¶
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.
EXAMPLE¶
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);
}
SEE ALSO¶
bsearch(3),
hsearch(3),
lsearch(3),
qsort(3)
COLOPHON¶
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man-pages project. A
description of the project, information about reporting bugs, and the latest
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