TSEARCH
Section: Linux Programmer's Manual (3)
Updated: 2015-08-08
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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.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
tsearch(),
tfind(),
tdelete()
| Thread safety | MT-Safe race:rootp
|
|
twalk()
| Thread safety | MT-Safe race:root
|
|
tdestroy()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4.
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
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- EXAMPLE
-
- SEE ALSO
-
- COLOPHON
-
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