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, 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
#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 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. You
should not modify the tree while traversing it as the the results would
be undefined.
(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.
CONFORMING TO
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.
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.
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>
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);
}
SEE ALSO
bsearch(3), hsearch(3), lsearch(3), qsort(3), feature_test_macros(7)
COLOPHON
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