tsearch(3) Library Functions Manual tsearch(3)
NAME
tsearch, tfind, tdelete, twalk, twalk_r, tdestroy - manage a binary
search tree
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <search.h>
typedef enum { preorder, postorder, endorder, leaf } VISIT;
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 *restrict key, void **restrict rootp,
int (*compar)(const void *, const void *));
void twalk(const void *root,
void (*action)(const void *nodep, VISIT which,
int depth));
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <search.h>
void twalk_r(const void *root,
void (*action)(const void *nodep, VISIT which,
void *closure),
void *closure);
void tdestroy(void *root, void (*free_node)(void *nodep));
DESCRIPTION
tsearch(), tfind(), twalk(), and tdelete() manage a binary search 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 re-
turn an integer which is negative, zero, or positive, depending on
whether the first item is less than, equal to, or greater than the sec-
ond.
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 the corresponding tree node. (In other
words, tsearch() returns a pointer to a pointer to the data item.) If
the item is not found, then tsearch() adds it, and returns a pointer to
the corresponding tree node.
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, pos-
torder, 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 sin-
gle 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 pre-
order, 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.)
twalk_r() is similar to twalk(), but instead of the depth argument, the
closure argument pointer is passed to each invocation of the action
callback, unchanged. This pointer can be used to pass information to
and from the callback function in a thread-safe fashion, without re-
sorting to global variables.
tdestroy() removes the whole tree pointed to by root, freeing all re-
sources 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 node in the tree, or to the
newly added node, or NULL if there was insufficient memory to add the
item. tfind() returns a pointer to the node, or NULL if no match is
found. If there are multiple items that match the key, the item whose
node is returned is unspecified.
tdelete() returns a pointer to the parent of the node deleted, or NULL
if the item was not found. If the deleted node was the root node,
tdelete() returns a dangling pointer that must not be accessed.
tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL on
entry.
VERSIONS
twalk_r() is available since glibc 2.30.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌─────────────────────────────────┬───────────────┬────────────────────┐
│Interface │ Attribute │ Value │
├─────────────────────────────────┼───────────────┼────────────────────┤
│tsearch(), tfind(), tdelete() │ Thread safety │ MT-Safe race:rootp │
├─────────────────────────────────┼───────────────┼────────────────────┤
│twalk() │ Thread safety │ MT-Safe race:root │
├─────────────────────────────────┼───────────────┼────────────────────┤
│twalk_r() │ Thread safety │ MT-Safe race:root │
├─────────────────────────────────┼───────────────┼────────────────────┤
│tdestroy() │ Thread safety │ MT-Safe │
└─────────────────────────────────┴───────────────┴────────────────────┘
STANDARDS
POSIX.1-2001, POSIX.1-2008, SVr4. The functions tdestroy() and
twalk_r() are GNU extensions.
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 "en-
dorder" or "leaf". This works with the GNU library implementation, but
is not in the System V documentation.
EXAMPLES
The following program inserts twelve random numbers into a binary tree,
where duplicate numbers are collapsed, then prints the numbers in or-
der.
#define _GNU_SOURCE /* Expose declaration of tdestroy() */
#include <search.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
static void *root = NULL;
static void *
xmalloc(size_t 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, VISIT which, 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 *ptr;
int **val;
srand(time(NULL));
for (unsigned int i = 0; i < 12; i++) {
ptr = xmalloc(sizeof(*ptr));
*ptr = rand() & 0xff;
val = tsearch(ptr, &root, compare);
if (val == NULL)
exit(EXIT_FAILURE);
if (*val != ptr)
free(ptr);
}
twalk(root, action);
tdestroy(root, free);
exit(EXIT_SUCCESS);
}
SEE ALSO
bsearch(3), hsearch(3), lsearch(3), qsort(3)
Linux man-pages 6.03 2023-01-26 tsearch(3)
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