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 compar-
ison 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 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 cor-
responding 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 vis-
ited. 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 inte-
ger which takes one of the values preorder, postorder, or endorder de-
pending on whether this is the first, second, or third visit to the in-
ternal 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.)
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 resort-
ing 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.
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 │
├─────────────────────────────────┼───────────────┼────────────────────┤
│ twalk_r() │ Thread safety │ MT-Safe race:root │
├─────────────────────────────────┼───────────────┼────────────────────┤
│ tdestroy() │ Thread safety │ MT-Safe │
└─────────────────────────────────┴───────────────┴────────────────────┘
STANDARDS
tsearch()
tfind()
tdelete()
twalk()
POSIX.1-2008.
tdestroy()
twalk_r()
GNU.
HISTORY
tsearch()
tfind()
tdelete()
twalk()
POSIX.1-2001, POSIX.1-2008, SVr4.
twalk_r()
glibc 2.30.
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 order.
#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)
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