Originální popis anglicky:
tsearch, tfind, tdelete, twalk - manage a binary tree
Návod, kniha: Linux Programmer's Manual
#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));
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.
(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
rootp, 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.
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.
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 SysV documentation.
The following program inserts twelve random numbers into a binary tree, where
duplicate numbers are collapsed, then prints the numbers in order.
#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(1);
}
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() {
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(1);
}
twalk(root, action);
return 0;
}
SVID. The function
tdestroy() is a GNU extension.
bsearch(3),
hsearch(3),
lsearch(3),
qsort(3)
