управлять двоичным деревом поиска (manage a binary search tree)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
tdelete, tfind, tsearch, twalk — manage a binary search tree
Синопсис (Synopsis)
#include <search.h>
void *tdelete(const void *restrict key, void **restrict rootp,
int(*compar)(const void *, const void *));
void *tfind(const void *key, void *const *rootp,
int(*compar)(const void *, const void *));
void *tsearch(const void *key, void **rootp,
int (*compar)(const void *, const void *));
void twalk(const void *root,
void (*action)(const void *, VISIT, int));
Описание (Description)
The tdelete(), tfind(), tsearch(), and twalk() functions
manipulate binary search trees. Comparisons are made with a user-
supplied routine, the address of which is passed as the compar
argument. This routine is called with two arguments, which are
the pointers to the elements being compared. The application
shall ensure that the user-supplied routine returns an integer
less than, equal to, or greater than 0, according to whether the
first argument is to be considered less than, equal to, or
greater than the second argument. The comparison function need
not compare every byte, so arbitrary data may be contained in the
elements in addition to the values being compared.
The tsearch() function shall build and access the tree. The key
argument is a pointer to an element to be accessed or stored. If
there is a node in the tree whose element is equal to the value
pointed to by key, a pointer to this found node shall be
returned. Otherwise, the value pointed to by key shall be
inserted (that is, a new node is created and the value of key is
copied to this node), and a pointer to this node returned. Only
pointers are copied, so the application shall ensure that the
calling routine stores the data. The rootp argument points to a
variable that points to the root node of the tree. A null pointer
value for the variable pointed to by rootp denotes an empty tree;
in this case, the variable shall be set to point to the node
which shall be at the root of the new tree.
Like tsearch(), tfind() shall search for a node in the tree,
returning a pointer to it if found. However, if it is not found,
tfind() shall return a null pointer. The arguments for tfind()
are the same as for tsearch().
The tdelete() function shall delete a node from a binary search
tree. The arguments are the same as for tsearch(). The variable
pointed to by rootp shall be changed if the deleted node was the
root of the tree. If the deleted node was the root of the tree
and had no children, the variable pointed to by rootp shall be
set to a null pointer. The tdelete() function shall return a
pointer to the parent of the deleted node, or an unspecified non-
null pointer if the deleted node was the root node, or a null
pointer if the node is not found.
If tsearch() adds an element to a tree, or tdelete() successfully
deletes an element from a tree, the concurrent use of that tree
in another thread, or use of pointers produced by a previous call
to tfind() or tsearch(), produces undefined results.
The twalk() function shall traverse a binary search tree. The
root argument is a pointer to the root node of the tree to be
traversed. (Any node in a tree may be used as the root for a
walk below that node.) The argument action is the name of a
routine to be invoked at each node. This routine is, in turn,
called with three arguments. The first argument shall be the
address of the node being visited. The structure pointed to by
this argument is unspecified and shall not be modified by the
application, but it shall be possible to cast a pointer-to-node
into a pointer-to-pointer-to-element to access the element stored
in the node. The second argument shall be a value from an
enumeration data type:
typedef enum { preorder, postorder, endorder, leaf } VISIT;
(defined in <search.h>), depending on whether this is the first,
second, or third time that the node is visited (during a depth-
first, left-to-right traversal of the tree), or whether the node
is a leaf. The third argument shall be the level of the node in
the tree, with the root being level 0.
If the calling function alters the pointer to the root, the
result is undefined.
If the functions pointed to by action or compar (for any of these
binary search functions) change the tree, the results are
undefined.
These functions are thread-safe only as long as multiple threads
do not access the same tree.
Возвращаемое значение (Return value)
If the node is found, both tsearch() and tfind() shall return a
pointer to it. If not, tfind() shall return a null pointer, and
tsearch() shall return a pointer to the inserted item.
A null pointer shall be returned by tsearch() if there is not
enough space available to create a new node.
A null pointer shall be returned by tdelete(), tfind(), and
tsearch() if rootp is a null pointer on entry.
The tdelete() function shall return a pointer to the parent of
the deleted node, or an unspecified non-null pointer if the
deleted node was the root node, or a null pointer if the node is
not found.
The twalk() function shall not return a value.
Ошибки (Error)
No errors are defined.
The following sections are informative.
Примеры (Examples)
The following code reads in strings and stores structures
containing a pointer to each string and a count of its length. It
then walks the tree, printing out the stored strings and their
lengths in alphabetical order.
#include <limits.h>
#include <search.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
struct element { /* Pointers to these are stored in the tree. */
int count;
char string[];
};
void *root = NULL; /* This points to the root. */
int main(void)
{
char str[_POSIX2_LINE_MAX+1];
int length = 0;
struct element *elementptr;
void *node;
void print_node(const void *, VISIT, int);
int node_compare(const void *, const void *),
delete_root(const void *, const void *);
while (fgets(str, sizeof(str), stdin)) {
/* Set element. */
length = strlen(str);
if (str[length-1] == '\n')
str[--length] = '\0';
elementptr = malloc(sizeof(struct element) + length + 1);
strcpy(elementptr->string, str);
elementptr->count = 1;
/* Put element into the tree. */
node = tsearch((void *)elementptr, &root, node_compare);
if (node == NULL) {
fprintf(stderr,
"tsearch: Not enough space available\n");
exit(EXIT_FAILURE);
}
else if (*(struct element **)node != elementptr) {
/* A node containing the element already exists */
(*(struct element **)node)->count++;
free(elementptr);
}
}
twalk(root, print_node);
/* Delete all nodes in the tree */
while (root != NULL) {
elementptr = *(struct element **)root;
printf("deleting node: string = %s, count = %d\n",
elementptr->string,
elementptr->count);
tdelete((void *)elementptr, &root, delete_root);
free(elementptr);
}
return 0;
}
/*
* This routine compares two nodes, based on an
* alphabetical ordering of the string field.
*/
int
node_compare(const void *node1, const void *node2)
{
return strcmp(((const struct element *) node1)->string,
((const struct element *) node2)->string);
}
/*
* This comparison routine can be used with tdelete()
* when explicitly deleting a root node, as no comparison
* is necessary.
*/
int
delete_root(const void *node1, const void *node2)
{
return 0;
}
/*
* This routine prints out a node, the second time
* twalk encounters it or if it is a leaf.
*/
void
print_node(const void *ptr, VISIT order, int level)
{
const struct element *p = *(const struct element **) ptr;
if (order == postorder || order == leaf) {
(void) printf("string = %s, count = %d\n",
p->string, p->count);
}
}
Использование в приложениях (Application usage)
The root argument to twalk() is one level of indirection less
than the rootp arguments to tdelete() and tsearch().
There are two nomenclatures used to refer to the order in which
tree nodes are visited. The twalk() function uses preorder,
postorder, and endorder to refer respectively to visiting a node
before any of its children, after its left child and before its
right, and after both its children. The alternative nomenclature
uses preorder, inorder, and postorder to refer to the same
visits, which could result in some confusion over the meaning of
postorder.
Since the return value of tdelete() is an unspecified non-null
pointer in the case that the root of the tree has been deleted,
applications should only use the return value of tdelete() as
indication of success or failure and should not assume it can be
dereferenced. Some implementations in this case will return a
pointer to the new root of the tree (or to an empty tree if the
deleted root node was the only node in the tree); other
implementations return arbitrary non-null pointers.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
hcreate(3p), lsearch(3p)
The Base Definitions volume of POSIX.1‐2017, search.h(0p)
