Originální popis anglicky:
tdelete, tfind, tsearch, twalk - manage a binary search tree
Návod, kniha: POSIX Programmer's Manual
#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));
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.
The
tdelete() function shall return a pointer to the parent of the
deleted node, or a null pointer if the node is not found.
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 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 a null pointer if the node is not found.
The
twalk() function shall not return a value.
No errors are defined.
The following sections are informative.
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 <search.h>
#include <string.h>
#include <stdio.h>
#define STRSZ 10000
#define NODSZ 500
struct node { /* Pointers to these are stored in the tree. */
char *string;
int length;
};
char string_space[STRSZ]; /* Space to store strings. */
struct node nodes[NODSZ]; /* Nodes to store. */
void *root = NULL; /* This points to the root. */
int main(int argc, char *argv[])
{
char *strptr = string_space;
struct node *nodeptr = nodes;
void print_node(const void *, VISIT, int);
int i = 0, node_compare(const void *, const void *);
while (gets(strptr) != NULL && i++ < NODSZ) {
/* Set node. */
nodeptr->string = strptr;
nodeptr->length = strlen(strptr);
/* Put node into the tree. */
(void) tsearch((void *)nodeptr, (void **)&root,
node_compare);
/* Adjust pointers, so we do not overwrite tree. */
strptr += nodeptr->length + 1;
nodeptr++;
}
twalk(root, print_node);
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 node *) node1)->string,
((const struct node *) node2)->string);
}
/*
* 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 node *p = *(const struct node **) ptr;
if (order == postorder || order == leaf) {
(void) printf("string = %s, length = %d\n",
p->string, p->length);
}
}
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
tsearch() 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.
None.
None.
hcreate() ,
lsearch() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<search.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
