TDELETE(3P) POSIX Programmer's Manual TDELETE(3P)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.
NAME
tdelete, tfind, tsearch, twalk — manage a binary search tree
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));
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 argu‐
ment 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 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 ele‐
ment 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, sec‐
ond, 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.
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.
ERRORS
No errors are defined.
The following sections are informative.
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 <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);
}
}
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 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 pos‐
torder to refer to the same visits, which could result in some confu‐
sion 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 implemen‐
tations 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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOhcreate(), lsearch()
The Base Definitions volume of POSIX.1‐2008, <search.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TDELETE(3P)
