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TDELETE(3P) POSIX Programmer's Manual TDELETE(3P)
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.
tdelete, tfind, tsearch, twalk — manage a binary search tree
#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 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.
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.
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.
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.
None.
None.
hcreate(3p), lsearch(3p)
The Base Definitions volume of POSIX.1‐2008, search.h(0p)
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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TDELETE(3P)
Pages that refer to this page: search.h(0p), bsearch(3p), hcreate(3p), lsearch(3p), tfind(3p), tsearch(3p), twalk(3p)