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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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. 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.
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 <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);
}
}
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.
None.
None.
hcreate(3p), lsearch(3p)
The Base Definitions volume of POSIX.1‐2017, search.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 TDELETE(3P)
Pages that refer to this page: search.h(0p), bsearch(3p), hcreate(3p), lsearch(3p), tfind(3p), tsearch(3p), twalk(3p)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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