1TDELETE(3P) POSIX Programmer's Manual TDELETE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 tdelete, tfind, tsearch, twalk — manage a binary search tree
13
15 #include <search.h>
16 void *tdelete(const void *restrict key, void **restrict rootp,
18 int(*compar)(const void *, const void *));
19 void *tfind(const void *key, void *const *rootp,
20 int(*compar)(const void *, const void *));
21 void *tsearch(const void *key, void **rootp,
22 int (*compar)(const void *, const void *));
23 void twalk(const void *root,
24 void (*action)(const void *, VISIT, int));
25
27 The tdelete(), tfind(), tsearch(), and twalk() functions manipulate
28 binary search trees. Comparisons are made with a user-supplied routine,
29 the address of which is passed as the compar argument. This routine is
30 called with two arguments, which are the pointers to the elements being
31 compared. The application shall ensure that the user-supplied routine
32 returns an integer less than, equal to, or greater than 0, according to
33 whether the first argument is to be considered less than, equal to, or
34 greater than the second argument. The comparison function need not
35 compare every byte, so arbitrary data may be contained in the elements
36 in addition to the values being compared.
37 The tsearch() function shall build and access the tree. The key argu‐
39 ment is a pointer to an element to be accessed or stored. If there is a
40 node in the tree whose element is equal to the value pointed to by key,
41 a pointer to this found node shall be returned. Otherwise, the value
42 pointed to by key shall be inserted (that is, a new node is created and
43 the value of key is copied to this node), and a pointer to this node
44 returned. Only pointers are copied, so the application shall ensure
45 that the calling routine stores the data. The rootp argument points to
46 a variable that points to the root node of the tree. A null pointer
47 value for the variable pointed to by rootp denotes an empty tree; in
48 this case, the variable shall be set to point to the node which shall
49 be at the root of the new tree.
50 Like tsearch(), tfind() shall search for a node in the tree, returning
52 a pointer to it if found. However, if it is not found, tfind() shall
53 return a null pointer. The arguments for tfind() are the same as for
54 tsearch().
55 The tdelete() function shall delete a node from a binary search tree.
57 The arguments are the same as for tsearch(). The variable pointed to
58 by rootp shall be changed if the deleted node was the root of the tree.
59 If the deleted node was the root of the tree and had no children, the
60 variable pointed to by rootp shall be set to a null pointer. The
61 tdelete() function shall return a pointer to the parent of the deleted
62 node, or an unspecified non-null pointer if the deleted node was the
63 root node, or a null pointer if the node is not found.
64 If tsearch() adds an element to a tree, or tdelete() successfully
66 deletes an element from a tree, the concurrent use of that tree in
67 another thread, or use of pointers produced by a previous call to
68 tfind() or tsearch(), produces undefined results.
69 The twalk() function shall traverse a binary search tree. The root
71 argument is a pointer to the root node of the tree to be traversed.
72 (Any node in a tree may be used as the root for a walk below that
73 node.) The argument action is the name of a routine to be invoked at
74 each node. This routine is, in turn, called with three arguments. The
75 first argument shall be the address of the node being visited. The
76 structure pointed to by this argument is unspecified and shall not be
77 modified by the application, but it shall be possible to cast a
78 pointer-to-node into a pointer-to-pointer-to-element to access the ele‐
79 ment stored in the node. The second argument shall be a value from an
80 enumeration data type:
81 typedef enum { preorder, postorder, endorder, leaf } VISIT;
84 (defined in <search.h>), depending on whether this is the first, sec‐
86 ond, or third time that the node is visited (during a depth-first,
87 left-to-right traversal of the tree), or whether the node is a leaf.
88 The third argument shall be the level of the node in the tree, with the
89 root being level 0.
90 If the calling function alters the pointer to the root, the result is
92 undefined.
93 If the functions pointed to by action or compar (for any of these
95 binary search functions) change the tree, the results are undefined.
96 These functions are thread-safe only as long as multiple threads do not
98 access the same tree.
99
101 If the node is found, both tsearch() and tfind() shall return a pointer
102 to it. If not, tfind() shall return a null pointer, and tsearch() shall
103 return a pointer to the inserted item.
104 A null pointer shall be returned by tsearch() if there is not enough
106 space available to create a new node.
107 A null pointer shall be returned by tdelete(), tfind(), and tsearch()
109 if rootp is a null pointer on entry.
110 The tdelete() function shall return a pointer to the parent of the
112 deleted node, or an unspecified non-null pointer if the deleted node
113 was the root node, or a null pointer if the node is not found.
114 The twalk() function shall not return a value.
116
118 No errors are defined.
119 The following sections are informative.
121
123 The following code reads in strings and stores structures containing a
124 pointer to each string and a count of its length. It then walks the
125 tree, printing out the stored strings and their lengths in alphabetical
126 order.
127 #include <limits.h>
130 #include <search.h>
131 #include <stdlib.h>
132 #include <string.h>
133 #include <stdio.h>
134 struct element { /* Pointers to these are stored in the tree. */
136 int count;
137 char string[];
138 };
139 void *root = NULL; /* This points to the root. */
141 int main(void)
143 {
144 char str[_POSIX2_LINE_MAX+1];
145 int length = 0;
146 struct element *elementptr;
147 void *node;
148 void print_node(const void *, VISIT, int);
149 int node_compare(const void *, const void *),
150 delete_root(const void *, const void *);
151 while (fgets(str, sizeof(str), stdin)) {
153 /* Set element. */
154 length = strlen(str);
155 if (str[length-1] == '\n')
156 str[--length] = '\0';
157 elementptr = malloc(sizeof(struct element) + length + 1);
158 strcpy(elementptr->string, str);
159 elementptr->count = 1;
160 /* Put element into the tree. */
161 node = tsearch((void *)elementptr, &root, node_compare);
162 if (node == NULL) {
163 fprintf(stderr,
164 "tsearch: Not enough space available\n");
165 exit(EXIT_FAILURE);
166 }
167 else if (*(struct element **)node != elementptr) {
168 /* A node containing the element already exists */
169 (*(struct element **)node)->count++;
170 free(elementptr);
171 }
172 }
173 twalk(root, print_node);
174 /* Delete all nodes in the tree */
176 while (root != NULL) {
177 elementptr = *(struct element **)root;
178 printf("deleting node: string = %s, count = %d\n",
179 elementptr->string,
180 elementptr->count);
181 tdelete((void *)elementptr, &root, delete_root);
182 free(elementptr);
183 }
184 return 0;
186 }
187 /*
189 * This routine compares two nodes, based on an
190 * alphabetical ordering of the string field.
191 */
192 int
193 node_compare(const void *node1, const void *node2)
194 {
195 return strcmp(((const struct element *) node1)->string,
196 ((const struct element *) node2)->string);
197 }
198 /*
200 * This comparison routine can be used with tdelete()
201 * when explicitly deleting a root node, as no comparison
202 * is necessary.
203 */
204 int
205 delete_root(const void *node1, const void *node2)
206 {
207 return 0;
208 }
209 /*
211 * This routine prints out a node, the second time
212 * twalk encounters it or if it is a leaf.
213 */
214 void
215 print_node(const void *ptr, VISIT order, int level)
216 {
217 const struct element *p = *(const struct element **) ptr;
218 if (order == postorder || order == leaf) {
220 (void) printf("string = %s, count = %d\n",
221 p->string, p->count);
222 }
223 }
224
226 The root argument to twalk() is one level of indirection less than the
227 rootp arguments to tdelete() and tsearch().
228 There are two nomenclatures used to refer to the order in which tree
230 nodes are visited. The twalk() function uses preorder, postorder, and
231 endorder to refer respectively to visiting a node before any of its
232 children, after its left child and before its right, and after both its
233 children. The alternative nomenclature uses preorder, inorder, and pos‐
234 torder to refer to the same visits, which could result in some confu‐
235 sion over the meaning of postorder.
236 Since the return value of tdelete() is an unspecified non-null pointer
238 in the case that the root of the tree has been deleted, applications
239 should only use the return value of tdelete() as indication of success
240 or failure and should not assume it can be dereferenced. Some implemen‐
241 tations in this case will return a pointer to the new root of the tree
242 (or to an empty tree if the deleted root node was the only node in the
243 tree); other implementations return arbitrary non-null pointers.
244
246 None.
247
249 None.
250
252 hcreate(), lsearch()
253 The Base Definitions volume of POSIX.1‐2017, <search.h>
255
257 Portions of this text are reprinted and reproduced in electronic form
258 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
259 table Operating System Interface (POSIX), The Open Group Base Specifi‐
260 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
261 Electrical and Electronics Engineers, Inc and The Open Group. In the
262 event of any discrepancy between this version and the original IEEE and
263 The Open Group Standard, the original IEEE and The Open Group Standard
264 is the referee document. The original Standard can be obtained online
265 at http://www.opengroup.org/unix/online.html .
266 Any typographical or formatting errors that appear in this page are
268 most likely to have been introduced during the conversion of the source
269 files to man page format. To report such errors, see https://www.ker‐
270 nel.org/doc/man-pages/reporting_bugs.html .
271IEEE/The Open Group 2017 TDELETE(3P)