1TSEARCH(3) Linux Programmer's Manual TSEARCH(3)
2
6 tsearch, tfind, tdelete, twalk, tdestroy - manage a binary search tree
7
9 #include <search.h>
10 typedef enum { preorder, postorder, endorder, leaf } VISIT;
12 void *tsearch(const void *key, void **rootp,
14 int (*compar)(const void *, const void *));
15 void *tfind(const void *key, void *const *rootp,
17 int (*compar)(const void *, const void *));
18 void *tdelete(const void *key, void **rootp,
20 int (*compar)(const void *, const void *));
21 void twalk(const void *root,
23 void (*action)(const void *nodep, VISIT which,
24 int depth));
25 #define _GNU_SOURCE /* See feature_test_macros(7) */
27 #include <search.h>
28 void twalk_r(const void *root,
30 void (*action)(const void *nodep, VISIT which,
31 void *closure),
32 void *closure);
33 void tdestroy(void *root, void (*free_node)(void *nodep));
35
37 tsearch(), tfind(), twalk(), and tdelete() manage a binary search tree.
38 They are generalized from Knuth (6.2.2) Algorithm T. The first field
39 in each node of the tree is a pointer to the corresponding data item.
40 (The calling program must store the actual data.) compar points to a
41 comparison routine, which takes pointers to two items. It should re‐
42 turn an integer which is negative, zero, or positive, depending on
43 whether the first item is less than, equal to, or greater than the sec‐
44 ond.
45 tsearch() searches the tree for an item. key points to the item to be
47 searched for. rootp points to a variable which points to the root of
48 the tree. If the tree is empty, then the variable that rootp points to
49 should be set to NULL. If the item is found in the tree, then
50 tsearch() returns a pointer to the corresponding tree node. (In other
51 words, tsearch() returns a pointer to a pointer to the data item.) If
52 the item is not found, then tsearch() adds it, and returns a pointer to
53 the corresponding tree node.
54 tfind() is like tsearch(), except that if the item is not found, then
56 tfind() returns NULL.
57 tdelete() deletes an item from the tree. Its arguments are the same as
59 for tsearch().
60 twalk() performs depth-first, left-to-right traversal of a binary tree.
62 root points to the starting node for the traversal. If that node is
63 not the root, then only part of the tree will be visited. twalk()
64 calls the user function action each time a node is visited (that is,
65 three times for an internal node, and once for a leaf). action, in
66 turn, takes three arguments. The first argument is a pointer to the
67 node being visited. The structure of the node is unspecified, but it
68 is possible to cast the pointer to a pointer-to-pointer-to-element in
69 order to access the element stored within the node. The application
70 must not modify the structure pointed to by this argument. The second
71 argument is an integer which takes one of the values preorder, pos‐
72 torder, or endorder depending on whether this is the first, second, or
73 third visit to the internal node, or the value leaf if this is the sin‐
74 gle visit to a leaf node. (These symbols are defined in <search.h>.)
75 The third argument is the depth of the node; the root node has depth
76 zero.
77 (More commonly, preorder, postorder, and endorder are known as pre‐
79 order, inorder, and postorder: before visiting the children, after the
80 first and before the second, and after visiting the children. Thus,
81 the choice of name postorder is rather confusing.)
82 twalk_r() is similar to twalk(), but instead of the depth argument, the
84 closure argument pointer is passed to each invocation of the action
85 callback, unchanged. This pointer can be used to pass information to
86 and from the callback function in a thread-safe fashion, without re‐
87 sorting to global variables.
88 tdestroy() removes the whole tree pointed to by root, freeing all re‐
90 sources allocated by the tsearch() function. For the data in each tree
91 node the function free_node is called. The pointer to the data is
92 passed as the argument to the function. If no such work is necessary,
93 free_node must point to a function doing nothing.
94
96 tsearch() returns a pointer to a matching node in the tree, or to the
97 newly added node, or NULL if there was insufficient memory to add the
98 item. tfind() returns a pointer to the node, or NULL if no match is
99 found. If there are multiple items that match the key, the item whose
100 node is returned is unspecified.
101 tdelete() returns a pointer to the parent of the node deleted, or NULL
103 if the item was not found. If the deleted node was the root node,
104 tdelete() returns a dangling pointer that must not be accessed.
105 tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL on
107 entry.
108
110 twalk_r() is available in glibc since version 2.30.
111
113 For an explanation of the terms used in this section, see at‐
114 tributes(7).
115 ┌────────────────────┬───────────────┬────────────────────┐
117 │Interface │ Attribute │ Value │
118 ├────────────────────┼───────────────┼────────────────────┤
119 │tsearch(), tfind(), │ Thread safety │ MT-Safe race:rootp │
120 │tdelete() │ │ │
121 ├────────────────────┼───────────────┼────────────────────┤
122 │twalk() │ Thread safety │ MT-Safe race:root │
123 ├────────────────────┼───────────────┼────────────────────┤
124 │twalk_r() │ Thread safety │ MT-Safe race:root │
125 ├────────────────────┼───────────────┼────────────────────┤
126 │tdestroy() │ Thread safety │ MT-Safe │
127 └────────────────────┴───────────────┴────────────────────┘
129 POSIX.1-2001, POSIX.1-2008, SVr4. The functions tdestroy() and
130 twalk_r() are GNU extensions.
131
133 twalk() takes a pointer to the root, while the other functions take a
134 pointer to a variable which points to the root.
135 tdelete() frees the memory required for the node in the tree. The user
137 is responsible for freeing the memory for the corresponding data.
138 The example program depends on the fact that twalk() makes no further
140 reference to a node after calling the user function with argument "en‐
141 dorder" or "leaf". This works with the GNU library implementation, but
142 is not in the System V documentation.
143
145 The following program inserts twelve random numbers into a binary tree,
146 where duplicate numbers are collapsed, then prints the numbers in or‐
147 der.
148 #define _GNU_SOURCE /* Expose declaration of tdestroy() */
150 #include <search.h>
151 #include <stddef.h>
152 #include <stdlib.h>
153 #include <stdio.h>
154 #include <time.h>
155 static void *root = NULL;
157 static void *
159 xmalloc(size_t n)
160 {
161 void *p;
162 p = malloc(n);
163 if (p)
164 return p;
165 fprintf(stderr, "insufficient memory\n");
166 exit(EXIT_FAILURE);
167 }
168 static int
170 compare(const void *pa, const void *pb)
171 {
172 if (*(int *) pa < *(int *) pb)
173 return -1;
174 if (*(int *) pa > *(int *) pb)
175 return 1;
176 return 0;
177 }
178 static void
180 action(const void *nodep, VISIT which, int depth)
181 {
182 int *datap;
183 switch (which) {
185 case preorder:
186 break;
187 case postorder:
188 datap = *(int **) nodep;
189 printf("%6d\n", *datap);
190 break;
191 case endorder:
192 break;
193 case leaf:
194 datap = *(int **) nodep;
195 printf("%6d\n", *datap);
196 break;
197 }
198 }
199 int
201 main(void)
202 {
203 int **val;
204 srand(time(NULL));
206 for (int i = 0; i < 12; i++) {
207 int *ptr = xmalloc(sizeof(*ptr));
208 *ptr = rand() & 0xff;
209 val = tsearch(ptr, &root, compare);
210 if (val == NULL)
211 exit(EXIT_FAILURE);
212 else if (*val != ptr)
213 free(ptr);
214 }
215 twalk(root, action);
216 tdestroy(root, free);
217 exit(EXIT_SUCCESS);
218 }
219
221 bsearch(3), hsearch(3), lsearch(3), qsort(3)
222
224 This page is part of release 5.10 of the Linux man-pages project. A
225 description of the project, information about reporting bugs, and the
226 latest version of this page, can be found at
227 https://www.kernel.org/doc/man-pages/.
228GNU 2020-11-01 TSEARCH(3)