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,
16 int (*compar)(const void *, const void *));
17 void *tdelete(const void *restrict key, void **restrict rootp,
18 int (*compar)(const void *, const void *));
19 void twalk(const void *root,
20 void (*action)(const void *nodep, VISIT which,
21 int depth));
22 #define _GNU_SOURCE /* See feature_test_macros(7) */
24 #include <search.h>
25 void twalk_r(const void *root,
27 void (*action)(const void *nodep, VISIT which,
28 void *closure),
29 void *closure);
30 void tdestroy(void *root, void (*free_node)(void *nodep));
31
33 tsearch(), tfind(), twalk(), and tdelete() manage a binary search tree.
34 They are generalized from Knuth (6.2.2) Algorithm T. The first field
35 in each node of the tree is a pointer to the corresponding data item.
36 (The calling program must store the actual data.) compar points to a
37 comparison routine, which takes pointers to two items. It should re‐
38 turn an integer which is negative, zero, or positive, depending on
39 whether the first item is less than, equal to, or greater than the sec‐
40 ond.
41 tsearch() searches the tree for an item. key points to the item to be
43 searched for. rootp points to a variable which points to the root of
44 the tree. If the tree is empty, then the variable that rootp points to
45 should be set to NULL. If the item is found in the tree, then
46 tsearch() returns a pointer to the corresponding tree node. (In other
47 words, tsearch() returns a pointer to a pointer to the data item.) If
48 the item is not found, then tsearch() adds it, and returns a pointer to
49 the corresponding tree node.
50 tfind() is like tsearch(), except that if the item is not found, then
52 tfind() returns NULL.
53 tdelete() deletes an item from the tree. Its arguments are the same as
55 for tsearch().
56 twalk() performs depth-first, left-to-right traversal of a binary tree.
58 root points to the starting node for the traversal. If that node is
59 not the root, then only part of the tree will be visited. twalk()
60 calls the user function action each time a node is visited (that is,
61 three times for an internal node, and once for a leaf). action, in
62 turn, takes three arguments. The first argument is a pointer to the
63 node being visited. The structure of the node is unspecified, but it
64 is possible to cast the pointer to a pointer-to-pointer-to-element in
65 order to access the element stored within the node. The application
66 must not modify the structure pointed to by this argument. The second
67 argument is an integer which takes one of the values preorder, pos‐
68 torder, or endorder depending on whether this is the first, second, or
69 third visit to the internal node, or the value leaf if this is the sin‐
70 gle visit to a leaf node. (These symbols are defined in <search.h>.)
71 The third argument is the depth of the node; the root node has depth
72 zero.
73 (More commonly, preorder, postorder, and endorder are known as pre‐
75 order, inorder, and postorder: before visiting the children, after the
76 first and before the second, and after visiting the children. Thus,
77 the choice of name postorder is rather confusing.)
78 twalk_r() is similar to twalk(), but instead of the depth argument, the
80 closure argument pointer is passed to each invocation of the action
81 callback, unchanged. This pointer can be used to pass information to
82 and from the callback function in a thread-safe fashion, without re‐
83 sorting to global variables.
84 tdestroy() removes the whole tree pointed to by root, freeing all re‐
86 sources allocated by the tsearch() function. For the data in each tree
87 node the function free_node is called. The pointer to the data is
88 passed as the argument to the function. If no such work is necessary,
89 free_node must point to a function doing nothing.
90
92 tsearch() returns a pointer to a matching node in the tree, or to the
93 newly added node, or NULL if there was insufficient memory to add the
94 item. tfind() returns a pointer to the node, or NULL if no match is
95 found. If there are multiple items that match the key, the item whose
96 node is returned is unspecified.
97 tdelete() returns a pointer to the parent of the node deleted, or NULL
99 if the item was not found. If the deleted node was the root node,
100 tdelete() returns a dangling pointer that must not be accessed.
101 tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL on
103 entry.
104
106 twalk_r() is available in glibc since version 2.30.
107
109 For an explanation of the terms used in this section, see at‐
110 tributes(7).
111 ┌─────────────────────────────────┬───────────────┬────────────────────┐
113 │Interface │ Attribute │ Value │
114 ├─────────────────────────────────┼───────────────┼────────────────────┤
115 │tsearch(), tfind(), tdelete() │ Thread safety │ MT-Safe race:rootp │
116 ├─────────────────────────────────┼───────────────┼────────────────────┤
117 │twalk() │ Thread safety │ MT-Safe race:root │
118 ├─────────────────────────────────┼───────────────┼────────────────────┤
119 │twalk_r() │ Thread safety │ MT-Safe race:root │
120 ├─────────────────────────────────┼───────────────┼────────────────────┤
121 │tdestroy() │ Thread safety │ MT-Safe │
122 └─────────────────────────────────┴───────────────┴────────────────────┘
123
125 POSIX.1-2001, POSIX.1-2008, SVr4. The functions tdestroy() and
126 twalk_r() are GNU extensions.
127
129 twalk() takes a pointer to the root, while the other functions take a
130 pointer to a variable which points to the root.
131 tdelete() frees the memory required for the node in the tree. The user
133 is responsible for freeing the memory for the corresponding data.
134 The example program depends on the fact that twalk() makes no further
136 reference to a node after calling the user function with argument "en‐
137 dorder" or "leaf". This works with the GNU library implementation, but
138 is not in the System V documentation.
139
141 The following program inserts twelve random numbers into a binary tree,
142 where duplicate numbers are collapsed, then prints the numbers in or‐
143 der.
144 #define _GNU_SOURCE /* Expose declaration of tdestroy() */
146 #include <search.h>
147 #include <stddef.h>
148 #include <stdlib.h>
149 #include <stdio.h>
150 #include <time.h>
151 static void *root = NULL;
153 static void *
155 xmalloc(size_t n)
156 {
157 void *p;
158 p = malloc(n);
159 if (p)
160 return p;
161 fprintf(stderr, "insufficient memory\n");
162 exit(EXIT_FAILURE);
163 }
164 static int
166 compare(const void *pa, const void *pb)
167 {
168 if (*(int *) pa < *(int *) pb)
169 return -1;
170 if (*(int *) pa > *(int *) pb)
171 return 1;
172 return 0;
173 }
174 static void
176 action(const void *nodep, VISIT which, int depth)
177 {
178 int *datap;
179 switch (which) {
181 case preorder:
182 break;
183 case postorder:
184 datap = *(int **) nodep;
185 printf("%6d\n", *datap);
186 break;
187 case endorder:
188 break;
189 case leaf:
190 datap = *(int **) nodep;
191 printf("%6d\n", *datap);
192 break;
193 }
194 }
195 int
197 main(void)
198 {
199 int **val;
200 srand(time(NULL));
202 for (int i = 0; i < 12; i++) {
203 int *ptr = xmalloc(sizeof(*ptr));
204 *ptr = rand() & 0xff;
205 val = tsearch(ptr, &root, compare);
206 if (val == NULL)
207 exit(EXIT_FAILURE);
208 else if (*val != ptr)
209 free(ptr);
210 }
211 twalk(root, action);
212 tdestroy(root, free);
213 exit(EXIT_SUCCESS);
214 }
215
217 bsearch(3), hsearch(3), lsearch(3), qsort(3)
218
220 This page is part of release 5.12 of the Linux man-pages project. A
221 description of the project, information about reporting bugs, and the
222 latest version of this page, can be found at
223 https://www.kernel.org/doc/man-pages/.
224GNU 2021-03-22 TSEARCH(3)