1tsearch(3) Library Functions Manual tsearch(3)
2
6 tsearch, tfind, tdelete, twalk, twalk_r, tdestroy - manage a binary
7 search tree
8
10 Standard C library (libc, -lc)
11
13 #include <search.h>
14 typedef enum { preorder, postorder, endorder, leaf } VISIT;
16 void *tsearch(const void *key, void **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 *tdelete(const void *restrict key, void **restrict rootp,
22 int (*compar)(const void *, const void *));
23 void twalk(const void *root,
24 void (*action)(const void *nodep, VISIT which,
25 int depth));
26 #define _GNU_SOURCE /* See feature_test_macros(7) */
28 #include <search.h>
29 void twalk_r(const void *root,
31 void (*action)(const void *nodep, VISIT which,
32 void *closure),
33 void *closure);
34 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 For an explanation of the terms used in this section, see at‐
111 tributes(7).
112 ┌─────────────────────────────────┬───────────────┬────────────────────┐
114 │Interface │ Attribute │ Value │
115 ├─────────────────────────────────┼───────────────┼────────────────────┤
116 │tsearch(), tfind(), tdelete() │ Thread safety │ MT-Safe race:rootp │
117 ├─────────────────────────────────┼───────────────┼────────────────────┤
118 │twalk() │ Thread safety │ MT-Safe race:root │
119 ├─────────────────────────────────┼───────────────┼────────────────────┤
120 │twalk_r() │ Thread safety │ MT-Safe race:root │
121 ├─────────────────────────────────┼───────────────┼────────────────────┤
122 │tdestroy() │ Thread safety │ MT-Safe │
123 └─────────────────────────────────┴───────────────┴────────────────────┘
124
126 tsearch()
127 tfind()
128 tdelete()
129 twalk()
130 POSIX.1-2008.
131 tdestroy()
133 twalk_r()
134 GNU.
135
137 tsearch()
138 tfind()
139 tdelete()
140 twalk()
141 POSIX.1-2001, POSIX.1-2008, SVr4.
142 twalk_r()
144 glibc 2.30.
145
147 twalk() takes a pointer to the root, while the other functions take a
148 pointer to a variable which points to the root.
149 tdelete() frees the memory required for the node in the tree. The user
151 is responsible for freeing the memory for the corresponding data.
152 The example program depends on the fact that twalk() makes no further
154 reference to a node after calling the user function with argument
155 "endorder" or "leaf". This works with the GNU library implementation,
156 but is not in the System V documentation.
157
159 The following program inserts twelve random numbers into a binary tree,
160 where duplicate numbers are collapsed, then prints the numbers in
161 order.
162 #define _GNU_SOURCE /* Expose declaration of tdestroy() */
164 #include <search.h>
165 #include <stddef.h>
166 #include <stdio.h>
167 #include <stdlib.h>
168 #include <time.h>
169 static void *root = NULL;
171 static void *
173 xmalloc(size_t n)
174 {
175 void *p;
176 p = malloc(n);
178 if (p)
179 return p;
180 fprintf(stderr, "insufficient memory\n");
181 exit(EXIT_FAILURE);
182 }
183 static int
185 compare(const void *pa, const void *pb)
186 {
187 if (*(int *) pa < *(int *) pb)
188 return -1;
189 if (*(int *) pa > *(int *) pb)
190 return 1;
191 return 0;
192 }
193 static void
195 action(const void *nodep, VISIT which, int depth)
196 {
197 int *datap;
198 switch (which) {
200 case preorder:
201 break;
202 case postorder:
203 datap = *(int **) nodep;
204 printf("%6d\n", *datap);
205 break;
206 case endorder:
207 break;
208 case leaf:
209 datap = *(int **) nodep;
210 printf("%6d\n", *datap);
211 break;
212 }
213 }
214 int
216 main(void)
217 {
218 int *ptr;
219 int **val;
220 srand(time(NULL));
222 for (unsigned int i = 0; i < 12; i++) {
223 ptr = xmalloc(sizeof(*ptr));
224 *ptr = rand() & 0xff;
225 val = tsearch(ptr, &root, compare);
226 if (val == NULL)
227 exit(EXIT_FAILURE);
228 if (*val != ptr)
229 free(ptr);
230 }
231 twalk(root, action);
232 tdestroy(root, free);
233 exit(EXIT_SUCCESS);
234 }
235
237 bsearch(3), hsearch(3), lsearch(3), qsort(3)
238Linux man-pages 6.05 2023-07-20 tsearch(3)