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
42 return 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
87 resorting to global variables.
88 tdestroy() removes the whole tree pointed to by root, freeing all
90 resources allocated by the tsearch() function. For the data in each
91 tree 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
114 attributes(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
141 "endorder" or "leaf". This works with the GNU library implementation,
142 but 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
147 order.
148 #define _GNU_SOURCE /* Expose declaration of tdestroy() */
150 #include <search.h>
151 #include <stdlib.h>
152 #include <stdio.h>
153 #include <time.h>
154 static void *root = NULL;
156 static void *
158 xmalloc(unsigned n)
159 {
160 void *p;
161 p = malloc(n);
162 if (p)
163 return p;
164 fprintf(stderr, "insufficient memory\n");
165 exit(EXIT_FAILURE);
166 }
167 static int
169 compare(const void *pa, const void *pb)
170 {
171 if (*(int *) pa < *(int *) pb)
172 return -1;
173 if (*(int *) pa > *(int *) pb)
174 return 1;
175 return 0;
176 }
177 static void
179 action(const void *nodep, VISIT which, int depth)
180 {
181 int *datap;
182 switch (which) {
184 case preorder:
185 break;
186 case postorder:
187 datap = *(int **) nodep;
188 printf("%6d\n", *datap);
189 break;
190 case endorder:
191 break;
192 case leaf:
193 datap = *(int **) nodep;
194 printf("%6d\n", *datap);
195 break;
196 }
197 }
198 int
200 main(void)
201 {
202 int i, *ptr;
203 void *val;
204 srand(time(NULL));
206 for (i = 0; i < 12; i++) {
207 ptr = xmalloc(sizeof(int));
208 *ptr = rand() & 0xff;
209 val = tsearch((void *) ptr, &root, compare);
210 if (val == NULL)
211 exit(EXIT_FAILURE);
212 else if ((*(int **) 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 5.02 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 2019-05-09 TSEARCH(3)