1TSEARCH(3) Linux Programmer's Manual TSEARCH(3)
2
6 tsearch, tfind, tdelete, twalk, tdestroy - manage a binary tree
7
9 #include <search.h>
10 void *tsearch(const void *key, void **rootp,
12 int (*compar)(const void *, const void *));
13 void *tfind(const void *key, void *const *rootp,
15 int (*compar)(const void *, const void *));
16 void *tdelete(const void *key, void **rootp,
18 int (*compar)(const void *, const void *));
19 void twalk(const void *root, void (*action)(const void *nodep,
21 const VISIT which,
22 const int depth));
23 #define _GNU_SOURCE /* See feature_test_macros(7) */
25 #include <search.h>
26 void tdestroy(void *root, void (*free_node)(void *nodep));
28
30 tsearch(), tfind(), twalk(), and tdelete() manage a binary tree. They
31 are generalized from Knuth (6.2.2) Algorithm T. The first field in
32 each node of the tree is a pointer to the corresponding data item.
33 (The calling program must store the actual data.) compar points to a
34 comparison routine, which takes pointers to two items. It should
35 return an integer which is negative, zero, or positive, depending on
36 whether the first item is less than, equal to, or greater than the sec‐
37 ond.
38 tsearch() searches the tree for an item. key points to the item to be
40 searched for. rootp points to a variable which points to the root of
41 the tree. If the tree is empty, then the variable that rootp points to
42 should be set to NULL. If the item is found in the tree, then
43 tsearch() returns a pointer to it. If it is not found, then tsearch()
44 adds it, and returns a pointer to the newly added item.
45 tfind() is like tsearch(), except that if the item is not found, then
47 tfind() returns NULL.
48 tdelete() deletes an item from the tree. Its arguments are the same as
50 for tsearch().
51 twalk() performs depth-first, left-to-right traversal of a binary tree.
53 root points to the starting node for the traversal. If that node is
54 not the root, then only part of the tree will be visited. twalk()
55 calls the user function action each time a node is visited (that is,
56 three times for an internal node, and once for a leaf). action, in
57 turn, takes three arguments. The first argument is a pointer to the
58 node being visited. The structure of the node is unspecified, but it
59 is possible to cast the pointer to a pointer-to-pointer-to-element in
60 order to access the element stored within the node. The application
61 must not modify the structure pointed to by this argument. The second
62 argument is an integer which takes one of the values preorder, pos‐
63 torder, or endorder depending on whether this is the first, second, or
64 third visit to the internal node, or the value leaf if this is the sin‐
65 gle visit to a leaf node. (These symbols are defined in <search.h>.)
66 The third argument is the depth of the node; the root node has depth
67 zero.
68 (More commonly, preorder, postorder, and endorder are known as pre‐
70 order, inorder, and postorder: before visiting the children, after the
71 first and before the second, and after visiting the children. Thus,
72 the choice of name postorder is rather confusing.)
73 tdestroy() removes the whole tree pointed to by root, freeing all
75 resources allocated by the tsearch() function. For the data in each
76 tree node the function free_node is called. The pointer to the data is
77 passed as the argument to the function. If no such work is necessary,
78 free_node must point to a function doing nothing.
79
81 tsearch() returns a pointer to a matching item in the tree, or to the
82 newly added item, or NULL if there was insufficient memory to add the
83 item. tfind() returns a pointer to the item, or NULL if no match is
84 found. If there are multiple elements that match the key, the element
85 returned is unspecified.
86 tdelete() returns a pointer to the parent of the item deleted, or NULL
88 if the item was not found.
89 tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL on
91 entry.
92
94 For an explanation of the terms used in this section, see
95 attributes(7).
96 ┌────────────────────┬───────────────┬────────────────────┐
98 │Interface │ Attribute │ Value │
99 ├────────────────────┼───────────────┼────────────────────┤
100 │tsearch(), tfind(), │ Thread safety │ MT-Safe race:rootp │
101 │tdelete() │ │ │
102 ├────────────────────┼───────────────┼────────────────────┤
103 │twalk() │ Thread safety │ MT-Safe race:root │
104 ├────────────────────┼───────────────┼────────────────────┤
105 │tdestroy() │ Thread safety │ MT-Safe │
106 └────────────────────┴───────────────┴────────────────────┘
108 POSIX.1-2001, POSIX.1-2008, SVr4. The function tdestroy() is a GNU
109 extension.
110
112 twalk() takes a pointer to the root, while the other functions take a
113 pointer to a variable which points to the root.
114 tdelete() frees the memory required for the node in the tree. The user
116 is responsible for freeing the memory for the corresponding data.
117 The example program depends on the fact that twalk() makes no further
119 reference to a node after calling the user function with argument
120 "endorder" or "leaf". This works with the GNU library implementation,
121 but is not in the System V documentation.
122
124 The following program inserts twelve random numbers into a binary tree,
125 where duplicate numbers are collapsed, then prints the numbers in
126 order.
127 #define _GNU_SOURCE /* Expose declaration of tdestroy() */
129 #include <search.h>
130 #include <stdlib.h>
131 #include <stdio.h>
132 #include <time.h>
133 static void *root = NULL;
135 static void *
137 xmalloc(unsigned n)
138 {
139 void *p;
140 p = malloc(n);
141 if (p)
142 return p;
143 fprintf(stderr, "insufficient memory\n");
144 exit(EXIT_FAILURE);
145 }
146 static int
148 compare(const void *pa, const void *pb)
149 {
150 if (*(int *) pa < *(int *) pb)
151 return -1;
152 if (*(int *) pa > *(int *) pb)
153 return 1;
154 return 0;
155 }
156 static void
158 action(const void *nodep, const VISIT which, const int depth)
159 {
160 int *datap;
161 switch (which) {
163 case preorder:
164 break;
165 case postorder:
166 datap = *(int **) nodep;
167 printf("%6d\n", *datap);
168 break;
169 case endorder:
170 break;
171 case leaf:
172 datap = *(int **) nodep;
173 printf("%6d\n", *datap);
174 break;
175 }
176 }
177 int
179 main(void)
180 {
181 int i, *ptr;
182 void *val;
183 srand(time(NULL));
185 for (i = 0; i < 12; i++) {
186 ptr = xmalloc(sizeof(int));
187 *ptr = rand() & 0xff;
188 val = tsearch((void *) ptr, &root, compare);
189 if (val == NULL)
190 exit(EXIT_FAILURE);
191 else if ((*(int **) val) != ptr)
192 free(ptr);
193 }
194 twalk(root, action);
195 tdestroy(root, free);
196 exit(EXIT_SUCCESS);
197 }
198
200 bsearch(3), hsearch(3), lsearch(3), qsort(3)
201
203 This page is part of release 4.15 of the Linux man-pages project. A
204 description of the project, information about reporting bugs, and the
205 latest version of this page, can be found at
206 https://www.kernel.org/doc/man-pages/.
207GNU 2015-08-08 TSEARCH(3)