1TDELETE(P) POSIX Programmer's Manual TDELETE(P)
2
6 tdelete, tfind, tsearch, twalk - manage a binary search tree
7
9 #include <search.h>
10 void *tdelete(const void *restrict key, void **restrict rootp,
12 int(*compar)(const void *, const void *));
13 void *tfind(const void *key, void *const *rootp,
14 int(*compar)(const void *, const void *));
15 void *tsearch(const void *key, void **rootp,
16 int (*compar)(const void *, const void *));
17 void twalk(const void *root,
18 void (*action)(const void *, VISIT, int));
19
22 The tdelete(), tfind(), tsearch(), and twalk() functions manipulate
23 binary search trees. Comparisons are made with a user-supplied routine,
24 the address of which is passed as the compar argument. This routine is
25 called with two arguments, which are the pointers to the elements being
26 compared. The application shall ensure that the user-supplied routine
27 returns an integer less than, equal to, or greater than 0, according to
28 whether the first argument is to be considered less than, equal to, or
29 greater than the second argument. The comparison function need not com‐
30 pare every byte, so arbitrary data may be contained in the elements in
31 addition to the values being compared.
32 The tsearch() function shall build and access the tree. The key argu‐
34 ment is a pointer to an element to be accessed or stored. If there is a
35 node in the tree whose element is equal to the value pointed to by key,
36 a pointer to this found node shall be returned. Otherwise, the value
37 pointed to by key shall be inserted (that is, a new node is created and
38 the value of key is copied to this node), and a pointer to this node
39 returned. Only pointers are copied, so the application shall ensure
40 that the calling routine stores the data. The rootp argument points to
41 a variable that points to the root node of the tree. A null pointer
42 value for the variable pointed to by rootp denotes an empty tree; in
43 this case, the variable shall be set to point to the node which shall
44 be at the root of the new tree.
45 Like tsearch(), tfind() shall search for a node in the tree, returning
47 a pointer to it if found. However, if it is not found, tfind() shall
48 return a null pointer. The arguments for tfind() are the same as for
49 tsearch().
50 The tdelete() function shall delete a node from a binary search tree.
52 The arguments are the same as for tsearch(). The variable pointed to
53 by rootp shall be changed if the deleted node was the root of the tree.
54 The tdelete() function shall return a pointer to the parent of the
55 deleted node, or a null pointer if the node is not found.
56 The twalk() function shall traverse a binary search tree. The root
58 argument is a pointer to the root node of the tree to be traversed.
59 (Any node in a tree may be used as the root for a walk below that
60 node.) The argument action is the name of a routine to be invoked at
61 each node. This routine is, in turn, called with three arguments. The
62 first argument shall be the address of the node being visited. The
63 structure pointed to by this argument is unspecified and shall not be
64 modified by the application, but it shall be possible to cast a
65 pointer-to-node into a pointer-to-pointer-to-element to access the ele‐
66 ment stored in the node. The second argument shall be a value from an
67 enumeration data type:
68 typedef enum { preorder, postorder, endorder, leaf } VISIT;
71 (defined in <search.h>), depending on whether this is the first, sec‐
73 ond, or third time that the node is visited (during a depth-first,
74 left-to-right traversal of the tree), or whether the node is a leaf.
75 The third argument shall be the level of the node in the tree, with the
76 root being level 0.
77 If the calling function alters the pointer to the root, the result is
79 undefined.
80
82 If the node is found, both tsearch() and tfind() shall return a pointer
83 to it. If not, tfind() shall return a null pointer, and tsearch() shall
84 return a pointer to the inserted item.
85 A null pointer shall be returned by tsearch() if there is not enough
87 space available to create a new node.
88 A null pointer shall be returned by tdelete(), tfind(), and tsearch()
90 if rootp is a null pointer on entry.
91 The tdelete() function shall return a pointer to the parent of the
93 deleted node, or a null pointer if the node is not found.
94 The twalk() function shall not return a value.
96
98 No errors are defined.
99 The following sections are informative.
101
103 The following code reads in strings and stores structures containing a
104 pointer to each string and a count of its length. It then walks the
105 tree, printing out the stored strings and their lengths in alphabetical
106 order.
107 #include <search.h>
110 #include <string.h>
111 #include <stdio.h>
112 #define STRSZ 10000
115 #define NODSZ 500
116 struct node { /* Pointers to these are stored in the tree. */
119 char *string;
120 int length;
121 };
122 char string_space[STRSZ]; /* Space to store strings. */
125 struct node nodes[NODSZ]; /* Nodes to store. */
126 void *root = NULL; /* This points to the root. */
127 int main(int argc, char *argv[])
130 {
131 char *strptr = string_space;
132 struct node *nodeptr = nodes;
133 void print_node(const void *, VISIT, int);
134 int i = 0, node_compare(const void *, const void *);
135 while (gets(strptr) != NULL && i++ < NODSZ) {
138 /* Set node. */
139 nodeptr->string = strptr;
140 nodeptr->length = strlen(strptr);
141 /* Put node into the tree. */
142 (void) tsearch((void *)nodeptr, (void **)&root,
143 node_compare);
144 /* Adjust pointers, so we do not overwrite tree. */
145 strptr += nodeptr->length + 1;
146 nodeptr++;
147 }
148 twalk(root, print_node);
149 return 0;
150 }
151 /*
154 * This routine compares two nodes, based on an
155 * alphabetical ordering of the string field.
156 */
157 int
158 node_compare(const void *node1, const void *node2)
159 {
160 return strcmp(((const struct node *) node1)->string,
161 ((const struct node *) node2)->string);
162 }
163 /*
166 * This routine prints out a node, the second time
167 * twalk encounters it or if it is a leaf.
168 */
169 void
170 print_node(const void *ptr, VISIT order, int level)
171 {
172 const struct node *p = *(const struct node **) ptr;
173 if (order == postorder || order == leaf) {
176 (void) printf("string = %s, length = %d\n",
177 p->string, p->length);
178 }
179 }
180
182 The root argument to twalk() is one level of indirection less than the
183 rootp arguments to tdelete() and tsearch().
184 There are two nomenclatures used to refer to the order in which tree
186 nodes are visited. The tsearch() function uses preorder, postorder, and
187 endorder to refer respectively to visiting a node before any of its
188 children, after its left child and before its right, and after both its
189 children. The alternative nomenclature uses preorder, inorder, and
190 postorder to refer to the same visits, which could result in some con‐
191 fusion over the meaning of postorder.
192
194 None.
195
197 None.
198
200 hcreate() , lsearch() , the Base Definitions volume of
201 IEEE Std 1003.1-2001, <search.h>
202
204 Portions of this text are reprinted and reproduced in electronic form
205 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
206 -- Portable Operating System Interface (POSIX), The Open Group Base
207 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
208 Electrical and Electronics Engineers, Inc and The Open Group. In the
209 event of any discrepancy between this version and the original IEEE and
210 The Open Group Standard, the original IEEE and The Open Group Standard
211 is the referee document. The original Standard can be obtained online
212 at http://www.opengroup.org/unix/online.html .
213IEEE/The Open Group 2003 TDELETE(P)