man3/tsearch.3

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  25 .TH TSEARCH 3  2015-08-08 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 tsearch, tfind, tdelete, twalk, tdestroy \- manage a binary tree
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <search.h>
  31 .sp
  32 .BI "void *tsearch(const void *" key ", void **" rootp ,
  33 .BI "                int (*" compar ")(const void *, const void *));"
  34 .sp
  35 .BI "void *tfind(const void *" key ", void *const *" rootp ,
  36 .BI "                int (*" compar ")(const void *, const void *));"
  37 .sp
  38 .BI "void *tdelete(const void *" key ", void **" rootp ,
  39 .BI "                int (*" compar ")(const void *, const void *));"
  40 .sp
  41 .BI "void twalk(const void *" root ", void (*" action ")(const void *" nodep ,
  42 .BI "                                   const VISIT " which ,
  43 .BI "                                   const int " depth "));"
  44 .sp
  45 .BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
  46 .br
  47 .B #include <search.h>
  48 .sp
  49 .BI "void tdestroy(void *" root ", void (*" free_node ")(void *" nodep ));
  50 .fi
  51 .SH DESCRIPTION
  52 .BR tsearch (),
  53 .BR tfind (),
  54 .BR twalk (),
  55 and
  56 .BR tdelete ()
  57 manage a
  58 binary tree.
  59 They are generalized from Knuth (6.2.2) Algorithm T.
  60 The first field in each node of the tree is a pointer to the
  61 corresponding data item.
  62 (The calling program must store the actual data.)
  63 .IR compar
  64 points to a comparison routine, which takes
  65 pointers to two items.
  66 It should return an integer which is negative,
  67 zero, or positive, depending on whether the first item is less than,
  68 equal to, or greater than the second.
  69 .PP
  70 .BR tsearch ()
  71 searches the tree for an item.
  72 .IR key
  73 points to the item to be searched for.
  74 .IR rootp
  75 points to a variable which points to the root of the tree.
  76 If the tree is empty,
  77 then the variable that
  78 .IR rootp
  79 points to should be set to NULL.
  80 If the item is found in the tree, then
  81 .BR tsearch ()
  82 returns a pointer
  83 to it.
  84 If it is not found, then
  85 .BR tsearch ()
  86 adds it, and returns a
  87 pointer to the newly added item.
  88 .PP
  89 .BR tfind ()
  90 is like
  91 .BR tsearch (),
  92 except that if the item is not
  93 found, then
  94 .BR tfind ()
  95 returns NULL.
  96 .PP
  97 .BR tdelete ()
  98 deletes an item from the tree.
  99 Its arguments are the same as for
 100 .BR tsearch ().
 101 .PP
 102 .BR twalk ()
 103 performs depth-first, left-to-right traversal of a binary
 104 tree.
 105 .IR root
 106 points to the starting node for the traversal.
 107 If that node is not the root, then only part of the tree will be visited.
 108 .BR twalk ()
 109 calls the user function
 110 .IR action
 111 each time a node is
 112 visited (that is, three times for an internal node, and once for a
 113 leaf).
 114 .IR action ,
 115 in turn, takes three arguments.
 116 The first argument is a pointer to the node being visited.
 117 The structure of the node is unspecified,
 118 but it is possible to cast the pointer to a pointer-to-pointer-to-element
 119 in order to access the element stored within the node.
 120 The application must not modify the structure pointed to by this argument.
 121 The second argument is an integer which
 122 takes one of the values
 123 .BR preorder ,
 124 .BR postorder ,
 125 or
 126 .BR endorder
 127 depending on whether this is the first, second, or
 128 third visit to the internal node,
 129 or the value
 130 .BR leaf
 131 if this is the single visit to a leaf node.
 132 (These symbols are defined in
 133 .IR <search.h> .)
 134 The third argument is the depth of the node;
 135 the root node has depth zero.
 136 .PP
 137 (More commonly,
 138 .BR preorder ,
 139 .BR postorder ,
 140 and
 141 .BR endorder
 142 are known as
 143 .BR preorder ,
 144 .BR inorder ,
 145 and
 146 .BR postorder :
 147 before visiting the children, after the first and before the second,
 148 and after visiting the children.
 149 Thus, the choice of name
 150 .BR post\%order
 151 is rather confusing.)
 152 .PP
 153 .BR tdestroy ()
 154 removes the whole tree pointed to by
 155 .IR root ,
 156 freeing all resources allocated by the
 157 .BR tsearch ()
 158 function.
 159 For the data in each tree node the function
 160 .IR free_node
 161 is called.
 162 The pointer to the data is passed as the argument to the function.
 163 If no such work is necessary,
 164 .IR free_node
 165 must point to a function
 166 doing nothing.
 167 .SH RETURN VALUE
 168 .BR tsearch ()
 169 returns a pointer to a matching item in the tree, or to
 170 the newly added item, or NULL if there was insufficient memory
 171 to add the item.
 172 .BR tfind ()
 173 returns a pointer to the item, or
 174 NULL if no match is found.
 175 If there are multiple elements that match the key,
 176 the element returned is unspecified.
 177 .PP
 178 .BR tdelete ()
 179 returns a pointer to the parent of the item deleted, or
 180 NULL if the item was not found.
 181 .PP
 182 .BR tsearch (),
 183 .BR tfind (),
 184 and
 185 .BR tdelete ()
 186 also
 187 return NULL if
 188 .IR rootp
 189 was NULL on entry.
 190 .SH ATTRIBUTES
 191 For an explanation of the terms used in this section, see
 192 .BR attributes (7).
 193 .TS
 194 allbox;
 195 lb lb lb
 196 l l l.
 197 Interface       Attribute       Value
 198 T{
 199 .BR tsearch (),
 200 .BR tfind (),
 201 .br
 202 .BR tdelete ()
 203 T}      Thread safety   MT-Safe race:rootp
 204 T{
 205 .BR twalk ()
 206 T}      Thread safety   MT-Safe race:root
 207 T{
 208 .BR tdestroy ()
 209 T}      Thread safety   MT-Safe
 210 .TE
 211 .SH CONFORMING TO
 212 POSIX.1-2001, POSIX.1-2008, SVr4.
 213 The function
 214 .BR tdestroy ()
 215 is a GNU extension.
 216 .SH NOTES
 217 .BR twalk ()
 218 takes a pointer to the root, while the other functions
 219 take a pointer to a variable which points to the root.
 220 .PP
 221 .BR tdelete ()
 222 frees the memory required for the node in the tree.
 223 The user is responsible for freeing the memory for the corresponding
 224 data.
 225 .PP
 226 The example program depends on the fact that
 227 .BR twalk ()
 228 makes no
 229 further reference to a node after calling the user function with
 230 argument "endorder" or "leaf".
 231 This works with the GNU library
 232 implementation, but is not in the System V documentation.
 233 .SH EXAMPLE
 234 The following program inserts twelve random numbers into a binary
 235 tree, where duplicate numbers are collapsed, then prints the numbers
 236 in order.
 237 .sp
 238 .nf
 239 #define _GNU_SOURCE     /* Expose declaration of tdestroy() */
 240 #include <search.h>
 241 #include <stdlib.h>
 242 #include <stdio.h>
 243 #include <time.h>
 244
 245 static void *root = NULL;
 246
 247 static void *
 248 xmalloc(unsigned n)
 249 {
 250     void *p;
 251     p = malloc(n);
 252     if (p)
 253         return p;
 254     fprintf(stderr, "insufficient memory\\n");
 255     exit(EXIT_FAILURE);
 256 }
 257
 258 static int
 259 compare(const void *pa, const void *pb)
 260 {
 261     if (*(int *) pa < *(int *) pb)
 262         return \-1;
 263     if (*(int *) pa > *(int *) pb)
 264         return 1;
 265     return 0;
 266 }
 267
 268 static void
 269 action(const void *nodep, const VISIT which, const int depth)
 270 {
 271     int *datap;
 272
 273     switch (which) {
 274     case preorder:
 275         break;
 276     case postorder:
 277         datap = *(int **) nodep;
 278         printf("%6d\\n", *datap);
 279         break;
 280     case endorder:
 281         break;
 282     case leaf:
 283         datap = *(int **) nodep;
 284         printf("%6d\\n", *datap);
 285         break;
 286     }
 287 }
 288
 289 int
 290 main(void)
 291 {
 292     int i, *ptr;
 293     void *val;
 294
 295     srand(time(NULL));
 296     for (i = 0; i < 12; i++) {
 297         ptr = xmalloc(sizeof(int));
 298         *ptr = rand() & 0xff;
 299         val = tsearch((void *) ptr, &root, compare);
 300         if (val == NULL)
 301             exit(EXIT_FAILURE);
 302         else if ((*(int **) val) != ptr)
 303             free(ptr);
 304     }
 305     twalk(root, action);
 306     tdestroy(root, free);
 307     exit(EXIT_SUCCESS);
 308 }
 309 .fi
 310 .SH SEE ALSO
 311 .BR bsearch (3),
 312 .BR hsearch (3),
 313 .BR lsearch (3),
 314 .BR qsort (3)