man3/tsearch.3

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  25 .TH TSEARCH 3  2018-04-30 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 tsearch, tfind, tdelete, twalk, tdestroy \- manage a binary search tree
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <search.h>
  31 .PP
  32 .BI "typedef enum { preorder, postorder, endorder, leaf } VISIT;"
  33 .PP
  34 .BI "void *tsearch(const void *" key ", void **" rootp ,
  35 .BI "                int (*" compar ")(const void *, const void *));"
  36 .PP
  37 .BI "void *tfind(const void *" key ", void *const *" rootp ,
  38 .BI "                int (*" compar ")(const void *, const void *));"
  39 .PP
  40 .BI "void *tdelete(const void *" key ", void **" rootp ,
  41 .BI "                int (*" compar ")(const void *, const void *));"
  42 .PP
  43 .BI "void twalk(const void *" root ", void (*" action ")(const void *" nodep ,
  44 .BI "                                   VISIT " which ", int " depth "));"
  45 .PP
  46 .BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
  47 .B #include <search.h>
  48 .PP
  49 .BI "void twalk_r(const void *" root ", void (*" action ")(const void *" np ,
  50 .BI "                                   VISIT " which ", void *" closure "),
  51 .BI "                                   void *" closure );
  52 .PP
  53 .BI "void tdestroy(void *" root ", void (*" free_node ")(void *" nodep ));
  54 .fi
  55 .SH DESCRIPTION
  56 .BR tsearch (),
  57 .BR tfind (),
  58 .BR twalk (),
  59 and
  60 .BR tdelete ()
  61 manage a
  62 binary search tree.
  63 They are generalized from Knuth (6.2.2) Algorithm T.
  64 The first field in each node of the tree is a pointer to the
  65 corresponding data item.
  66 (The calling program must store the actual data.)
  67 .I compar
  68 points to a comparison routine, which takes
  69 pointers to two items.
  70 It should return an integer which is negative,
  71 zero, or positive, depending on whether the first item is less than,
  72 equal to, or greater than the second.
  73 .PP
  74 .BR tsearch ()
  75 searches the tree for an item.
  76 .I key
  77 points to the item to be searched for.
  78 .I rootp
  79 points to a variable which points to the root of the tree.
  80 If the tree is empty,
  81 then the variable that
  82 .I rootp
  83 points to should be set to NULL.
  84 If the item is found in the tree, then
  85 .BR tsearch ()
  86 returns a pointer
  87 to the corresponding tree node.
  88 (In other words,
  89 .BR tsearch ()
  90 returns a pointer to a pointer to the data item.)
  91 If the item is not found, then
  92 .BR tsearch ()
  93 adds it, and returns a
  94 pointer to the corresponding tree node.
  95 .PP
  96 .BR tfind ()
  97 is like
  98 .BR tsearch (),
  99 except that if the item is not
 100 found, then
 101 .BR tfind ()
 102 returns NULL.
 103 .PP
 104 .BR tdelete ()
 105 deletes an item from the tree.
 106 Its arguments are the same as for
 107 .BR tsearch ().
 108 .PP
 109 .BR twalk ()
 110 performs depth-first, left-to-right traversal of a binary
 111 tree.
 112 .I root
 113 points to the starting node for the traversal.
 114 If that node is not the root, then only part of the tree will be visited.
 115 .BR twalk ()
 116 calls the user function
 117 .I action
 118 each time a node is
 119 visited (that is, three times for an internal node, and once for a
 120 leaf).
 121 .IR action ,
 122 in turn, takes three arguments.
 123 The first argument is a pointer to the node being visited.
 124 The structure of the node is unspecified,
 125 but it is possible to cast the pointer to a pointer-to-pointer-to-element
 126 in order to access the element stored within the node.
 127 The application must not modify the structure pointed to by this argument.
 128 The second argument is an integer which
 129 takes one of the values
 130 .BR preorder ,
 131 .BR postorder ,
 132 or
 133 .B endorder
 134 depending on whether this is the first, second, or
 135 third visit to the internal node,
 136 or the value
 137 .B leaf
 138 if this is the single visit to a leaf node.
 139 (These symbols are defined in
 140 .IR <search.h> .)
 141 The third argument is the depth of the node;
 142 the root node has depth zero.
 143 .PP
 144 (More commonly,
 145 .BR preorder ,
 146 .BR postorder ,
 147 and
 148 .B endorder
 149 are known as
 150 .BR preorder ,
 151 .BR inorder ,
 152 and
 153 .BR postorder :
 154 before visiting the children, after the first and before the second,
 155 and after visiting the children.
 156 Thus, the choice of name
 157 .B post\%order
 158 is rather confusing.)
 159 .PP
 160 .BR twalk_r ()
 161 is similar to
 162 .BR twalk (),
 163 but instead of the
 164 .I depth
 165 argument, the
 166 .I closure
 167 argument pointer is passed to each invocation of the action callback,
 168 unchanged.
 169 This pointer can be used to pass information to and from
 170 the callback function in a thread-safe fashion, without resorting
 171 to global variables.
 172 .PP
 173 .BR tdestroy ()
 174 removes the whole tree pointed to by
 175 .IR root ,
 176 freeing all resources allocated by the
 177 .BR tsearch ()
 178 function.
 179 For the data in each tree node the function
 180 .I free_node
 181 is called.
 182 The pointer to the data is passed as the argument to the function.
 183 If no such work is necessary,
 184 .I free_node
 185 must point to a function
 186 doing nothing.
 187 .SH RETURN VALUE
 188 .BR tsearch ()
 189 returns a pointer to a matching node in the tree, or to
 190 the newly added node, or NULL if there was insufficient memory
 191 to add the item.
 192 .BR tfind ()
 193 returns a pointer to the node, or
 194 NULL if no match is found.
 195 If there are multiple items that match the key,
 196 the item whose node is returned is unspecified.
 197 .PP
 198 .BR tdelete ()
 199 returns a pointer to the parent of the node deleted, or
 200 NULL if the item was not found.
 201 If the deleted node was the root node,
 202 .BR tdelete ()
 203 returns a dangling pointer that must not be accessed.
 204 .PP
 205 .BR tsearch (),
 206 .BR tfind (),
 207 and
 208 .BR tdelete ()
 209 also
 210 return NULL if
 211 .I rootp
 212 was NULL on entry.
 213 .SH VERSIONS
 214 .BR twalk_r ()
 215 is available in glibc since version 2.30.
 216 .SH ATTRIBUTES
 217 For an explanation of the terms used in this section, see
 218 .BR attributes (7).
 219 .TS
 220 allbox;
 221 lb lb lb
 222 l l l.
 223 Interface       Attribute       Value
 224 T{
 225 .BR tsearch (),
 226 .BR tfind (),
 227 .br
 228 .BR tdelete ()
 229 T}      Thread safety   MT-Safe race:rootp
 230 T{
 231 .BR twalk ()
 232 T}      Thread safety   MT-Safe race:root
 233 T{
 234 .BR twalk_r ()
 235 T}      Thread safety   MT-Safe race:root
 236 T{
 237 .BR tdestroy ()
 238 T}      Thread safety   MT-Safe
 239 .TE
 240 .SH CONFORMING TO
 241 POSIX.1-2001, POSIX.1-2008, SVr4.
 242 The functions
 243 .BR tdestroy ()
 244 and
 245 .BR twalk_r ()
 246 are GNU extensions.
 247 .SH NOTES
 248 .BR twalk ()
 249 takes a pointer to the root, while the other functions
 250 take a pointer to a variable which points to the root.
 251 .PP
 252 .BR tdelete ()
 253 frees the memory required for the node in the tree.
 254 The user is responsible for freeing the memory for the corresponding
 255 data.
 256 .PP
 257 The example program depends on the fact that
 258 .BR twalk ()
 259 makes no
 260 further reference to a node after calling the user function with
 261 argument "endorder" or "leaf".
 262 This works with the GNU library
 263 implementation, but is not in the System V documentation.
 264 .SH EXAMPLE
 265 The following program inserts twelve random numbers into a binary
 266 tree, where duplicate numbers are collapsed, then prints the numbers
 267 in order.
 268 .PP
 269 .EX
 270 #define _GNU_SOURCE     /* Expose declaration of tdestroy() */
 271 #include <search.h>
 272 #include <stdlib.h>
 273 #include <stdio.h>
 274 #include <time.h>
 275
 276 static void *root = NULL;
 277
 278 static void *
 279 xmalloc(unsigned n)
 280 {
 281     void *p;
 282     p = malloc(n);
 283     if (p)
 284         return p;
 285     fprintf(stderr, "insufficient memory\en");
 286     exit(EXIT_FAILURE);
 287 }
 288
 289 static int
 290 compare(const void *pa, const void *pb)
 291 {
 292     if (*(int *) pa < *(int *) pb)
 293         return \-1;
 294     if (*(int *) pa > *(int *) pb)
 295         return 1;
 296     return 0;
 297 }
 298
 299 static void
 300 action(const void *nodep, VISIT which, int depth)
 301 {
 302     int *datap;
 303
 304     switch (which) {
 305     case preorder:
 306         break;
 307     case postorder:
 308         datap = *(int **) nodep;
 309         printf("%6d\en", *datap);
 310         break;
 311     case endorder:
 312         break;
 313     case leaf:
 314         datap = *(int **) nodep;
 315         printf("%6d\en", *datap);
 316         break;
 317     }
 318 }
 319
 320 int
 321 main(void)
 322 {
 323     int i, *ptr;
 324     void *val;
 325
 326     srand(time(NULL));
 327     for (i = 0; i < 12; i++) {
 328         ptr = xmalloc(sizeof(int));
 329         *ptr = rand() & 0xff;
 330         val = tsearch((void *) ptr, &root, compare);
 331         if (val == NULL)
 332             exit(EXIT_FAILURE);
 333         else if ((*(int **) val) != ptr)
 334             free(ptr);
 335     }
 336     twalk(root, action);
 337     tdestroy(root, free);
 338     exit(EXIT_SUCCESS);
 339 }
 340 .EE
 341 .SH SEE ALSO
 342 .BR bsearch (3),
 343 .BR hsearch (3),
 344 .BR lsearch (3),
 345 .BR qsort (3)