TSEARCH(3)                 Linux Programmer's Manual                TSEARCH(3)

       tsearch, tfind, tdelete, twalk, tdestroy - manage a binary search tree

       #include <search.h>

       typedef enum { preorder, postorder, endorder, leaf } VISIT;

       void *tsearch(const void *key, void **rootp,
                       int (*compar)(const void *, const void *));

       void *tfind(const void *key, void *const *rootp,
                       int (*compar)(const void *, const void *));

       void *tdelete(const void *key, void **rootp,
                       int (*compar)(const void *, const void *));

       void twalk(const void *root,
                       void (*action)(const void *nodep, VISIT which,
                                      int depth));

       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <search.h>

       void twalk_r(const void *root,
                       void (*action)(const void *nodep, VISIT which,
                                      void *closure),
                       void *closure);

       void tdestroy(void *root, void (*free_node)(void *nodep));

       tsearch(), tfind(), twalk(), and tdelete() manage a binary search tree.
       They are generalized from Knuth (6.2.2) Algorithm T.  The  first  field
       in  each  node of the tree is a pointer to the corresponding data item.
       (The calling program must store the actual data.)  compar points  to  a
       comparison  routine,  which takes pointers to two items.  It should re-
       turn an integer which is negative,  zero,  or  positive,  depending  on
       whether the first item is less than, equal to, or greater than the sec-

       tsearch() searches the tree for an item.  key points to the item to  be
       searched  for.   rootp points to a variable which points to the root of
       the tree.  If the tree is empty, then the variable that rootp points to
       should  be  set  to  NULL.   If  the  item  is  found in the tree, then
       tsearch() returns a pointer to the corresponding tree node.  (In  other
       words,  tsearch() returns a pointer to a pointer to the data item.)  If
       the item is not found, then tsearch() adds it, and returns a pointer to
       the corresponding tree node.

       tfind()  is  like tsearch(), except that if the item is not found, then
       tfind() returns NULL.

       tdelete() deletes an item from the tree.  Its arguments are the same as
       for tsearch().

       twalk() performs depth-first, left-to-right traversal of a binary tree.
       root points to the starting node for the traversal.  If  that  node  is
       not  the  root,  then  only  part of the tree will be visited.  twalk()
       calls the user function action each time a node is  visited  (that  is,
       three  times  for  an  internal node, and once for a leaf).  action, in
       turn, takes three arguments.  The first argument is a  pointer  to  the
       node  being  visited.  The structure of the node is unspecified, but it
       is possible to cast the pointer to a  pointer-to-pointer-to-element  in
       order  to  access  the element stored within the node.  The application
       must not modify the structure pointed to by this argument.  The  second
       argument  is  an  integer  which takes one of the values preorder, pos-
       torder, or endorder depending on whether this is the first, second,  or
       third visit to the internal node, or the value leaf if this is the sin-
       gle visit to a leaf node.  (These symbols are defined  in  <search.h>.)
       The  third  argument  is the depth of the node; the root node has depth

       (More commonly, preorder, postorder, and endorder  are  known  as  pre-
       order,  inorder, and postorder: before visiting the children, after the
       first and before the second, and after visiting  the  children.   Thus,
       the choice of name postorder is rather confusing.)

       twalk_r() is similar to twalk(), but instead of the depth argument, the
       closure argument pointer is passed to each  invocation  of  the  action
       callback,  unchanged.   This pointer can be used to pass information to
       and from the callback function in a thread-safe  fashion,  without  re-
       sorting to global variables.

       tdestroy()  removes  the whole tree pointed to by root, freeing all re-
       sources allocated by the tsearch() function.  For the data in each tree
       node  the  function  free_node  is  called.  The pointer to the data is
       passed as the argument to the function.  If no such work is  necessary,
       free_node must point to a function doing nothing.

       tsearch()  returns  a pointer to a matching node in the tree, or to the
       newly added node, or NULL if there was insufficient memory to  add  the
       item.   tfind()  returns  a pointer to the node, or NULL if no match is
       found.  If there are multiple items that match the key, the item  whose
       node is returned is unspecified.

       tdelete()  returns a pointer to the parent of the node deleted, or NULL
       if the item was not found.  If the deleted  node  was  the  root  node,
       tdelete() returns a dangling pointer that must not be accessed.

       tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL on

       twalk_r() is available in glibc since version 2.30.

       For an  explanation  of  the  terms  used  in  this  section,  see  at-

       |Interface           | Attribute     | Value              |
       |tsearch(), tfind(), | Thread safety | MT-Safe race:rootp |
       |tdelete()           |               |                    |
       |twalk()             | Thread safety | MT-Safe race:root  |
       |twalk_r()           | Thread safety | MT-Safe race:root  |
       |tdestroy()          | Thread safety | MT-Safe            |
       POSIX.1-2001,   POSIX.1-2008,   SVr4.   The  functions  tdestroy()  and
       twalk_r() are GNU extensions.

       twalk() takes a pointer to the root, while the other functions  take  a
       pointer to a variable which points to the root.

       tdelete() frees the memory required for the node in the tree.  The user
       is responsible for freeing the memory for the corresponding data.

       The example program depends on the fact that twalk() makes  no  further
       reference  to a node after calling the user function with argument "en-
       dorder" or "leaf".  This works with the GNU library implementation, but
       is not in the System V documentation.

       The following program inserts twelve random numbers into a binary tree,
       where duplicate numbers are collapsed, then prints the numbers  in  or-

       #define _GNU_SOURCE     /* Expose declaration of tdestroy() */
       #include <search.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <time.h>

       static void *root = NULL;

       static void *
       xmalloc(unsigned n)
           void *p;
           p = malloc(n);
           if (p)
               return p;
           fprintf(stderr, "insufficient memory\n");

       static int
       compare(const void *pa, const void *pb)
           if (*(int *) pa < *(int *) pb)
               return -1;
           if (*(int *) pa > *(int *) pb)
               return 1;
           return 0;

       static void
       action(const void *nodep, VISIT which, int depth)
           int *datap;

           switch (which) {
           case preorder:
           case postorder:
               datap = *(int **) nodep;
               printf("%6d\n", *datap);
           case endorder:
           case leaf:
               datap = *(int **) nodep;
               printf("%6d\n", *datap);

           int i, *ptr;
           void *val;

           for (i = 0; i < 12; i++) {
               ptr = xmalloc(sizeof(int));
               *ptr = rand() & 0xff;
               val = tsearch((void *) ptr, &root, compare);
               if (val == NULL)
               else if ((*(int **) val) != ptr)
           twalk(root, action);
           tdestroy(root, free);

       bsearch(3), hsearch(3), lsearch(3), qsort(3)

       This  page  is  part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
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GNU                               2019-05-09                        TSEARCH(3)
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