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man:twalk

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

NAME

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

SYNOPSIS

     #include <search.h>
     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,
                                        const VISIT which,
                                        const int depth));
     #define _GNU_SOURCE         /* See feature_test_macros(7) */
     #include <search.h>
     void tdestroy(void *root, void (*free_node)(void *nodep));

DESCRIPTION

     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
     return an integer which is negative, zero, or  positive,  depending  on
     whether the first item is less than, equal to, or greater than the sec-
     ond.
     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
     zero.
     (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.)
     tdestroy()  removes  the  whole  tree  pointed  to by root, freeing all
     resources 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.

RETURN VALUE

     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
     entry.

ATTRIBUTES

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).
     allbox;  lb  lb  lb  l  l  l.   Interface Attribute Value T{ tsearch(),
     tfind(),
     tdelete() T}   Thread safety  MT-Safe race:rootp T{ twalk() T}   Thread
     safety  MT-Safe race:root T{ tdestroy() T}   Thread safety  MT-Safe

CONFORMING TO

     POSIX.1-2001,  POSIX.1-2008,  SVr4.   The  function tdestroy() is a GNU
     extension.

NOTES

     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
     "endorder" or "leaf".  This works with the GNU library  implementation,
     but is not in the System V documentation.

EXAMPLE

     The following program inserts twelve random numbers into a binary tree,
     where duplicate numbers are  collapsed,  then  prints  the  numbers  in
     order.
     #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");
         exit(EXIT_FAILURE); }
     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,  const  VISIT  which,  const  int
     depth) {
         int *datap;
         switch (which) {
         case preorder:
             break;
         case postorder:
             datap = *(int **) nodep;
             printf("%6d\n", *datap);
             break;
         case endorder:
             break;
         case leaf:
             datap = *(int **) nodep;
             printf("%6d\n", *datap);
             break;
         } }
     int main(void) {
         int i, *ptr;
         void *val;
         srand(time(NULL));
         for (i = 0; i < 12; i++) {
             ptr = xmalloc(sizeof(int));
             *ptr = rand() & 0xff;
             val = tsearch((void *) ptr, &root, compare);
             if (val == NULL)
                 exit(EXIT_FAILURE);
             else if ((*(int **) val) != ptr)
                 free(ptr);
         }
         twalk(root, action);
         tdestroy(root, free);
         exit(EXIT_SUCCESS); }

SEE ALSO

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

COLOPHON

     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

GNU 2018-04-30 TSEARCH(3)

/data/webs/external/dokuwiki/data/pages/man/twalk.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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