tsearch

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



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

SYNOPSIS
       #include <search.h>

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

       void *tfind(const void *key, const void **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
       #include <search.h>

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

DESCRIPTION
       tsearch, tfind, twalk, and tdelete manage a binary tree.  They are gen-
       eralized 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 inte-
       ger which is negative, zero, or  positive,  depending  on  whether  the
       first item is less than, equal to, or greater than the second.

       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 it.  If it is not found, then tsearch adds it, and
       returns a pointer to the newly added item.

       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 is a pointer to the node being vis-
       ited.  The second is an integer which takes  on  the  values  preorder,
       postorder, and endorder depending on whether this is the first, second,
       or third visit to the internal node, or leaf if it is the single  visit
       to  a leaf node.  (These symbols are defined in <search.h>.)  The third
       argument is the depth of the node,  with  zero  being  the  root.   You
       should not modify the tree while traversing it as the the results would
       be undefined.

       tdestroy removes the whole  tree  pointed  to  by  rootp,  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.  It is called in  any
       case.

       (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.)

RETURN VALUE
       tsearch returns a pointer to a matching item in the  tree,  or  to  the
       newly  added  item, or NULL if there was insufficient memory to add the
       item.  tfind returns a pointer to the item, or  NULL  if  no  match  is
       found.   If there are multiple elements that match the key, the element
       returned is unspecified.

       tdelete returns a pointer to the parent of the item deleted, or NULL if
       the item was not found.

       tsearch,  tfind,  and  tdelete  also  return  NULL if rootp was NULL on
       entry.

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

       twalk  uses  postorder  to mean "after the left subtree, but before the
       right subtree".   Some  authorities  would  call  this  "inorder",  and
       reserve "postorder" to mean "after both subtrees".

       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 SysV documentation.

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

           #include <search.h>
           #include <stdlib.h>
           #include <stdio.h>
           #include <time.h>

           void *root=NULL;

           void *xmalloc(unsigned n) {
             void *p;
             p = malloc(n);
             if(p) return p;
             fprintf(stderr, "insufficient memory\n");
             exit(1);
           }

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

           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() {
             int i, *ptr;
             void *val;

             srand(time(NULL));
             for (i = 0; i < 12; i++) {
                 ptr = (int *)xmalloc(sizeof(int));
                 *ptr = rand()&0xff;
                 val = tsearch((void *)ptr, &root, compare);
                 if(val == NULL) exit(1);
             }
             twalk(root, action);
             return 0;
           }

CONFORMING TO
       SVID.  The function tdestroy() is a GNU extension.

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




GNU                               1995-09-24                        TSEARCH(3)