• 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 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 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 visited.
  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.
  
  
  
  (More commonly, preorder, postorder, and endorder
  are known as preorder, inorder, and postorder:
  before visiting the children, after the first and before the second,
  and after visiting the children.
  Thus, the choice of name post%order
  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 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.
  
• CONFORMING TO
  
  SVr4, POSIX.1-2001.
  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.
  
  
  
  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 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>
  
  void *root = NULL;
  
  void *
  xmalloc(unsigned n)
  {
      void *p;
      p = malloc(n);
      if (p)
          return p;
      fprintf(stderr, "insufficient memory\n");
      exit(EXIT_FAILURE);
  }
  
  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(void)
  {
      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(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) , feature_test_macros(7)
• COLOPHON
  
  This page is part of release 3.19 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Current Users: 126 © 1999-2009 PenguinSoft. All trademarks and copyrights on this page are owned by their respective companies. Linux is a trademark of Linus Torvalds.