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

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

       #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));

       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 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 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 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.)

       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.

       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

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

       |Interface	    | Attribute	    | Value		 |
       |tsearch(), tfind(), | Thread safety | MT-Safe race:rootp |
       |tdelete()	    |		    |			 |
       |twalk()		    | Thread safety | MT-Safe race:root	 |
       |tdestroy()	    | Thread safety | MT-Safe		 |
       POSIX.1-2001, POSIX.1-2008, SVr4.  The function	tdestroy()  is	a  GNU

       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.

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

       #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, const VISIT which, const 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)

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GNU				  2015-08-08			    TSEARCH(3)