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

       tsearch, tfind, tdelete, twalk - 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, 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));

       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  corre-
       sponding 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 pos-
       torder:	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 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 nec-
       essary 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

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

       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 sub-

       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.

       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");

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

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

	     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;

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

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

GNU					    1995-09-24				       TSEARCH(3)
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