TSEARCH(3)             FreeBSD Library Functions Manual             TSEARCH(3)

NAME
     tsearch, tfind, tdelete, twalk - manipulate binary search trees

SYNOPSIS
     #include <search.h>

     void *
     tdelete(const void * restrict key, posix_tnode ** restrict rootp,
         int (*compar) (const void *, const void *));

     posix_tnode *
     tfind(const void *key, posix_tnode * const *rootp,
         int (*compar) (const void *, const void *));

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

     void
     twalk(const posix_tnode *root,
         void (*action) (const posix_tnode *, VISIT, int));

DESCRIPTION
     The tdelete(), tfind(), tsearch(), and twalk() functions manage binary
     search trees.  This implementation uses a balanced AVL tree, which due to
     its strong theoretical limit on the height of the tree has the advantage
     of calling the comparison function relatively infrequently.

     The comparison function passed in by the user has the same style of
     return values as strcmp(3).

     The tfind() function searches for the datum matched by the argument key
     in the binary tree rooted at rootp, returning a pointer to the datum if
     it is found and NULL if it is not.

     The tsearch() function is identical to tfind() except that if no match is
     found, key is inserted into the tree and a pointer to it is returned.  If
     rootp points to a NULL value a new binary search tree is created.

     The tdelete() function deletes a node from the specified binary search
     tree and returns a pointer to the parent of the node to be deleted.  It
     takes the same arguments as tfind() and tsearch().  If the node to be
     deleted is the root of the binary search tree, rootp will be adjusted.

     The twalk() function walks the binary search tree rooted in root and
     calls the function action on each node.  The action function is called
     with three arguments: a pointer to the current node, a value from the
     enum typedef enum { preorder, postorder, endorder, leaf } VISIT;
     specifying the traversal type, and a node level (where level zero is the
     root of the tree).

RETURN VALUES
     The tsearch() function returns NULL if allocation of a new node fails
     (usually due to a lack of free memory).

     The tfind(), tsearch(), and tdelete() functions return NULL if rootp is
     NULL or the datum cannot be found.

     The twalk() function returns no value.

EXAMPLES
     This example uses tsearch() to search for four strings in root.  Because
     the strings are not already present, they are added.  tsearch() is called
     twice on the fourth string to demonstrate that a string is not added when
     it is already present.  tfind() is used to find the single instance of
     the fourth string, and tdelete() removes it.  Finally, twalk() is used to
     return and display the resulting binary search tree.

     #include <stdio.h>
     #include <search.h>
     #include <string.h>

     int
     comp(const void *a, const void *b)
     {

             return strcmp(a, b);
     }

     void
     printwalk(const posix_tnode * node, VISIT v, int __unused0)
     {

             if (v == postorder || v == leaf) {
                     printf("node: %s\n", *(char **)node);
             }
     }

     int
     main(void)
     {
             posix_tnode *root = NULL;

             char one[] = "blah1";
             char two[] = "blah-2";
             char three[] = "blah-3";
             char four[] = "blah-4";

             tsearch(one, &root, comp);
             tsearch(two, &root, comp);
             tsearch(three, &root, comp);
             tsearch(four, &root, comp);
             tsearch(four, &root, comp);
             printf("four: %s\n", *(char **)tfind(four, &root, comp));
             tdelete(four, &root, comp);

             twalk(root, printwalk);
             return 0;
     }

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

STANDARDS
     These functions conform to IEEE Std 1003.1-2008 ("POSIX.1").

     The posix_tnode type is not part of IEEE Std 1003.1-2008 ("POSIX.1"), but
     is expected to be standardized by future versions of the standard.  It is
     defined as void for source-level compatibility.  Using posix_tnode makes
     distinguishing between nodes and keys easier.

FreeBSD 13.1-RELEASE-p6          June 4, 2017          FreeBSD 13.1-RELEASE-p6