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TDELETE(3P)                POSIX Programmer's Manual               TDELETE(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       tdelete, tfind, tsearch, twalk - manage a binary search tree
SYNOPSIS
       #include <search.h>
       void *tdelete(const void *restrict key, void **restrict rootp,
              int(*compar)(const void *, const void *));
       void *tfind(const void *key, void *const *rootp,
              int(*compar)(const void *, const void *));
       void *tsearch(const void *key, void **rootp,
              int (*compar)(const void *, const void *));
       void twalk(const void *root,
              void (*action)(const void *, VISIT, int));

DESCRIPTION
       The tdelete(), tfind(), tsearch(),  and  twalk()  functions  manipulate
       binary search trees. Comparisons are made with a user-supplied routine,
       the address of which is passed as the compar argument. This routine  is
       called with two arguments, which are the pointers to the elements being
       compared.  The application shall ensure that the user-supplied  routine
       returns an integer less than, equal to, or greater than 0, according to
       whether the first argument is to be considered less than, equal to,  or
       greater than the second argument. The comparison function need not com-
       pare every byte, so arbitrary data may be contained in the elements  in
       addition to the values being compared.
       The  tsearch()  function shall build and access the tree. The key argu-
       ment is a pointer to an element to be accessed or stored. If there is a
       node in the tree whose element is equal to the value pointed to by key,
       a pointer to this found node shall be returned.  Otherwise,  the  value
       pointed to by key shall be inserted (that is, a new node is created and
       the value of key is copied to this node), and a pointer  to  this  node
       returned.  Only  pointers  are  copied, so the application shall ensure
       that the calling routine stores the data. The rootp argument points  to
       a  variable  that  points  to the root node of the tree. A null pointer
       value for the variable pointed to by rootp denotes an  empty  tree;  in
       this  case,  the variable shall be set to point to the node which shall
       be at the root of the new tree.
       Like tsearch(), tfind() shall search for a node in the tree,  returning
       a  pointer  to  it if found. However, if it is not found, tfind() shall
       return a null pointer. The arguments for tfind() are the  same  as  for
       tsearch().
       The  tdelete()  function shall delete a node from a binary search tree.
       The arguments are the same as for tsearch().  The variable  pointed  to
       by rootp shall be changed if the deleted node was the root of the tree.
       The tdelete() function shall return a pointer  to  the  parent  of  the
       deleted node, or a null pointer if the node is not found.
       The  twalk()  function  shall  traverse  a binary search tree. The root
       argument is a pointer to the root node of the  tree  to  be  traversed.
       (Any  node  in  a  tree  may  be used as the root for a walk below that
       node.) The argument action is the name of a routine to  be  invoked  at
       each  node.  This routine is, in turn, called with three arguments. The
       first argument shall be the address of  the  node  being  visited.  The
       structure  pointed  to by this argument is unspecified and shall not be
       modified by the application,  but  it  shall  be  possible  to  cast  a
       pointer-to-node into a pointer-to-pointer-to-element to access the ele-
       ment stored in the node. The second argument shall be a value  from  an
       enumeration data type:

              typedef enum { preorder, postorder, endorder, leaf } VISIT;
       (defined  in  <search.h>), depending on whether this is the first, sec-
       ond, or third time that the node  is  visited  (during  a  depth-first,
       left-to-right  traversal  of  the tree), or whether the node is a leaf.
       The third argument shall be the level of the node in the tree, with the
       root being level 0.
       If  the  calling function alters the pointer to the root, the result is
       undefined.
RETURN VALUE
       If the node is found, both tsearch() and tfind() shall return a pointer
       to it. If not, tfind() shall return a null pointer, and tsearch() shall
       return a pointer to the inserted item.
       A null pointer shall be returned by tsearch() if there  is  not  enough
       space available to create a new node.
       A  null  pointer shall be returned by tdelete(), tfind(), and tsearch()
       if rootp is a null pointer on entry.
       The tdelete() function shall return a pointer  to  the  parent  of  the
       deleted node, or a null pointer if the node is not found.
       The twalk() function shall not return a value.
ERRORS
       No errors are defined.
       The following sections are informative.
EXAMPLES
       The  following code reads in strings and stores structures containing a
       pointer to each string and a count of its length.  It  then  walks  the
       tree, printing out the stored strings and their lengths in alphabetical
       order.

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

              #define STRSZ    10000
              #define NODSZ    500

              struct node {      /* Pointers to these are stored in the tree. */
                  char    *string;
                  int     length;
              };

              char   string_space[STRSZ];  /* Space to store strings. */
              struct node nodes[NODSZ];    /* Nodes to store. */
              void  *root = NULL;          /* This points to the root. */

              int main(int argc, char *argv[])
              {
                  char   *strptr = string_space;
                  struct node    *nodeptr = nodes;
                  void   print_node(const void *, VISIT, int);
                  int    i = 0, node_compare(const void *, const void *);

                  while (gets(strptr) != NULL && i++ < NODSZ)  {
                      /* Set node. */
                      nodeptr->string = strptr;
                      nodeptr->length = strlen(strptr);
                      /* Put node into the tree. */
                      (void) tsearch((void *)nodeptr, (void **)&root,
                          node_compare);
                      /* Adjust pointers, so we do not overwrite tree. */
                      strptr += nodeptr->length + 1;
                      nodeptr++;
                  }
                  twalk(root, print_node);
                  return 0;
              }

              /*
               *  This routine compares two nodes, based on an
               *  alphabetical ordering of the string field.
               */
              int
              node_compare(const void *node1, const void *node2)
              {
                  return strcmp(((const struct node *) node1)->string,
                      ((const struct node *) node2)->string);
              }

              /*
               *  This routine prints out a node, the second time
               *  twalk encounters it or if it is a leaf.
               */
              void
              print_node(const void *ptr, VISIT order, int level)
              {
                  const struct node *p = *(const struct node **) ptr;

                  if (order == postorder || order == leaf)  {
                      (void) printf("string = %s,  length = %d\n",
                          p->string, p->length);
                  }
              }
APPLICATION USAGE
       The root argument to twalk() is one level of indirection less than  the
       rootp arguments to tdelete() and tsearch().
       There  are  two  nomenclatures used to refer to the order in which tree
       nodes are visited. The tsearch() function uses preorder, postorder, and
       endorder  to  refer  respectively  to visiting a node before any of its
       children, after its left child and before its right, and after both its
       children.   The  alternative  nomenclature  uses preorder, inorder, and
       postorder to refer to the same visits, which could result in some  con-
       fusion over the meaning of postorder.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       hcreate(),     lsearch(),    the    Base    Definitions    volume    of
       IEEE Std 1003.1-2001, <search.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the  referee document. The original Standard can be obtained online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                          TDELETE(3P)