# tdelete

## 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 compare
           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_
           argument 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.  If the deleted node was the root of the tree
           and had no children, the variable pointed to by _rootp_ shall be set
           to a null pointer. The _tdelete_() function shall return a pointer
           to the parent of the deleted node, or an unspecified non-null
           pointer if the deleted node was the root node, or a null pointer
           if the node is not found.
    
           If _tsearch_() adds an element to a tree, or _tdelete_() successfully
           deletes an element from a tree, the concurrent use of that tree in
           another thread, or use of pointers produced by a previous call to
           _tfind_() or _tsearch_(), produces undefined results.
    
           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 element 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,
           second, 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.
    
           If the functions pointed to by _action_ or _compar_ (for any of these
           binary search functions) change the tree, the results are
           undefined.
    
           These functions are thread-safe only as long as multiple threads
           do not access the same tree.
    


## 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 an unspecified non-null pointer if the deleted
           node was the root 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 <limits.h>
               #include <search.h>
               #include <stdlib.h>
               #include <string.h>
               #include <stdio.h>
    
               struct element {      /* Pointers to these are stored in the tree. */
                   int     count;
                   char    string[];
               };
    
               void  *root = NULL;          /* This points to the root. */
    
               int main(void)
               {
                   char   str[_POSIX2_LINE_MAX+1];
                   int    length = 0;
                   struct element *elementptr;
                   void   *node;
                   void   print_node(const void *, VISIT, int);
                   int    node_compare(const void *, const void *),
                          delete_root(const void *, const void *);
    
                   while (fgets(str, sizeof(str), stdin))  {
                       /* Set element. */
                       length = strlen(str);
                       if (str[length-1] == '\n')
                           str[--length] = '\0';
                       elementptr = malloc(sizeof(struct element) + length + 1);
                       strcpy(elementptr->string, str);
                       elementptr->count = 1;
                       /* Put element into the tree. */
                       node = tsearch((void *)elementptr, &root, node_compare);
                       if (node == NULL) {
                           fprintf(stderr,
                                   "tsearch: Not enough space available\n");
                           exit(EXIT_FAILURE);
                       }
                       else if (*(struct element **)node != elementptr) {
                           /* A node containing the element already exists */
                           (*(struct element **)node)->count++;
                           free(elementptr);
                       }
                   }
                   twalk(root, print_node);
    
                   /* Delete all nodes in the tree */
                   while (root != NULL) {
                       elementptr = *(struct element **)root;
                       printf("deleting node: string = %s,  count = %d\n",
                              elementptr->string,
                              elementptr->count);
                       tdelete((void *)elementptr, &root, delete_root);
                       free(elementptr);
                   }
    
                   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 element *) node1)->string,
                       ((const struct element *) node2)->string);
               }
    
               /*
                *  This comparison routine can be used with tdelete()
                *  when explicitly deleting a root node, as no comparison
                *  is necessary.
                */
               int
               delete_root(const void *node1, const void *node2)
               {
                   return 0;
               }
    
               /*
                *  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 element *p = *(const struct element **) ptr;
    
                   if (order == postorder || order == leaf)  {
                       (void) printf("string = %s,  count = %d\n",
                           p->string, p->count);
                   }
               }
    


## 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 _twalk_() 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 confusion over the meaning of
           **postorder**.
    
           Since the return value of _tdelete_() is an unspecified non-null
           pointer in the case that the root of the tree has been deleted,
           applications should only use the return value of _tdelete_() as
           indication of success or failure and should not assume it can be
           dereferenced. Some implementations in this case will return a
           pointer to the new root of the tree (or to an empty tree if the
           deleted root node was the only node in the tree); other
           implementations return arbitrary non-null pointers.
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


* * *