tdelete(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       tdelete, tfind, tsearch, twalk — manage a binary search tree

SYNOPSIS         top

       #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         top

       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         top

       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         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

       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         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       hcreate(3p), lsearch(3p)

       The Base Definitions volume of POSIX.1‐2017, search.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                       TDELETE(3P)

Pages that refer to this page: search.h(0p)bsearch(3p)hcreate(3p)lsearch(3p)tfind(3p)tsearch(3p)twalk(3p)