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. 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 <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         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 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 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.1‐2008, search.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                         TDELETE(3P)

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