jammy (3) tsearch.3.gz

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NAME

       tsearch, tfind, tdelete, twalk, tdestroy - manage a binary search tree

SYNOPSIS

       #include <search.h>

       typedef enum { preorder, postorder, endorder, leaf } VISIT;

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

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

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

       void twalk(const void *root,
                       void (*action)(const void *nodep, VISIT which,
                                      int depth));

       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <search.h>

       void twalk_r(const void *root,
                       void (*action)(const void *nodep, VISIT which,
                                      void *closure),
                       void *closure);

       void tdestroy(void *root, void (*free_node)(void *nodep));

DESCRIPTION

       tsearch(),  tfind(), twalk(), and tdelete() manage a binary search tree.  They are generalized from Knuth
       (6.2.2) Algorithm T.  The first field in each node of the tree is a pointer  to  the  corresponding  data
       item.   (The  calling  program must store the actual data.)  compar points to a comparison routine, which
       takes pointers to two items.  It should return an integer which is negative, zero, or positive, depending
       on whether the first item is less than, equal to, or greater than the second.

       tsearch()  searches  the tree for an item.  key points to the item to be searched for.  rootp points to a
       variable which points to the root of the tree.  If the tree is empty, then the variable that rootp points
       to  should  be  set  to  NULL.  If the item is found in the tree, then tsearch() returns a pointer to the
       corresponding tree node.  (In other words, tsearch() returns a pointer to a pointer to  the  data  item.)
       If the item is not found, then tsearch() adds it, and returns a pointer to the corresponding tree node.

       tfind() is like tsearch(), except that if the item is not found, then tfind() returns NULL.

       tdelete() deletes an item from the tree.  Its arguments are the same as for tsearch().

       twalk() performs depth-first, left-to-right traversal of a binary tree.  root points to the starting node
       for the traversal.  If that node is not the root, then only part of the tree will  be  visited.   twalk()
       calls  the  user  function action each time a node is visited (that is, three times for an internal node,
       and once for a leaf).  action, in turn, takes three arguments.  The first argument is a  pointer  to  the
       node  being visited.  The structure of the node is unspecified, but it is possible to cast the pointer to
       a pointer-to-pointer-to-element in order to access the element stored within the node.   The  application
       must not modify the structure pointed to by this argument.  The second argument is an integer which takes
       one of the values preorder, postorder, or endorder depending on whether this is  the  first,  second,  or
       third  visit  to the internal node, or the value leaf if this is the single visit to a leaf node.  (These
       symbols are defined in <search.h>.)  The third argument is the depth of the node; the root node has depth
       zero.

       (More  commonly,  preorder, postorder, and endorder are known as preorder, inorder, and postorder: before
       visiting the children, after the first and before the second, and after visiting the children.  Thus, the
       choice of name postorder is rather confusing.)

       twalk_r()  is  similar  to  twalk(),  but  instead of the depth argument, the closure argument pointer is
       passed to each invocation of  the  action  callback,  unchanged.   This  pointer  can  be  used  to  pass
       information  to  and  from  the  callback  function in a thread-safe fashion, without resorting to global
       variables.

       tdestroy() removes the whole tree pointed to by root, freeing all resources allocated  by  the  tsearch()
       function.   For  the data in each tree node the function free_node is called.  The pointer to the data is
       passed as the argument to the function.  If no such work is necessary, free_node must point to a function
       doing nothing.

RETURN VALUE

       tsearch()  returns a pointer to a matching node in the tree, or to the newly added node, or NULL if there
       was insufficient memory to add the item.  tfind() returns a pointer to the node, or NULL if no  match  is
       found.  If there are multiple items that match the key, the item whose node is returned is unspecified.

       tdelete() returns a pointer to the parent of the node deleted, or NULL if the item was not found.  If the
       deleted node was the root node, tdelete() returns a dangling pointer that must not be accessed.

       tsearch(), tfind(), and tdelete() also return NULL if rootp was NULL on entry.

VERSIONS

       twalk_r() is available in glibc since version 2.30.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────┬───────────────┬────────────────────┐
       │InterfaceAttributeValue              │
       ├────────────────────┼───────────────┼────────────────────┤
       │tsearch(), tfind(), │ Thread safety │ MT-Safe race:rootp │
       │tdelete()           │               │                    │
       ├────────────────────┼───────────────┼────────────────────┤
       │twalk()             │ Thread safety │ MT-Safe race:root  │
       ├────────────────────┼───────────────┼────────────────────┤
       │twalk_r()           │ Thread safety │ MT-Safe race:root  │
       ├────────────────────┼───────────────┼────────────────────┤
       │tdestroy()          │ Thread safety │ MT-Safe            │
       └────────────────────┴───────────────┴────────────────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, SVr4.  The functions tdestroy() and twalk_r() are GNU extensions.

NOTES

       twalk() takes a pointer to the root, while the other functions take a pointer to a variable which  points
       to the root.

       tdelete()  frees  the  memory required for the node in the tree.  The user is responsible for freeing the
       memory for the corresponding data.

       The example program depends on the fact that twalk() makes no further reference to a node  after  calling
       the  user  function  with argument "endorder" or "leaf".  This works with the GNU library implementation,
       but is not in the System V documentation.

EXAMPLES

       The following program inserts twelve random numbers into a  binary  tree,  where  duplicate  numbers  are
       collapsed, then prints the numbers in order.

       #define _GNU_SOURCE     /* Expose declaration of tdestroy() */
       #include <search.h>
       #include <stddef.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <time.h>

       static void *root = NULL;

       static void *
       xmalloc(size_t n)
       {
           void *p;
           p = malloc(n);
           if (p)
               return p;
           fprintf(stderr, "insufficient memory\n");
           exit(EXIT_FAILURE);
       }

       static int
       compare(const void *pa, const void *pb)
       {
           if (*(int *) pa < *(int *) pb)
               return -1;
           if (*(int *) pa > *(int *) pb)
               return 1;
           return 0;
       }

       static void
       action(const void *nodep, VISIT which, int depth)
       {
           int *datap;

           switch (which) {
           case preorder:
               break;
           case postorder:
               datap = *(int **) nodep;
               printf("%6d\n", *datap);
               break;
           case endorder:
               break;
           case leaf:
               datap = *(int **) nodep;
               printf("%6d\n", *datap);
               break;
           }
       }

       int
       main(void)
       {
           int **val;

           srand(time(NULL));
           for (int i = 0; i < 12; i++) {
               int *ptr = xmalloc(sizeof(*ptr));
               *ptr = rand() & 0xff;
               val = tsearch(ptr, &root, compare);
               if (val == NULL)
                   exit(EXIT_FAILURE);
               else if (*val != ptr)
                   free(ptr);
           }
           twalk(root, action);
           tdestroy(root, free);
           exit(EXIT_SUCCESS);
       }

SEE ALSO

       bsearch(3), hsearch(3), lsearch(3), qsort(3)

COLOPHON

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