tfind(3) — Linux manual page


TSEARCH(3)                Linux Programmer's Manual               TSEARCH(3)

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       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         top

       twalk_r() is available in glibc since version 2.30.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface           Attribute     Value              │
       │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         top

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

NOTES         top

       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

       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         top

       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 <stdlib.h>
       #include <stdio.h>
       #include <time.h>

       static void *root = NULL;

       static void *
       xmalloc(unsigned n)
           void *p;
           p = malloc(n);
           if (p)
               return p;
           fprintf(stderr, "insufficient memory\n");

       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:
           case postorder:
               datap = *(int **) nodep;
               printf("%6d\n", *datap);
           case endorder:
           case leaf:
               datap = *(int **) nodep;
               printf("%6d\n", *datap);

           int i, *ptr;
           void *val;

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

SEE ALSO         top

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

COLOPHON         top

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GNU                              2020-06-09                       TSEARCH(3)