tsearch(3) — Linux manual page


tsearch(3)              Library Functions Manual              tsearch(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

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 *restrict key, void **restrict 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

       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

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

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

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            │

STANDARDS         top



HISTORY         top

              POSIX.1-2001, POSIX.1-2008, SVr4.

              glibc 2.30.

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 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         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 <stddef.h>
       #include <stdio.h>
       #include <stdlib.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");

       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  *ptr;
           int  **val;

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       This page was obtained from the tarball man-pages-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

Linux man-pages 6.9.1          2024-06-15                     tsearch(3)

Pages that refer to this page: bsearch(3)hsearch(3)lsearch(3)