# tsearch

## NAME



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


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#include <search.h>**
    
           **typedef enum { preorder, postorder, endorder, leaf } VISIT;**
    
           **void *tfind(const void ***_key_**, void *const ***_rootp_**,**
                       **typeof(int (const void *, const void *)) ***_compar_**);**
           **void *tsearch(const void ***_key_**, void ****_rootp_**,**
                       **typeof(int (const void *, const void *)) ***_compar_**);**
           **void *tdelete(const void *restrict** _key_**, void **restrict** _rootp_**,**
                       **typeof(int (const void *, const void *)) ***_compar_**);**
           **void twalk(const void ***_root_**,**
                       **typeof(void (const void ***_nodep_**, VISIT** _which_**, int** _depth_**))**
                           *****_action_**);**
    
           **#define _GNU_SOURCE** /* See feature_test_macros(7) */
           **#include <search.h>**
    
           **void twalk_r(const void ***_root_**,**
                       **typeof(void (const void ***_nodep_**, VISIT** _which_**, void ***_closure_**))**
                           *****_action_**,**
                       **void ***_closure_**);**
           **void tdestroy(void ***_root_**,**
                       **typeof(void (void ***_nodep_**)) ***_free_node_**);**
    


## 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.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌───────────────────────────┬───────────────┬────────────────────┐
           │ **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



           **tsearch**()
           **tfind**()
           **tdelete**()
           **twalk**()
                  POSIX.1-2008.
    
           **tdestroy**()
           **twalk_r**()
                  GNU.
    


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


* * *