NAME
tdelete, tfind, tsearch, twalk - manage a binary search tree
SYNOPSIS
#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
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 a null pointer if the node is not found.
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.
RETURN VALUE
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 a null pointer if the node is not found.
The twalk() function shall not return a value.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
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
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
hcreate() , lsearch() , the Base Definitions volume of
IEEE Std 1003.1-2001, <search.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .