tsearch(3) CLIX tsearch(3)
NAME
tsearch, tfind, tdelete, twalk - Manage binary search trees
LIBRARY
Standard C Library (libc.a)
SYNOPSIS
#include <stdio.h>
#include <search.h>
char *tsearch(
char *key ,
char **rootp ,
int (*compar()) );
char *tfind(
char *key ,
char **rootp ,
int (*compar)() );
char *tdelete(
char *key ,
char **rootp ,
int (**compar)() );
void twalk(
char *root ,
void (*action)() );
PARAMETERS
key Points to a datum.
rootp Points to a variable that points to the root of the tree.
compar Specifies a comparison function.
root Specifies the root of the tree to be traversed.
action Specifies the name of the function to call at each node.
DESCRIPTION
The tsearch(), tfind(), tdelete(), and twalk() functions are routines for
manipulating binary search trees. They are generalized from Knuth (6.2.2)
Algorithms T and D. All comparisons are done with a user-supplied
function. This function is called with two arguments, the pointers to the
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tsearch(3) CLIX tsearch(3)
elements being compared. It 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 is used to build and access the tree. The key
parameter is a pointer to a datum to be accessed or stored. If there is a
datum in the tree equal to *key (the value pointed to by key), a pointer
to this found datum is returned. Otherwise, *key is inserted, and a
pointer to it returned. Only pointers are copied, so the calling function
must store the data. The rootp parameter points to a variable that points
to the root of the tree. A NULL value for the variable pointed to by
rootp denotes an empty tree; in this case, the variable will be set to
point to the datum which will be at the root of the new tree.
Like tsearch(), tfind() searches for a datum in the tree, returning a
pointer to it if found. However, if it is not found, tfind() returns a
NULL pointer. The arguments for tfind() are the same as for tsearch().
The tdelete() function deletes a node from a binary search tree. The
arguments are the same as for tsearch(). The variable pointed to by rootp
will be changed if the deleted node was the root of the tree. The
tdelete() function returns a pointer to the parent of the deleted node, or
a NULL pointer if the node is not found.
The twalk() function traverses a binary search tree. The root parameter
is the root of the tree to be traversed. (Any node in a tree may be used
as the root for a walk below that node.) The action parameter specifies
the name of a function to be invoked at each node. This function is, in
turn, called with three arguments. The first argument is the address of
the node being visited. The second argument is a value from an
enumeration data type typedef enum{ preorder, postorder, endorder, leaf }
VISIT; (defined in the search.h header file), depending on whether this is
the first, second or third time that the node has been visited (during a
depth-first, left-to-right traversal of the tree), or whether the node is
a leaf. The third argument is the level of the node in the tree, with the
root being level zero.
The pointers to the key and the root of the tree should be of type
pointer-to-element, and cast to type pointer-to-character. Similarly,
although declared as type pointer-to-character, the value returned should
be cast into type pointer-to-element.
If the calling function alters the pointer to the root, results are
unpredictable.
EXAMPLES
To read in strings and stores structures containing a pointer to each
string and a count of its length, walk the tree, displaying the stored
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tsearch(3) CLIX tsearch(3)
strings and their lengths in alphabetical order:
#include <stdio.h>
#include <search.h>
struct node { /* pointers to these are stored in the tree */
char *string;
int length;
};
char string_space[10000]; /* space to store strings */
struct node nodes[500]; /* nodes to store */
struct node *root = NULL; /* this points to the root */
main()
{
char *strptr = string_space;
struct node *nodeptr = nodes;
void print_node(), twalk();
int i = 0, node_compare();
while (gets(strptr) != NULL && i++ < 500) {
/* set node */
nodeptr->string = strptr;
nodeptr->length = strlen(strptr);
/* put node into the tree */
(void) tsearch((char *)nodeptr, (char **) &root,
node_compare);
/* adjust pointers, so we don't overwrite tree */
strptr += nodeptr->length + 1;
nodeptr++;
}
twalk((char *)root, print_node);
}
/*
This function compares two nodes, based on an
alphabetical ordering of the string field.
*/
int
node_compare(node1, node2)
char *node1, *node2;
{
return strcmp(((struct node *)node1)->string,
((struct node *) node2)->string);
}
/*
This function displays a node, the first time
twalk encounters it.
*/
void
print_node(node, order, level)
char **node;
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tsearch(3) CLIX tsearch(3)
VISIT order;
int level;
{
if (order == preorder || order == leaf) {
(void)printf("string = %20s, length = %d\n",
(*((struct node **)node))->string,
(*((struct node **)node))->length);
}
}
CAUTIONS
The root argument to twalk() is one level of indirection less than the
rootp arguments to tsearch() and tdelete().
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 respectively refer to visiting a node before any of its children, after
its left child and before its right, and after both its children. The
alternate nomenclature uses preorder, inorder and postorder to refer to
the same visits, which could result in some confusion over the meaning of
postorder.
RETURN VALUES
A NULL pointer is returned by tsearch() if there is not enough space
available to create a new node.
A NULL pointer is returned by tfind() and tdelete() if rootp is NULL on
entry.
If the datum is found, both tsearch() and tfind() return a pointer to it.
If not, tfind() returns NULL, and tsearch() returns a pointer to the
inserted item.
RELATED INFORMATION
Functions: bsearch(3), hsearch(3), lsearch(3)
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