TSEARCH(3C) (C Programming Language Utilities) TSEARCH(3C)
NAME
tsearch, tfind, tdelete, twalk - manage binary search trees
SYNOPSIS
#include <search.h>
char *tsearch ((char *) key, (char **) rootp, compar)
int (*compar)( );
char *tfind ((char *) key, (char **) rootp, compar)
int (*compar)( );
char *tdelete ((char *) key, (char **) rootp, compar)
int (*compar)( );
void twalk ((char *) root, action)
void (*action)( );
DESCRIPTION
tsearch, tfind, tdelete, and twalk 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 routine. This routine is called with
two arguments, the pointers to the 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.
tsearch is used to build and access the tree. Key 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 routine must store the
data. Rootp 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
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set to point to the datum which will be at the root of the
new tree.
Like tsearch, tfind will search for a datum in the tree,
returning a pointer to it if found. However, if it is not
found, tfind will return a NULL pointer. The arguments for
tfind are the same as for tsearch.
Tdelete 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. Tdelete returns a pointer to the parent of the
deleted node, or a NULL pointer if the node is not found.
Twalk traverses a binary search tree. Root 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.) 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 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.
EXAMPLE
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.
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TSEARCH(3C) (C Programming Language Utilities) TSEARCH(3C)
#include <search.h>
#include <stdio.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 routine 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,
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((struct node *) node2)->string);
}
/*
This routine prints out a node, the first time
twalk encounters it.
*/
void
print_node(node, order, level)
char **node;
VISIT order;
int level;
{
if (order == preorder || order == leaf) {
(void)printf("string = %20s, length = %d\n",
(*((struct node **)node))->string,
(*((struct node **)node))->length);
}
}
SEE ALSO
bsearch(3C), hsearch(3C), lsearch(3C).
DIAGNOSTICS
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.
WARNINGS
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. tsearch uses preorder,
postorder and endorder to respectively refer to visting 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
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to refer to the same visits, which could result in some
confusion over the meaning of postorder.
CAVEAT
If the calling function alters the pointer to the root,
results are unpredictable.
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