Tribblix: manual page: tsearch.3c

TSEARCH(3C) Standard C Library Functions TSEARCH(3C)

NAME

tsearch, tfind, tdelete, twalk - manage binary search trees

SYNOPSIS

#include <search.h>

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) (void *, VISIT, int));

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 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.

The tsearch() function is used to build and access the tree. The key
argument 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. The rootp argument 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() 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().

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.
tdelete() 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
argument 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 <search.h>), 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.

RETURN VALUES

If the node is found, both tsearch() and tfind() return a pointer to
it. If not, tfind() returns a null pointer, and tsearch() returns a
pointer to the inserted item.

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 tsearch(), tfind() and tdelete() if
rootp is a null pointer on entry.

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 returns no value.

ERRORS

No errors are defined.

USAGE

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
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 alternate nomenclature uses preorder, inorder and
postorder to refer to the same visits, which could result in some
confusion over the meaning of postorder.

If the calling function alters the pointer to the root, the results
are unpredictable.

These functions safely allows concurrent access by multiple threads
to disjoint data, such as overlapping subtrees or tables.

EXAMPLES

Example 1: A sample program of using tsearch() function.

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 <string.h>
#include <stdio.h>
#include <search.h>
struct node {
char *string;
int length;
};
char string_space[10000];
struct node nodes[500];
void *root = NULL;

int node_compare(const void *node1, const void *node2) {
return strcmp(((const struct node *) node1)->string,
((const struct node *) node2)->string);
}

void print_node(const void *node, VISIT order, int level) {
if (order == preorder || order == leaf) {
printf("length=%d, string=%20s\n",
(*(struct node **)node)->length,
(*(struct node **)node)->string);
}
}

main()
{
char *strptr = string_space;
struct node *nodeptr = nodes;
int i = 0;

while (gets(strptr) != NULL && i++ < 500) {
nodeptr->string = strptr;
nodeptr->length = strlen(strptr);
(void) tsearch((void *)nodeptr,
&root, node_compare);
strptr += nodeptr->length + 1;
nodeptr++;
}
twalk(root, print_node);
}

ATTRIBUTES