TSEARCH(3C)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-sup‐
plied 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
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
├────────────────────┼─────────────────┤
│MT-Level │ MT-Safe │
└────────────────────┴─────────────────┘
SEE ALSObsearch(3C), hsearch(3C), lsearch(3C), attributes(5), standards(5)
Dec 6, 2004 TSEARCH(3C)
