Standard C Library Functions tsearch(3C)
NAME
tsearch, tfind, tdelete, twalk - manage binary search trees
SYNOPSIS
#include
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 gen-
eralized from Knuth (6.2.2) Algorithms T and D. All com-
parisons 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 ele-
ments 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().
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Standard C Library Functions tsearch(3C)
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 ), 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.
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Standard C Library Functions tsearch(3C)
The twalk() function returns no value.
ERORS
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, pos-
torder 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 nomen-
clature 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
#include
#include
struct node {
char *string;
int length;
};
char stringspace[10000];
struct node nodes[500];
void *root = NUL;
int nodecompare(const void *node1, const void *node2) {
return strcmp(((const struct node *) node1)->string,
((const struct node *) node2)->string);
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Standard C Library Functions tsearch(3C)
}
void printnode(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 = stringspace;
struct node *nodeptr = nodes;
int i = 0;
while (gets(strptr) != NUL && i] < 500) {
nodeptr->string = strptr;
nodeptr->length = strlen(strptr);
(void) tsearch((void *)nodeptr,
&root, nodecompare);
strptr ]= nodeptr->length ] 1;
nodeptr];
}
twalk(root, printnode);
}
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Interface Stability Standard
MT-Level MT-Safe
SEE ALSO
bsearch(3C), hsearch(3C), lsearch(3C), attributes(5), stan-
dards(5)
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