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 *key, void **rootp,
int(*compar)(const void *, const void *));
void twalk(const void *root,
void (*action)(const void *, VISIT, int));
DESCRIPTION
tsearch(), tfind(), tdelete(), and twalk() are routines for manipulat-
ing binary search trees. They are generalized from Knuth (6.2.2) Algo-
rithms T and D. All comparisons are done with a user-supplied routine.
This routine is called with two arguments, the pointers to the ele-
ments being compared. It returns an integer less than, equal to, or
greater than 0, according to whether the first argument is to be con-
sidered 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 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.
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tsearch(3C) tsearch(3C)
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 structure
pointed to by this argument is unspecified and must not be modified.
The value of type "pointer-to-node" can be converted to type
"pointer-to-pointer-to-element" to access the elements stored in the
node.
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.
RETURN VALUE
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.
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 alphabeti-
cal order.
#include <search.h>
#include <string.h>
#include <stdio.h>
#define STRSZ 10000
#define NODSZ 500
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tsearch(3C) tsearch(3C)
struct node { /* pointers to these are stored in the tree */
char *string;
int length;
};
char stringspace[STRSZ]; /* space to store strings */
struct node nodes[NODSZ]; /* nodes to store */
void *root = NULL; /* this points to the root */
int main(int argc, char *argv[])
{
char *strptr = stringspace;
struct node *nodeptr = nodes;
void printnode(const void *, VISIT, int);
int i = 0, nodecompare(const void *, const void *);
while (gets(strptr) != NULL && i++ < NODSZ) {
/* set node */
nodeptr->string = strptr;
nodeptr->length = strlen(strptr);
/* put node into the tree */
(void) tsearch((void *)nodeptr, (void **)&root,
nodecompare);
/* adjust pointers, so we do not overwrite tree */
strptr += nodeptr->length + 1;
nodeptr++;
}
twalk(root, printnode);
return 0;
}
/* This routine compares two nodes, based on an
alphabetical ordering of the string field. */
int
nodecompare(const void *node1, const void *node2)
{
return strcmp(((const struct node *) node1)->string,
((const struct node *) node2)->string);
}
/* This routine prints out a node, the second time
twalk encounters it or if it is a leaf. */
void
printnode(const void *ptr, VISIT order, int level)
{
const struct node *p = *(const struct node **) ptr;
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tsearch(3C) tsearch(3C)
if (order == postorder || order == leaf) {
(void) printf("string = %s, length = %d\n",
p->string, p->length);
}
}
RESULT
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.
NOTES
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 chil-
dren. The alternate nomenclature uses preorder, inorder and postorder
to refer to the same visits, so that postorder has a different meaning
in this case.
If the calling function alters the pointer to the root, results are
unpredictable.
SEE ALSO
bsearch(3C), hsearch(3C), lsearch(3C), search(5).
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