NAME
tsearch, tfind, tdelete, twalk - manage a binary tree
SYNOPSIS
#include <search.h>
void *tsearch (const void *key, void **rootp,
int (*compar))(const void *, const void *));
void *tfind (const void *key, const void **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 *nodep
const VISIT which,
const int depth)));
DESCRIPTION
tsearch, tfind, twalk, and tdelete manage a binary tree.
They are generalized from Knuth (6.2.2) Algorithm T. The
first field in each node of the tree is a pointer to the
corresponding data item. (The calling program must store
the actual data.) compar points to a comparison routine,
which takes pointers to two items. It should return an
integer which is negative, zero, or positive, depending on
whether the first item is less than, equal to, or greater
than the second.
tsearch searches the tree for an item. key points to the
item to be searched for. rootp points to a variable which
points to the root of the tree. If the tree is empty, then
the variable that rootp points to should be set to NULL. If
the item is found in the tree, then tsearch returns a
pointer to it. If it is not found, then tsearch adds it,
and returns a pointer to the newly added item.
tfind is like tsearch, except that if the item is not found,
then tfind returns NULL.
tdelete deletes an item from the tree. Its arguments are
the same as for tsearch.
twalk performs depth-first, left-to-right traversal of a
binary tree. root points to the starting node for the
traversal. If that node is not the root, then only part of
the tree will be visited. twalk calls the user function
action each time a node is visited (that is, three times for
an internal node, and once for a leaf). action, in turn,
takes three arguments. The first is a pointer to the node
being visited. The second is an integer which takes on the
values preorder, postorder, and endorder depending on
whether this is the first, second, or third visit to the
internal node, or leaf if it is the single visit to a leaf
node. (These symbols are defined in <search.h>.) The third
argument is the depth of the node, with zero being the root.
RETURN VALUE
tsearch returns a pointer to a matching item in the tree, or
to the newly added item, or NULL if there was insufficient
memory to add the item. tfind returns a pointer to the
item, or NULL if no match is found. If there are multiple
elements that match the key, the element returned is
unspecified.
tdelete returns a pointer to the parent of the item deleted,
or NULL if the item was not found.
tsearch, tfind, and tdelete also return NULL if rootp was
NULL on entry.
WARNINGS
twalk takes a pointer to the root, while the other functions
take a pointer to a variable which points to the root.
twalk uses postorder to mean "after the left subtree, but
before the right subtree". Some authorities would call this
"inorder", and reserve "postorder" to mean "after both sub-
trees".
tdelete frees the memory required for the node in the tree.
The user is responsible for freeing the memory for the
corresponding data.
The example program depends on the fact that twalk makes no
further reference to a node after calling the user function
with argument "endorder" or "leaf". This works with the GNU
library implementation, but is not in the SysV documenta-
tion.
EXAMPLE
The following program inserts twelve random numbers into a
binary tree, then prints the numbers in order. The numbers
are removed from the tree and their storage freed during the
traversal.
#include <search.h>
#include <stdlib.h>
#include <stdio.h>
void *root=NULL;
void *xmalloc(unsigned n)
{
void *p;
p = malloc(n);
if(p) return p;
fprintf(stderr, "insufficient memory\n");
exit(1);
}
int compare(const void *pa, const void *pb)
{
if(*(int *)pa < *(int *)pb) return -1;
if(*(int *)pa > *(int *)pb) return 1;
return 0;
}
void action(const void *nodep, const VISIT which, const int depth)
{
int *datap;
void *val;
switch(which)
{
case preorder:
break;
case postorder:
datap = *(int **)nodep;
printf("%6d\n", *datap);
break;
case endorder:
datap = *(int **)nodep;
(void)tdelete(datap, &root, compare);
free(datap);
break;
case leaf:
datap = *(int **)nodep;
printf("%6d\n", *datap);
val = tdelete(datap, &root, compare);
free(datap);
break;
}
return;
}
int main()
{
int i, *ptr;
void *val;
for (i = 0; i < 12; i++)
{
ptr = (int *)xmalloc(sizeof(int));
*ptr = rand()&0xff;
val = tsearch((void *)ptr, &root, compare);
if(val == NULL) exit(1);
}
twalk(root, action);
return 0;
}
CONFORMING TO
SVID
SEE ALSO
qsort(3), bsearch(3), hsearch(3),