TSEARCH (3)
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 subtrees".
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 documentation.
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
SEE ALSO
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