TSEARCH(3) Linux Programmer's Manual TSEARCH(3)
NAME
tsearch, tfind, tdelete, twalk - manage a binary tree
SYNOPSIS
#include<search.h>
void*tsearch(constvoid*key,void**rootp,
int(*compar)(constvoid*,constvoid*));
void*tfind(constvoid*key,constvoid**rootp,
int(*compar)(constvoid*,constvoid*));
void*tdelete(constvoid*key,void**rootp,
int(*compar)(constvoid*,constvoid*));
voidtwalk(constvoid*root,void(*action)(constvoid*nodep,
constVISIT which,
constint depth));
#define_GNU_SOURCE
#include<search.h>
voidtdestroy(void*root,void(*free_node)(void*nodep));
DESCRIPTION
tsearch, tfind, twalk, and tdelete manage a binary tree. They are gen-
eralized 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 inte-
ger 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 vis-
ited. 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.
(More commonly, preorder, postorder, and endorder are known as pre-
order, inorder, and postorder: before visiting the children, after the
first and before the second, and after visiting the children. Thus, the
choice of name postorder is rather confusing.)
tdestroy removes the whole tree pointed to by rootp, freeing all
resources allocated by the tsearch function. For the data in each tree
node the function free_node is called. The pointer to the data is
passed as the argument to the function. If no such work is necessary
free_node must point to a function doing nothing.
RETURNVALUE
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,
where duplicate numbers are collapsed, then prints the numbers in
order.
#include <search.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.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;
switch(which) {
case preorder:
break;
case postorder:
datap = *(int **)nodep;
printf("%6d\n", *datap);
break;
case endorder:
break;
case leaf:
datap = *(int **)nodep;
printf("%6d\n", *datap);
break;
}
}
int main() {
int i, *ptr;
void *val;
srand(time(NULL));
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;
}
CONFORMINGTO
SVID. The function tdestroy() is a GNU extension.
SEEALSO
qsort(3), bsearch(3), hsearch(3), lsearch(3)
GNU 1995-09-24 TSEARCH(3)
Take our 
