man-pages/man3/tsearch.3

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.TH TSEARCH 3  2008-09-23 "GNU" "Linux Programmer's Manual"
.SH NAME
tsearch, tfind, tdelete, twalk, tdestroy \- manage a binary tree
.SH SYNOPSIS
.nf
.B #include <search.h>
.sp
.BI "void *tsearch(const void *" key ", void **" rootp ,
.BI "                int (*" compar ")(const void *, const void *));"
.sp
.BI "void *tfind(const void *" key ", const void **" rootp ,
.BI "                int (*" compar ")(const void *, const void *));"
.sp
.BI "void *tdelete(const void *" key ", void **" rootp ,
.BI "                int (*" compar ")(const void *, const void *));"
.sp
.BI "void twalk(const void *" root ", void (*" action ")(const void *" nodep ,
.BI "                                   const VISIT " which ,
.BI "                                   const int " depth "));"
.sp
.B #define _GNU_SOURCE
.br
.B #include <search.h>
.sp
.BI "void tdestroy(void *" root ", void (*" free_node ")(void *" nodep ));
.fi
.SH DESCRIPTION
.BR tsearch (),
.BR tfind (),
.BR twalk (),
and
.BR 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.)
\fIcompar\fP 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.
.PP
.BR tsearch ()
searches the tree for an item.
\fIkey\fP points to the item to be searched for.
\fIrootp\fP points to a variable which points to the root of the tree.
If the tree is empty,
then the variable that \fIrootp\fP points to should be set to NULL.
If the item is found in the tree, then
.BR tsearch ()
returns a pointer
to it.
If it is not found, then
.BR tsearch ()
adds it, and returns a
pointer to the newly added item.
.PP
.BR tfind ()
is like
.BR tsearch (),
except that if the item is not
found, then
.BR tfind ()
returns NULL.
.PP
.BR tdelete ()
deletes an item from the tree.
Its arguments are the same as for
.BR tsearch ().
.PP
.BR twalk ()
performs depth-first, left-to-right traversal of a binary
tree.
\fIroot\fP points to the starting node for the traversal.
If that node is not the root, then only part of the tree will be visited.
.BR twalk ()
calls the user function \fIaction\fP each time a node is
visited (that is, three times for an internal node, and once for a
leaf).
\fIaction\fP, 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 \fBpreorder\fP, \fBpostorder\fP, and
\fBendorder\fP depending on whether this is the first, second, or
third visit to the internal node, or \fBleaf\fP if it is the single
visit to a leaf node.
(These symbols are defined in \fI<search.h>\fP.)
The third argument is the depth of the node, with
zero being the root.
.PP
(More commonly, \fBpreorder\fP, \fBpostorder\fP, and \fBendorder\fP
are known as \fBpreorder\fP, \fBinorder\fP, and \fBpostorder\fP:
before visiting the children, after the first and before the second,
and after visiting the children.
Thus, the choice of name \fBpost\%order\fP
is rather confusing.)
.PP
.BR tdestroy ()
removes the whole tree pointed to by \fIroot\fP,
freeing all resources allocated by the
.BR tsearch ()
function.
For the data in each tree node the function \fIfree_node\fP is called.
The pointer to the data is passed as the argument to the function.
If no such work is necessary \fIfree_node\fP must point to a function
doing nothing.
.SH "RETURN VALUE"
.BR 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.
.BR 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.
.PP
.BR tdelete ()
returns a pointer to the parent of the item deleted, or
NULL if the item was not found.
.PP
.BR tsearch (),
.BR tfind (),
and
.BR tdelete ()
also
return NULL if \fIrootp\fP was NULL on entry.
.SH "CONFORMING TO"
SVr4, POSIX.1-2001.
The function
.BR tdestroy ()
is a GNU extension.
.SH NOTES
.BR twalk ()
takes a pointer to the root, while the other functions
take a pointer to a variable which points to the root.
.PP
.BR twalk ()
uses \fBpostorder\fP 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".
.PP
.BR tdelete ()
frees the memory required for the node in the tree.
The user is responsible for freeing the memory for the corresponding
data.
.PP
The example program depends on the fact that
.BR 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 System V documentation.
.SH EXAMPLE
The following program inserts twelve random numbers into a binary
tree, where duplicate numbers are collapsed, then prints the numbers
in order.
.sp
.nf
#define _GNU_SOURCE     /* Expose declaration of tdestroy() */
#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(EXIT_FAILURE);
}

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(void)
{
    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(EXIT_FAILURE);
        else if ((*(int **) val) != ptr)
            free(ptr);
    }
    twalk(root, action);
    tdestroy(root, free);
    exit(EXIT_SUCCESS);
}
.fi
.SH "SEE ALSO"
.BR bsearch (3),
.BR hsearch (3),
.BR lsearch (3),
.BR qsort (3),
.BR feature_test_macros (7)