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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TDELETE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" tdelete 
.SH NAME
tdelete, tfind, tsearch, twalk \- manage a binary search tree
.SH SYNOPSIS
.LP
\fB#include <search.h>
.br
.sp
void *tdelete(const void *restrict\fP \fIkey\fP\fB, void **restrict\fP
\fIrootp\fP\fB,
.br
\ \ \ \ \ \  int(*\fP\fIcompar\fP\fB)(const void *, const void *));
.br
void *tfind(const void *\fP\fIkey\fP\fB, void *const *\fP\fIrootp\fP\fB,
.br
\ \ \ \ \ \  int(*\fP\fIcompar\fP\fB)(const void *, const void *));
.br
void *tsearch(const void *\fP\fIkey\fP\fB, void **\fP\fIrootp\fP\fB,
.br
\ \ \ \ \ \  int (*\fP\fIcompar\fP\fB)(const void *, const void *));
.br
void twalk(const void *\fP\fIroot\fP\fB,
.br
\ \ \ \ \ \  void (*\fP\fIaction\fP\fB)(const void *, VISIT, int));
\fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fItdelete\fP(), \fItfind\fP(), \fItsearch\fP(), and \fItwalk\fP()
functions manipulate binary search trees. Comparisons
are made with a user-supplied routine, the address of which is passed
as the \fIcompar\fP argument. This routine is called with
two arguments, which are the pointers to the elements being compared.
The application shall ensure that the user-supplied routine
returns an integer less than, equal to, or greater than 0, according
to whether the first argument is to be considered 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.
.LP
The \fItsearch\fP() function shall build and access the tree. The
\fIkey\fP argument is a pointer to an element to be accessed
or stored. If there is a node in the tree whose element is equal to
the value pointed to by \fIkey\fP, a pointer to this found
node shall be returned. Otherwise, the value pointed to by \fIkey\fP
shall be inserted (that is, a new node is created and the
value of \fIkey\fP is copied to this node), and a pointer to this
node returned. Only pointers are copied, so the application
shall ensure that the calling routine stores the data. The \fIrootp\fP
argument points to a variable that points to the root node
of the tree. A null pointer value for the variable pointed to by \fIrootp\fP
denotes an empty tree; in this case, the variable
shall be set to point to the node which shall be at the root of the
new tree.
.LP
Like \fItsearch\fP(), \fItfind\fP() shall search for a node in the
tree, returning a pointer to it if found. However, if it is
not found, \fItfind\fP() shall return a null pointer. The arguments
for \fItfind\fP() are the same as for \fItsearch\fP().
.LP
The \fItdelete\fP() function shall delete a node from a binary search
tree. The arguments are the same as for \fItsearch\fP().
The variable pointed to by \fIrootp\fP shall be changed if the deleted
node was the root of the tree. The \fItdelete\fP()
function shall return a pointer to the parent of the deleted node,
or a null pointer if the node is not found.
.LP
The \fItwalk\fP() function shall traverse a binary search tree. The
\fIroot\fP argument is a pointer to the root node of the
tree to be traversed. (Any node in a tree may be used as the root
for a walk below that node.) The argument \fIaction\fP is the
name of a routine to be invoked at each node. This routine is, in
turn, called with three arguments. The first argument shall be
the address of the node being visited. The structure pointed to by
this argument is unspecified and shall not be modified by the
application, but it shall be possible to cast a pointer-to-node into
a pointer-to-pointer-to-element to access the element stored
in the node. The second argument shall be a value from an enumeration
data type:
.sp
.RS
.nf

\fBtypedef enum { preorder, postorder, endorder, leaf } VISIT;
\fP
.fi
.RE
.LP
(defined in \fI<search.h>\fP), depending on whether this is the first,
second, or
third time that the node is visited (during a depth-first, left-to-right
traversal of the tree), or whether the node is a leaf. The
third argument shall be the level of the node in the tree, with the
root being level 0.
.LP
If the calling function alters the pointer to the root, the result
is undefined.
.SH RETURN VALUE
.LP
If the node is found, both \fItsearch\fP() and \fItfind\fP() shall
return a pointer to it. If not, \fItfind\fP() shall return
a null pointer, and \fItsearch\fP() shall return a pointer to the
inserted item.
.LP
A null pointer shall be returned by \fItsearch\fP() if there is not
enough space available to create a new node.
.LP
A null pointer shall be returned by \fItdelete\fP(), \fItfind\fP(),
and \fItsearch\fP() if \fIrootp\fP is a null pointer on
entry.
.LP
The \fItdelete\fP() function shall return a pointer to the parent
of the deleted node, or a null pointer if the node is not
found.
.LP
The \fItwalk\fP() function shall not return a value.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
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 alphabetical order.
.sp
.RS
.nf

\fB#include <search.h>
#include <string.h>
#include <stdio.h>
.sp

#define STRSZ    10000
#define NODSZ    500
.sp

struct node {      /* Pointers to these are stored in the tree. */
    char    *string;
    int     length;
};
.sp

char   string_space[STRSZ];  /* Space to store strings. */
struct node nodes[NODSZ];    /* Nodes to store. */
void  *root = NULL;          /* This points to the root. */
.sp

int main(int argc, char *argv[])
{
    char   *strptr = string_space;
    struct node    *nodeptr = nodes;
    void   print_node(const void *, VISIT, int);
    int    i = 0, node_compare(const void *, const void *);
.sp

    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,
            node_compare);
        /* Adjust pointers, so we do not overwrite tree. */
        strptr += nodeptr->length + 1;
        nodeptr++;
    }
    twalk(root, print_node);
    return 0;
}
.sp

/*
 *  This routine compares two nodes, based on an
 *  alphabetical ordering of the string field.
 */
int
node_compare(const void *node1, const void *node2)
{
    return strcmp(((const struct node *) node1)->string,
        ((const struct node *) node2)->string);
}
.sp

/*
 *  This routine prints out a node, the second time
 *  twalk encounters it or if it is a leaf.
 */
void
print_node(const void *ptr, VISIT order, int level)
{
    const struct node *p = *(const struct node **) ptr;
.sp

    if (order == postorder || order == leaf)  {
        (void) printf("string = %s,  length = %d\\n",
            p->string, p->length);
    }
}
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
The \fIroot\fP argument to \fItwalk\fP() is one level of indirection
less than the \fIrootp\fP arguments to \fItdelete\fP()
and \fItsearch\fP().
.LP
There are two nomenclatures used to refer to the order in which tree
nodes are visited. The \fItsearch\fP() function uses
\fBpreorder\fP, \fBpostorder\fP, and \fBendorder\fP to refer respectively
to visiting a node before any of its children, after
its left child and before its right, and after both its children.
The alternative nomenclature uses \fBpreorder\fP,
\fBinorder\fP, and \fBpostorder\fP to refer to the same visits, which
could result in some confusion over the meaning of
\fBpostorder\fP.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIhcreate\fP() , \fIlsearch\fP() , the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<search.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .