.\" $NetBSD: tsearch.3,v 1.12 2010/04/30 10:09:23 jruoho Exp $
.\" Copyright (c) 1997 Todd C. Miller <Todd.Miller@courtesan.com>
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.\"	OpenBSD: tsearch.3,v 1.2 1998/06/21 22:13:49 millert Exp
.\"
.Dd April 30, 2010
.Dt TSEARCH 3
.Os
.Sh NAME
.Nm tsearch, tfind, tdelete, twalk
.Nd manipulate binary search trees
.Sh SYNOPSIS
.In search.h
.Ft void *
.Fn tdelete "const void * restrict key" "void ** restrict rootp" "int (*compar) (const void *, const void *)"
.Ft void *
.Fn tfind "const void *key" "const void * const *rootp" "int (*compar) (const void *, const void *)"
.Ft void *
.Fn tsearch "const void *key" "void **rootp" "int (*compar) (const void *, const void *)"
.Ft void
.Fn twalk "const void *root" "void (*action) (const void *, VISIT, int)"
.Sh DESCRIPTION
The
.Fn tdelete ,
.Fn tfind ,
.Fn tsearch ,
and
.Fn twalk
functions manage binary search trees based on algorithms T and D
from Knuth (6.2.2).
The comparison function passed in by
the user has the same style of return values as
.Xr strcmp 3 .
.Pp
.Fn tfind
searches for the datum matched by the argument
.Fa key
in the binary tree rooted at
.Fa rootp ,
returning a pointer to the datum if it is found and NULL
if it is not.
.Pp
.Fn tsearch
is identical to
.Fn tfind
except that if no match is found,
.Fa key
is inserted into the tree and a pointer to it is returned.
If
.Fa rootp
points to a NULL value a new binary search tree is created.
.Pp
.Fn tdelete
deletes a node from the specified binary search tree and returns
a pointer to the parent of the node to be deleted.
It takes the same arguments as
.Fn tfind
and
.Fn tsearch .
If the node to be deleted is the root of the binary search tree,
.Fa rootp
will be adjusted.
.Pp
.Fn twalk
walks the binary search tree rooted in
.Va root
and calls the function
.Fa action
on each node.
.Fa Action
is called with three arguments: a pointer to the current node,
a value from the enum
.Sy "typedef enum { preorder, postorder, endorder, leaf } VISIT;"
specifying the traversal type, and a node level (where level
zero is the root of the tree).
.Sh RETURN VALUES
The
.Fn tsearch
function returns NULL if allocation of a new node fails (usually
due to a lack of free memory).
.Pp
.Fn tfind ,
.Fn tsearch ,
and
.Fn tdelete
return NULL if
.Fa rootp
is NULL or the datum cannot be found.
.Pp
The
.Fn twalk
function returns no value.
.Sh SEE ALSO
.Xr bsearch 3 ,
.Xr hsearch 3 ,
.Xr lsearch 3
.Sh STANDARDS
These functions conform to
.St -p1003.1-2001 .
.Sh CAVEATS
The
.St -p1003.1-2001
standard does not specify what value should be returned when deleting
the root node.
Since implementations vary, user of
.Fn tdelete
should not rely on any specific behaviour.
The
.St -p1003.1-2008
revision tried to clarify the issue with the following wording:
.Do
the
.Fn tdelete
function shall return a pointer to the parent of the deleted node,
or an unspecified non-NULL pointer if the deleted node was the root node, or a
.Dv NULL
pointer if the node is not found
.Dc .