.\" $OpenBSD: tsearch.3,v 1.21 2019/01/25 00:19:25 millert Exp $
.\"
.\" Copyright (c) 1997 Todd C. Miller <millert@openbsd.org>
.\"
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.Dd $Mdocdate: January 25 2019 $
.Dt TSEARCH 3
.Os
.Sh NAME
.Nm tsearch ,
.Nm tfind ,
.Nm tdelete ,
.Nm twalk
.Nd manipulate binary search trees
.Sh SYNOPSIS
.In search.h
.Ft void *
.Fn tdelete "const void *key" "void **rootp" "int (*compar)(const void *, const void *)"
.Ft void *
.Fn tfind "const void *key" "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
.Dv 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.
If the node to be deleted is the root of the binary search tree,
.Fa rootp
will be adjusted and an unspecified non-null pointer will be returned.
It takes the same arguments as
.Fn tfind
and
.Fn tsearch .
.Pp
.Fn twalk
walks the binary search tree rooted in
.Fa 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
.Dv NULL
if allocation of a new node fails (usually
due to a lack of free memory).
.Pp
.Fn tdelete
returns a pointer to the parent of the deleted node or an unspecified
non-null pointer if the root node is deleted.
.Pp
.Fn tfind ,
.Fn tsearch ,
and
.Fn tdelete
return
.Dv NULL
if
.Fa rootp
is
.Dv NULL
or the datum cannot be found.
.Sh SEE ALSO
.Xr bsearch 3 ,
.Xr lsearch 3
.Sh STANDARDS
These functions conform to
.St -p1003.1-2008 .
.Sh CAVEATS
The value returned when deleting the root node was unspecified before
the
.St -p1003.1-2008
standard, so users of the
.Fn tdelete
function should be wary of relying on a specific behaviour.