'\"
'\" Copyright (c) 1999-2000 Ajuba Solutions.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
.TH Tcl_StackChannel 3tcl 8.3 Tcl "Tcl Library Procedures"
.\" The -*- nroff -*- definitions below are for supplemental macros used
.\" in Tcl/Tk manual entries.
.\"
.\" .AP type name in/out ?indent?
.\"	Start paragraph describing an argument to a library procedure.
.\"	type is type of argument (int, etc.), in/out is either "in", "out",
.\"	or "in/out" to describe whether procedure reads or modifies arg,
.\"	and indent is equivalent to second arg of .IP (shouldn't ever be
.\"	needed;  use .AS below instead)
.\"
.\" .AS ?type? ?name?
.\"	Give maximum sizes of arguments for setting tab stops.  Type and
.\"	name are examples of largest possible arguments that will be passed
.\"	to .AP later.  If args are omitted, default tab stops are used.
.\"
.\" .BS
.\"	Start box enclosure.  From here until next .BE, everything will be
.\"	enclosed in one large box.
.\"
.\" .BE
.\"	End of box enclosure.
.\"
.\" .CS
.\"	Begin code excerpt.
.\"
.\" .CE
.\"	End code excerpt.
.\"
.\" .VS ?version? ?br?
.\"	Begin vertical sidebar, for use in marking newly-changed parts
.\"	of man pages.  The first argument is ignored and used for recording
.\"	the version when the .VS was added, so that the sidebars can be
.\"	found and removed when they reach a certain age.  If another argument
.\"	is present, then a line break is forced before starting the sidebar.
.\"
.\" .VE
.\"	End of vertical sidebar.
.\"
.\" .DS
.\"	Begin an indented unfilled display.
.\"
.\" .DE
.\"	End of indented unfilled display.
.\"
.\" .SO ?manpage?
.\"	Start of list of standard options for a Tk widget. The manpage
.\"	argument defines where to look up the standard options; if
.\"	omitted, defaults to "options". The options follow on successive
.\"	lines, in three columns separated by tabs.
.\"
.\" .SE
.\"	End of list of standard options for a Tk widget.
.\"
.\" .OP cmdName dbName dbClass
.\"	Start of description of a specific option.  cmdName gives the
.\"	option's name as specified in the class command, dbName gives
.\"	the option's name in the option database, and dbClass gives
.\"	the option's class in the option database.
.\"
.\" .UL arg1 arg2
.\"	Print arg1 underlined, then print arg2 normally.
.\"
.\" .QW arg1 ?arg2?
.\"	Print arg1 in quotes, then arg2 normally (for trailing punctuation).
.\"
.\" .PQ arg1 ?arg2?
.\"	Print an open parenthesis, arg1 in quotes, then arg2 normally
.\"	(for trailing punctuation) and then a closing parenthesis.
.\"
.\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
.ad b
.\"	# Start an argument description
.de AP
.ie !"\\$4"" .TP \\$4
.el \{\
.   ie !"\\$2"" .TP \\n()Cu
.   el          .TP 15
.\}
.ta \\n()Au \\n()Bu
.ie !"\\$3"" \{\
\&\\$1 \\fI\\$2\\fP (\\$3)
.\".b
.\}
.el \{\
.br
.ie !"\\$2"" \{\
\&\\$1	\\fI\\$2\\fP
.\}
.el \{\
\&\\fI\\$1\\fP
.\}
.\}
..
.\"	# define tabbing values for .AP
.de AS
.nr )A 10n
.if !"\\$1"" .nr )A \\w'\\$1'u+3n
.nr )B \\n()Au+15n
.\"
.if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n
.nr )C \\n()Bu+\\w'(in/out)'u+2n
..
.AS Tcl_Interp Tcl_CreateInterp in/out
.\"	# BS - start boxed text
.\"	# ^y = starting y location
.\"	# ^b = 1
.de BS
.br
.mk ^y
.nr ^b 1u
.if n .nf
.if n .ti 0
.if n \l'\\n(.lu\(ul'
.if n .fi
..
.\"	# BE - end boxed text (draw box now)
.de BE
.nf
.ti 0
.mk ^t
.ie n \l'\\n(^lu\(ul'
.el \{\
.\"	Draw four-sided box normally, but don't draw top of
.\"	box if the box started on an earlier page.
.ie !\\n(^b-1 \{\
\h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.el \}\
\h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.\}
.fi
.br
.nr ^b 0
..
.\"	# VS - start vertical sidebar
.\"	# ^Y = starting y location
.\"	# ^v = 1 (for troff;  for nroff this doesn't matter)
.de VS
.if !"\\$2"" .br
.mk ^Y
.ie n 'mc \s12\(br\s0
.el .nr ^v 1u
..
.\"	# VE - end of vertical sidebar
.de VE
.ie n 'mc
.el \{\
.ev 2
.nf
.ti 0
.mk ^t
\h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n'
.sp -1
.fi
.ev
.\}
.nr ^v 0
..
.\"	# Special macro to handle page bottom:  finish off current
.\"	# box/sidebar if in box/sidebar mode, then invoked standard
.\"	# page bottom macro.
.de ^B
.ev 2
'ti 0
'nf
.mk ^t
.if \\n(^b \{\
.\"	Draw three-sided box if this is the box's first page,
.\"	draw two sides but no top otherwise.
.ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.\}
.if \\n(^v \{\
.nr ^x \\n(^tu+1v-\\n(^Yu
\kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c
.\}
.bp
'fi
.ev
.if \\n(^b \{\
.mk ^y
.nr ^b 2
.\}
.if \\n(^v \{\
.mk ^Y
.\}
..
.\"	# DS - begin display
.de DS
.RS
.nf
.sp
..
.\"	# DE - end display
.de DE
.fi
.RE
.sp
..
.\"	# SO - start of list of standard options
.de SO
'ie '\\$1'' .ds So \\fBoptions\\fR
'el .ds So \\fB\\$1\\fR
.SH "STANDARD OPTIONS"
.LP
.nf
.ta 5.5c 11c
.ft B
..
.\"	# SE - end of list of standard options
.de SE
.fi
.ft R
.LP
See the \\*(So manual entry for details on the standard options.
..
.\"	# OP - start of full description for a single option
.de OP
.LP
.nf
.ta 4c
Command-Line Name:	\\fB\\$1\\fR
Database Name:	\\fB\\$2\\fR
Database Class:	\\fB\\$3\\fR
.fi
.IP
..
.\"	# CS - begin code excerpt
.de CS
.RS
.nf
.ta .25i .5i .75i 1i
..
.\"	# CE - end code excerpt
.de CE
.fi
.RE
..
.\"	# UL - underline word
.de UL
\\$1\l'|0\(ul'\\$2
..
.\"	# QW - apply quotation marks to word
.de QW
.ie '\\*(lq'"' ``\\$1''\\$2
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\$2
..
.\"	# PQ - apply parens and quotation marks to word
.de PQ
.ie '\\*(lq'"' (``\\$1''\\$2)\\$3
.\"" fix emacs highlighting
.el (\\*(lq\\$1\\*(rq\\$2)\\$3
..
.\"	# QR - quoted range
.de QR
.ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3
..
.\"	# MT - "empty" string
.de MT
.QW ""
..
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel, Tcl_GetTopChannel \- manipulate stacked I/O channels
.SH SYNOPSIS
.nf
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Channel
\fBTcl_StackChannel\fR(\fIinterp, typePtr, clientData, mask, channel\fR)
.sp
int
\fBTcl_UnstackChannel\fR(\fIinterp, channel\fR)
.sp
Tcl_Channel
\fBTcl_GetStackedChannel\fR(\fIchannel\fR)
.sp
Tcl_Channel
\fBTcl_GetTopChannel\fR(\fIchannel\fR)
.sp
.SH ARGUMENTS
.AS Tcl_ChannelType clientData
.AP Tcl_Interp *interp in
Interpreter for error reporting.
.AP "const Tcl_ChannelType" *typePtr in
The new channel I/O procedures to use for \fIchannel\fR.
.AP void *clientData in
Arbitrary one-word value to pass to channel I/O procedures.
.AP int mask in
Conditions under which \fIchannel\fR will be used: OR-ed combination of
\fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR and \fBTCL_EXCEPTION\fR.
This can be a subset of the operations currently allowed on \fIchannel\fR.
.AP Tcl_Channel channel in
An existing Tcl channel such as returned by \fBTcl_CreateChannel\fR.
.BE

.SH DESCRIPTION
.PP
These functions are for use by extensions that add processing layers to Tcl
I/O channels.  Examples include compression and encryption modules.  These
functions transparently stack and unstack a new channel on top of an
existing one.  Any number of channels can be stacked together.
.PP
The \fBTcl_ChannelType\fR version currently supported is
\fBTCL_CHANNEL_VERSION_5\fR.  See \fBTcl_CreateChannel\fR for details.
.PP
\fBTcl_StackChannel\fR stacks a new \fIchannel\fR on an existing channel
with the same name that was registered for \fIchannel\fR by
\fBTcl_RegisterChannel\fR.
.PP
\fBTcl_StackChannel\fR works by creating a new channel structure and
placing itself on top of the channel stack.  EOL translation, encoding and
buffering options are shared between all channels in the stack.  The hidden
channel does no buffering, newline translations, or character set encoding.
Instead, the buffering, newline translations, and encoding functions all
remain at the top of the channel stack.  A pointer to the new top channel
structure is returned.  If an error occurs when stacking the channel, NULL
is returned instead.
.PP
The \fImask\fR parameter specifies the operations that are allowed on the
new channel.  These can be a subset of the operations allowed on the
original channel.  For example, a read-write channel may become read-only
after the \fBTcl_StackChannel\fR call.
.PP
Closing a channel closes the channels stacked below it.  The close of
stacked channels is executed in a way that allows buffered data to be
properly flushed.
.PP
\fBTcl_UnstackChannel\fR reverses the process.  The old channel is
associated with the channel name, and the processing module added by
\fBTcl_StackChannel\fR is destroyed.  If there is no old channel, then
\fBTcl_UnstackChannel\fR is equivalent to \fBTcl_Close\fR.  If an error
occurs unstacking the channel, \fBTCL_ERROR\fR is returned, otherwise
\fBTCL_OK\fR is returned.
.PP
\fBTcl_GetTopChannel\fR returns the top channel in the stack of
channels the supplied channel is part of.
.PP
\fBTcl_GetStackedChannel\fR returns the channel in the stack of
channels which is just below the supplied channel.

.SH "SEE ALSO"
Notifier(3tcl), Tcl_CreateChannel(3tcl), Tcl_OpenFileChannel(3tcl), vwait(3tcl).

.SH KEYWORDS
channel, compression