man/man3/Tcl_StandardChannels.3 - toolchains/skids - Git at Google

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 '\" Copyright (c) 2001 by ActiveState Corporation
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 '\" RCS: @(#) $Id: StdChannels.3,v 1.3 2003/01/21 19:39:59 hunt Exp $
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 '\" The definitions below are for supplemental macros used in Tcl/Tk
 '\" manual entries.
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 .TH "Standard Channels" 3 7.5 Tcl "Tcl Library Procedures"
 .BS
 '\" Note:  do not modify the .SH NAME line immediately below!
 .SH NAME
 Tcl_StandardChannels \- How the Tcl library deals with the standard channels

 .SH DESCRIPTION
 .PP
 This page explains the initialization and use of standard channels in
 the Tcl library.
 .PP
 The term \fIstandard channels\fR comes out of the Unix world and
 refers to the three channels automatically opened by the OS for
 each new application. They are \fBstdin\fR, \fBstdout\fR and
 \fBstderr\fR. The first is the standard input an application can read
 from, the other two refer to writable channels, one for regular
 output and the other for error messages.
 .PP
 Tcl generalizes this concept in a cross-platform way and
 exposes standard channels to the script level.

 .SH APIs
 .PP
 The public API procedures dealing directly with standard channels are
 \fBTcl_GetStdChannel\fR and \fBTcl_SetStdChannel\fR. Additional public
 APIs to consider are \fBTcl_RegisterChannel\fR,
 \fBTcl_CreateChannel\fR and \fBTcl_GetChannel\fR.
 .SH "INITIALIZATION OF TCL STANDARD CHANNELS"
 .PP
 Standard channels are initialized by the Tcl library in three cases:
 when explicitly requested, when implicitly required before returning
 channel information, or when implicitly required during registration
 of a new channel.
 .PP
 These cases differ in how they handle unavailable platform- specific
 standard channels.  (A channel is not ``available'' if it could not be
 successfully opened; for example, in a Tcl application run as a
 Windows NT service.)
 .TP
 1)
 A single standard channel is initialized when it is explicitly
 specified in a call to \fBTcl_SetStdChannel\fR.  The state of the
 other standard channels are unaffected.
 .sp
 Missing platform-specific standard channels do not matter here. This
 approach is not available at the script level.
 .TP
 2)
 All uninitialized standard channels are initialized to
 platform-specific default values:
 .RS
 .TP
 (a)
 when open channels are listed with \fBTcl_GetChannelNames\fR (or the
 \fBfile channels\fR script command), or
 .TP
 (b)
 when information about any standard channel is requested with a call
 to \fBTcl_GetStdChannel\fR, or with a call to \fBTcl_GetChannel\fR
 which specifies one of the standard names (\fBstdin\fR, \fBstdout\fR
 and \fBstderr\fR).
 .RE
 .sp
 .RS
 In case of missing platform-specific standard channels, the Tcl
 standard channels are considered as initialized and then immediately
 closed. This means that the first three Tcl channels then opened by
 the application are designated as the Tcl standard channels.
 .RE
 .TP
 3)
 All uninitialized standard channels are initialized to
 platform-specific default values when a user-requested channel is
 registered with \fBTcl_RegisterChannel\fR.
 .sp
 In case of unavailable platform-specific standard channels the channel
 whose creation caused the initialization of the Tcl standard channels
 is made a normal channel.  The next three Tcl channels opened by the
 application are designated as the Tcl standard channels.  In other
 words, of the first four Tcl channels opened by the application the
 second to fourth are designated as the Tcl standard channels.
 .PP
 .SH "RE-INITIALIZATION OF TCL STANDARD CHANNELS"
 .PP
 Once a Tcl standard channel is initialized through one of the methods
 above, closing this Tcl standard channel will cause the next call to
 \fBTcl_CreateChannel\fR to make the new channel the new standard
 channel, too. If more than one Tcl standard channel was closed
 \fBTcl_CreateChannel\fR will fill the empty slots in the order
 \fBstdin\fR, \fBstdout\fR and \fBstderr\fR.
 .PP
 \fBTcl_CreateChannel\fR will not try to reinitialize an empty slot if
 that slot was not initialized before. It is this behavior which
 enables an application to employ method 1 of initialization, i.e. to
 create and designate their own Tcl standard channels.

 .SH tclsh
 .PP
 The Tcl shell (or rather \fBTcl_Main\fR) uses method 2 to initialize
 the standard channels.

 .SH wish
 .PP
 The windowing shell (or rather \fBTk_MainEx\fR) uses method 1 to
 initialize the standard channels (See \fBTk_InitConsoleChannels\fR)
 on non-Unix platforms.  On Unix platforms, \fBTk_MainEx\fR implicitly
 uses method 2 to initialize the standard channels.

 .SH "SEE ALSO"
 Tcl_CreateChannel(3), Tcl_RegisterChannel(3), Tcl_GetChannel(3), Tcl_GetStdChannel(3), Tcl_SetStdChannel(3), Tk_InitConsoleChannels(3), tclsh(1), wish(1), Tcl_Main(3), Tk_MainEx(3)

 .SH KEYWORDS
 standard channels
	'\"
	'\" Copyright (c) 2001 by ActiveState Corporation
	'\"
	'\" See the file "license.terms" for information on usage and redistribution
	'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
	'\"
	'\" RCS: @(#) $Id: StdChannels.3,v 1.3 2003/01/21 19:39:59 hunt Exp $
	'\"
	'\" The 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.
	'\"
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	'\" End of box enclosure.
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	'\" Begin code excerpt.
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	'\" 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
	'\" Start of list of standard options for a Tk widget. The
	'\" options follow on successive lines, in four 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.
	'\"
	'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
	'\"
	'\" # 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 \{\
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	.nr )C \\n()Bu+\\w'(in/out)'u+2n
	..
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	..
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	.LP
	See the \\fBoptions\\fR manual entry for details on the standard options.
	..
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	.LP
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	Command-Line Name: \\fB\\$1\\fR
	Database Name: \\fB\\$2\\fR
	Database Class: \\fB\\$3\\fR
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	..
	.TH "Standard Channels" 3 7.5 Tcl "Tcl Library Procedures"
	.BS
	'\" Note: do not modify the .SH NAME line immediately below!
	.SH NAME
	Tcl_StandardChannels \- How the Tcl library deals with the standard channels

	.SH DESCRIPTION
	.PP
	This page explains the initialization and use of standard channels in
	the Tcl library.
	.PP
	The term \fIstandard channels\fR comes out of the Unix world and
	refers to the three channels automatically opened by the OS for
	each new application. They are \fBstdin\fR, \fBstdout\fR and
	\fBstderr\fR. The first is the standard input an application can read
	from, the other two refer to writable channels, one for regular
	output and the other for error messages.
	.PP
	Tcl generalizes this concept in a cross-platform way and
	exposes standard channels to the script level.

	.SH APIs
	.PP
	The public API procedures dealing directly with standard channels are
	\fBTcl_GetStdChannel\fR and \fBTcl_SetStdChannel\fR. Additional public
	APIs to consider are \fBTcl_RegisterChannel\fR,
	\fBTcl_CreateChannel\fR and \fBTcl_GetChannel\fR.
	.SH "INITIALIZATION OF TCL STANDARD CHANNELS"
	.PP
	Standard channels are initialized by the Tcl library in three cases:
	when explicitly requested, when implicitly required before returning
	channel information, or when implicitly required during registration
	of a new channel.
	.PP
	These cases differ in how they handle unavailable platform- specific
	standard channels. (A channel is not ``available'' if it could not be
	successfully opened; for example, in a Tcl application run as a
	Windows NT service.)
	.TP
	1)
	A single standard channel is initialized when it is explicitly
	specified in a call to \fBTcl_SetStdChannel\fR. The state of the
	other standard channels are unaffected.
	.sp
	Missing platform-specific standard channels do not matter here. This
	approach is not available at the script level.
	.TP
	2)
	All uninitialized standard channels are initialized to
	platform-specific default values:
	.RS
	.TP
	(a)
	when open channels are listed with \fBTcl_GetChannelNames\fR (or the
	\fBfile channels\fR script command), or
	.TP
	(b)
	when information about any standard channel is requested with a call
	to \fBTcl_GetStdChannel\fR, or with a call to \fBTcl_GetChannel\fR
	which specifies one of the standard names (\fBstdin\fR, \fBstdout\fR
	and \fBstderr\fR).
	.RE
	.sp
	.RS
	In case of missing platform-specific standard channels, the Tcl
	standard channels are considered as initialized and then immediately
	closed. This means that the first three Tcl channels then opened by
	the application are designated as the Tcl standard channels.
	.RE
	.TP
	3)
	All uninitialized standard channels are initialized to
	platform-specific default values when a user-requested channel is
	registered with \fBTcl_RegisterChannel\fR.
	.sp
	In case of unavailable platform-specific standard channels the channel
	whose creation caused the initialization of the Tcl standard channels
	is made a normal channel. The next three Tcl channels opened by the
	application are designated as the Tcl standard channels. In other
	words, of the first four Tcl channels opened by the application the
	second to fourth are designated as the Tcl standard channels.
	.PP
	.SH "RE-INITIALIZATION OF TCL STANDARD CHANNELS"
	.PP
	Once a Tcl standard channel is initialized through one of the methods
	above, closing this Tcl standard channel will cause the next call to
	\fBTcl_CreateChannel\fR to make the new channel the new standard
	channel, too. If more than one Tcl standard channel was closed
	\fBTcl_CreateChannel\fR will fill the empty slots in the order
	\fBstdin\fR, \fBstdout\fR and \fBstderr\fR.
	.PP
	\fBTcl_CreateChannel\fR will not try to reinitialize an empty slot if
	that slot was not initialized before. It is this behavior which
	enables an application to employ method 1 of initialization, i.e. to
	create and designate their own Tcl standard channels.

	.SH tclsh
	.PP
	The Tcl shell (or rather \fBTcl_Main\fR) uses method 2 to initialize
	the standard channels.

	.SH wish
	.PP
	The windowing shell (or rather \fBTk_MainEx\fR) uses method 1 to
	initialize the standard channels (See \fBTk_InitConsoleChannels\fR)
	on non-Unix platforms. On Unix platforms, \fBTk_MainEx\fR implicitly
	uses method 2 to initialize the standard channels.

	.SH "SEE ALSO"
	Tcl_CreateChannel(3), Tcl_RegisterChannel(3), Tcl_GetChannel(3), Tcl_GetStdChannel(3), Tcl_SetStdChannel(3), Tk_InitConsoleChannels(3), tclsh(1), wish(1), Tcl_Main(3), Tk_MainEx(3)

	.SH KEYWORDS
	standard channels