Tcl_GetStdChannel(3) Tcl Library Procedures Tcl_GetStdChannel(3)
NAME
Tcl_GetStdChannel, Tcl_SetStdChannel - procedures for retrieving and
replacing the standard channels
SYNOPSIS
#include <tcl.h>
Tcl_Channel
Tcl_GetStdChannel(type)
Tcl_SetStdChannel(channel, type)
ARGUMENTS
The identifier for the standard channel to retrieve or modify. Must be
one of TCL_STDIN, TCL_STDOUT, or TCL_STDERR. The channel to use as the
new value for the specified standard channel.
DESCRIPTION
Tcl defines three special channels that are used by various I/O related
commands if no other channels are specified. The standard input chan-
nel has a channel name of stdin and is used by read and gets. The
standard output channel is named stdout and is used by puts. The stan-
dard error channel is named stderr and is used for reporting errors.
In addition, the standard channels are inherited by any child processes
created using exec or open in the absence of any other redirections.
The standard channels are actually aliases for other normal channels.
The current channel associated with a standard channel can be retrieved
by calling Tcl_GetStdChannel with one of TCL_STDIN, TCL_STDOUT, or
TCL_STDERR as the type. The return value will be a valid channel, or
NULL.
A new channel can be set for the standard channel specified by type by
calling Tcl_SetStdChannel with a new channel or NULL in the channel
argument. If the specified channel is closed by a later call to
Tcl_Close, then the corresponding standard channel will automatically
be set to NULL.
If a non-NULL value for channel is passed to Tcl_SetStdChannel, then
that same value should be passed to Tcl_RegisterChannel, like so:
Tcl_RegisterChannel(NULL, channel); This is a workaround for a misfea-
ture in Tcl_SetStdChannel that it fails to do some reference counting
housekeeping. This misfeature cannot be corrected without contradict-
ing the assumptions of some existing code that calls Tcl_SetStdChannel.
If Tcl_GetStdChannel is called before Tcl_SetStdChannel, Tcl will con-
struct a new channel to wrap the appropriate platform-specific standard
file handle. If Tcl_SetStdChannel is called before Tcl_GetStdChannel,
then the default channel will not be created.
If one of the standard channels is set to NULL, either by calling
Tcl_SetStdChannel with a NULL channel argument, or by calling Tcl_Close
on the channel, then the next call to Tcl_CreateChannel will automati-
cally set the standard channel with the newly created channel. If more
than one standard channel is NULL, then the standard channels will be
assigned starting with standard input, followed by standard output,
with standard error being last.
See Tcl_StandardChannels for a general treatise about standard channels
and the behaviour of the Tcl library with regard to them.
SEE ALSO
Tcl_Close(3), Tcl_CreateChannel(3), Tcl_Main(3), tclsh(1)
KEYWORDS
standard channel, standard input, standard output, standard error
Tcl 7.5 Tcl_GetStdChannel(3)
GetStdChan 8.5.4 - Generated Tue Aug 19 08:27:02 CDT 2008