Tcl_GetStdChannel(3) Tcl (7.5) 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
int type (in) The identifier for the
standard channel to
retrieve or modify. Must
be one of TCL_STDIN,
TCL_STDOUT, or TCL_STDERR.
Tcl_Channel channel (in) 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 channel 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 standard 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.
Page 1 (printed 2/19/99)
Tcl_GetStdChannel(3) Tcl (7.5) Tcl_GetStdChannel(3)
If Tcl_GetStdChannel is called before Tcl_SetStdChannel, Tcl
will construct 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 automatically 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 ALSO
Tcl_Close(3), Tcl_CreateChannel(3)
KEYWORDS
standard channel, standard input, standard output, standard
error
Page 2 (printed 2/19/99)
