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
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 chan-
nel.
_________________________________________________________________DESCRIPTION
Tcl defines three special channels that are used by vari-
ous I/O related commands if no other channels are speci-
fied. 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 nor-
mal channels. The current channel associated with a stan-
dard 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 speci-
fied by type by calling Tcl_SetStdChannel with a new chan-
nel 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.
Tcl 7.5 1
Tcl_GetStdChannel(3) Tcl Library Procedures 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_SetStd-
Channel 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 ALSOTcl_Close(3), Tcl_CreateChannel(3)KEYWORDS
standard channel, standard input, standard output, stan-
dard error
Tcl 7.5 2
