DragonFly On-Line Manual Pages
Tcl_GetStdChannel(3) Tcl Library Procedures Tcl_GetStdChannel(3)
Tcl_GetStdChannel, Tcl_SetStdChannel - procedures for retrieving and
replacing the standard channels
int type (in) The identifier for the standard
channel to retrieve or modify. Must
be one of TCL_STDIN, TCL_STDOUT, or
Tcl_Channel channel (in) The channel to use as the new value
for the specified standard channel.
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
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
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:
This is a workaround for a misfeature in Tcl_SetStdChannel that it
fails to do some reference counting housekeeping. This misfeature
cannot be corrected without contradicting the assumptions of some
existing code that calls Tcl_SetStdChannel.
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 Tcl_StandardChannels for a general treatise about standard channels
and the behavior of the Tcl library with regard to them.
Tcl_Close(3), Tcl_CreateChannel(3), Tcl_Main(3), tclsh(1)
standard channel, standard input, standard output, standard error
Tcl 7.5 Tcl_GetStdChannel(3)