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  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 ALSO

       Tcl_Close(3), Tcl_CreateChannel(3)



KEYWORDS

       standard  channel,  standard input, standard output, stan­
       dard error