TclGetStdChannel(3) Tcl Library Procedures TclGetStdChannel(3)

NAME
       TclGetStdChannel,  TclSetStdChannel  -  procedures for retrieving and
       replacing the standard channels

SYNOPSIS
       ##iinncclluuddee <>

       TclChannel
       TTccllGGeettSSttddCChhaannnneell(type)

       TTccllSSeettSSttddCChhaannnneell(channel, type)


AARRGGUUMMEENNTTSS
       int           type      (in)      The identifier for the standard chan-
                                         nel  to  retrieve or modify.  Must be
                                         one  of  TTCCLLSSTTDDIINN,  TTCCLLSSTTDDOOUUTT,   or
                                         TTCCLLSSTTDDEERRRR.

       TclChannel   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 chan-
       nel has a channel name of ssttddiinn and is used  by  rreeaadd  and  ggeettss.   The
       standard output channel is named ssttddoouutt and is used by ppuuttss.  The stan-
       dard error channel is named ssttddeerrrr and is used  for  reporting  errors.
       In addition, the standard channels are inherited by any child processes
       created using eexxeecc or ooppeenn 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 TTccllGGeettSSttddCChhaannnneell with  one  of  TTCCLLSSTTDDIINN,  TTCCLLSSTTDDOOUUTT,  or
       TTCCLLSSTTDDEERRRR  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  TTccllSSeettSSttddCChhaannnneell  with  a  new channel or NULL in the channel
       argument.  If the specified channel  is  closed  by  a  later  call  to
       TTccllCClloossee,  then  the corresponding standard channel will automatically
       be set to NULL.

       If TTccllGGeettSSttddCChhaannnneell is called before TTccllSSeettSSttddCChhaannnneell, Tcl will  con-
       struct a new channel to wrap the appropriate platform-specific standard
       file handle.  If TTccllSSeettSSttddCChhaannnneell is called before  TTccllGGeettSSttddCChhaannnneell,
       then the default channel will not be created.

       If  one  of  the  standard  channels  is set to NULL, either by calling
       TTccllSSeettSSttddCChhaannnneell with a NULL channel argument, or by calling TTccllCClloossee
       on  the channel, then the next call to TTccllCCrreeaatteeCChhaannnneell 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 TTccllSSttaannddaarrddCChhaannnneellss for a general treatise about standard channels
       and the behaviour of the Tcl library with regard to them.



SEE ALSO
       TclClose(3), TclCreateChannel(3), TclMain(3), tclsh(1)


KKEEYYWWOORRDDSS
       standard channel, standard input, standard output, standard error



Tcl                                   7.5                 TclGetStdChannel(3)