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Tcl_GetStdChannel(3)		      Tcl Library Procedures		     Tcl_GetStdChannel(3)

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NAME
       Tcl_GetStdChannel,  Tcl_SetStdChannel  - procedures for retrieving and replacing the stan-
       dard 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.
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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_SetStd-
       Channel 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 automat-
       ically be set to NULL.

       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 chan-
       nel.   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 behaviour
       of the Tcl library with regard to them.

SEE ALSO
       Tcl_Close(3), Tcl_CreateChannel(3), Tcl_Main(3), tclsh(1)

KEYWORDS
       standard channel, standard input, standard output, standard error

Tcl					       7.5			     Tcl_GetStdChannel(3)
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