Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel, Tcl_GetTopChannel - manipulate stacked I/O

       Tcl_Interp *interp (in)                  Interpreter for error reporting.

       const Tcl_ChannelType *typePtr (in)      The new channel I/O procedures to use for channel.

       void *clientData (in)                    Arbitrary one-word value to pass to channel I/O procedures.

       int mask (in)                            Conditions under which channel will be used:  OR-ed  combination
                                                of  TCL_READABLE, TCL_WRITABLE and TCL_EXCEPTION.  This can be a
                                                subset of the operations currently allowed on channel.

       Tcl_Channel channel (in)                 An existing Tcl channel such as returned by Tcl_CreateChannel.
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       These functions are for use by extensions that add processing  layers  to  Tcl  I/O  channels.   Examples
       include  compression  and  encryption  modules.   These  functions  transparently stack and unstack a new
       channel on top of an existing one.  Any number of channels can be stacked together.

       The Tcl_ChannelType version currently supported  is  TCL_CHANNEL_VERSION_5.   See  Tcl_CreateChannel  for
       details.

       Tcl_StackChannel  stacks  a new channel on an existing channel with the same name that was registered for
       channel by Tcl_RegisterChannel.

       Tcl_StackChannel works by creating a new channel structure and placing  itself  on  top  of  the  channel
       stack.   EOL  translation,  encoding  and buffering options are shared between all channels in the stack.
       The hidden channel does no buffering, newline translations, or  character  set  encoding.   Instead,  the
       buffering,  newline  translations,  and encoding functions all remain at the top of the channel stack.  A
       pointer to the new top channel structure is returned.  If an error occurs when stacking the channel, NULL
       is returned instead.

       The mask parameter specifies the operations that are allowed on the new channel.  These can be  a  subset
       of  the  operations  allowed on the original channel.  For example, a read-write channel may become read-
       only after the Tcl_StackChannel call.

       Closing a channel closes the channels stacked below it.  The close of stacked channels is executed  in  a
       way that allows buffered data to be properly flushed.

       Tcl_UnstackChannel  reverses  the  process.  The old channel is associated with the channel name, and the
       processing  module  added  by  Tcl_StackChannel  is  destroyed.   If  there  is  no  old  channel,   then
       Tcl_UnstackChannel  is  equivalent to Tcl_Close.  If an error occurs unstacking the channel, TCL_ERROR is
       returned, otherwise TCL_OK is returned.

       Tcl_GetTopChannel returns the top channel in the stack of channels the supplied channel is part of.

       Tcl_GetStackedChannel returns the channel in the stack of channels  which  is  just  below  the  supplied
       channel.

       channel, compression

Tcl                                                    8.3                                Tcl_StackChannel(3tcl)

       Tcl_StackChannel,  Tcl_UnstackChannel,  Tcl_GetStackedChannel, Tcl_GetTopChannel - manipulate stacked I/O
       channels

Notifier(3tcl), Tcl_CreateChannel(3tcl), Tcl_OpenFileChannel(3tcl), vwait(3tcl)

#include<tcl.h>

       Tcl_Channel
       Tcl_StackChannel(interp,typePtr,clientData,mask,channel)

       int
       Tcl_UnstackChannel(interp,channel)

       Tcl_Channel
       Tcl_GetStackedChannel(channel)

       Tcl_Channel
       Tcl_GetTopChannel(channel)