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CentOS 7.0 - man page for tcl_gettopchannel (centos section 3)

Tcl_StackChannel(3)		      Tcl Library Procedures		      Tcl_StackChannel(3)

_________________________________________________________________________________________________

NAME
       Tcl_StackChannel,  Tcl_UnstackChannel,  Tcl_GetStackedChannel, Tcl_GetTopChannel - manipu-
       late stacked I/O channels

SYNOPSIS
       #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)

ARGUMENTS
       Tcl_Interp *interp (in)			Interpreter for error reporting.

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

       ClientData 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 oper-
						ations currently allowed on channel.

       Tcl_Channel channel (in) 		An  existing  Tcl  channel  such  as  returned by
						Tcl_CreateChannel.
_________________________________________________________________

DESCRIPTION
       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 implementation of the Tcl channel code was rewritten in 8.3.2 to correct some problems
       with the previous implementation with regard to stacked channels.   Anyone  using  stacked
       channels  or  creating  stacked	channel drivers should update to the new TCL_CHANNEL_VER-
       SION_2 Tcl_ChannelType structure.  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  func-
       tions all remain at the top of the channel stack.  A pointer to the new top channel struc-
       ture 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.

SEE ALSO
       Notifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).

KEYWORDS
       channel, compression

Tcl					       8.3			      Tcl_StackChannel(3)


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