Scroll to navigation

Tcl_StackChannel(3tcl) Tcl Library Procedures Tcl_StackChannel(3tcl) 





NAME


Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel,
    Tcl_GetTopChannel - manipulate 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.

  
const Tcl_ChannelType *typePtr (in)

  
The new channel I/O procedures to use for channel.

  
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 operations 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_VERSION_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
    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.








SEE ALSO


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








KEYWORDS


channel, compression







  

    8.3
    Tcl