1Tcl_StackChannel(3) Tcl Library Procedures Tcl_StackChannel(3)
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6
8 Tcl_StackChannel, Tcl_UnstackChannel, Tcl_GetStackedChannel, Tcl_Get‐
9 TopChannel - manipulate stacked I/O channels
10
12 #include <tcl.h>
13 Tcl_Channel
15 Tcl_StackChannel(interp, typePtr, clientData, mask, channel)
16 int
18 Tcl_UnstackChannel(interp, channel)
19 Tcl_Channel
21 Tcl_GetStackedChannel(channel)
22 Tcl_Channel
24 Tcl_GetTopChannel(channel)
25
28 Tcl_Interp *interp (in) Interpreter for error report‐
29 ing.
30 Tcl_ChannelType *typePtr (in) The new channel I/O procedures
32 to use for channel.
33 ClientData clientData (in) Arbitrary one-word value to
35 pass to channel I/O proce‐
36 dures.
37 int mask (in) Conditions under which channel
39 will be used: OR-ed combina‐
40 tion of TCL_READABLE,
41 TCL_WRITABLE and TCL_EXCEP‐
42 TION. This can be a subset of
43 the operations currently
44 allowed on channel.
45 Tcl_Channel channel (in) An existing Tcl channel such
47 as returned by Tcl_CreateChan‐
48 nel.
49_________________________________________________________________
50
53 These functions are for use by extensions that add processing layers to
54 Tcl I/O channels. Examples include compression and encryption modules.
55 These functions transparently stack and unstack a new channel on top of
56 an existing one. Any number of channels can be stacked together.
57 The implementation of the Tcl channel code was rewritten in 8.3.2 to
59 correct some problems with the previous implementation with regard to
60 stacked channels. Anyone using stacked channels or creating stacked
61 channel drivers should update to the new TCL_CHANNEL_VERSION_2
62 Tcl_ChannelType structure. See Tcl_CreateChannel for details.
63 Tcl_StackChannel stacks a new channel on an existing channel with the
65 same name that was registered for channel by Tcl_RegisterChannel.
66 Tcl_StackChannel works by creating a new channel structure and placing
68 itself on top of the channel stack. EOL translation, encoding and
69 buffering options are shared between all channels in the stack. The
70 hidden channel does no buffering, newline translations, or character
71 set encoding. Instead, the buffering, newline translations, and encod‐
72 ing functions all remain at the top of the channel stack. A pointer to
73 the new top channel structure is returned. If an error occurs when
74 stacking the channel, NULL is returned instead.
75 The mask parameter specifies the operations that are allowed on the new
77 channel. These can be a subset of the operations allowed on the origi‐
78 nal channel. For example, a read-write channel may become read-only
79 after the Tcl_StackChannel call.
80 Closing a channel closes the channels stacked below it. The close of
82 stacked channels is executed in a way that allows buffered data to be
83 properly flushed.
84 Tcl_UnstackChannel reverses the process. The old channel is associated
86 with the channel name, and the processing module added by
87 Tcl_StackChannel is destroyed. If there is no old channel, then
88 Tcl_UnstackChannel is equivalent to Tcl_Close. If an error occurs
89 unstacking the channel, TCL_ERROR is returned, otherwise TCL_OK is
90 returned.
91 Tcl_GetTopChannel returns the top channel in the stack of channels the
93 supplied channel is part of.
94 Tcl_GetStackedChannel returns the channel in the stack of channels
96 which is just below the supplied channel.
97
100 Notifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).
101
104 channel, compression
105Tcl 8.3 Tcl_StackChannel(3)