141 lines
6.0 KiB
Groff
141 lines
6.0 KiB
Groff
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'\"
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'\" Copyright (c) 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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.TH Tcl_SetChannelError 3 8.5 Tcl "Tcl Library Procedures"
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.so man.macros
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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Tcl_SetChannelError, Tcl_SetChannelErrorInterp, Tcl_GetChannelError, Tcl_GetChannelErrorInterp \- functions to create/intercept Tcl errors by channel drivers.
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.SH SYNOPSIS
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.nf
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\fB#include <tcl.h>\fR
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.sp
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void
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\fBTcl_SetChannelError\fR(\fIchan, msg\fR)
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.sp
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void
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\fBTcl_SetChannelErrorInterp\fR(\fIinterp, msg\fR)
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.sp
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void
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\fBTcl_GetChannelError\fR(\fIchan, msgPtr\fR)
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.sp
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void
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\fBTcl_GetChannelErrorInterp\fR(\fIinterp, msgPtr\fR)
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.sp
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.SH ARGUMENTS
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.AS Tcl_Channel chan
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.AP Tcl_Channel chan in
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Refers to the Tcl channel whose bypass area is accessed.
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.AP Tcl_Interp* interp in
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Refers to the Tcl interpreter whose bypass area is accessed.
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.AP Tcl_Obj* msg in
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Error message put into a bypass area. A list of return options and values,
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followed by a string message. Both message and the option/value information
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are optional.
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.AP Tcl_Obj** msgPtr out
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Reference to a place where the message stored in the accessed bypass area can
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be stored in.
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.BE
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.SH DESCRIPTION
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.PP
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The current definition of a Tcl channel driver does not permit the direct
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return of arbitrary error messages, except for the setting and retrieval of
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channel options. All other functions are restricted to POSIX error codes.
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.PP
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The functions described here overcome this limitation. Channel drivers are
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allowed to use \fBTcl_SetChannelError\fR and \fBTcl_SetChannelErrorInterp\fR
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to place arbitrary error messages in \fBbypass areas\fR defined for channels
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and interpreters. And the generic I/O layer uses \fBTcl_GetChannelError\fR and
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\fBTcl_GetChannelErrorInterp\fR to look for messages in the bypass areas and
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arrange for their return as errors. The POSIX error codes set by a driver are
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used now if and only if no messages are present.
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.PP
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\fBTcl_SetChannelError\fR stores error information in the bypass area of the
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specified channel. The number of references to the \fBmsg\fR value goes up by
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one. Previously stored information will be discarded, by releasing the
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reference held by the channel. The channel reference must not be NULL.
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.PP
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\fBTcl_SetChannelErrorInterp\fR stores error information in the bypass area of
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the specified interpreter. The number of references to the \fBmsg\fR value
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goes up by one. Previously stored information will be discarded, by releasing
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the reference held by the interpreter. The interpreter reference must not be
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NULL.
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.PP
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\fBTcl_GetChannelError\fR places either the error message held in the bypass
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area of the specified channel into \fImsgPtr\fR, or NULL; and resets the
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bypass, that is, after an invocation all following invocations will return
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NULL, until an intervening invocation of \fBTcl_SetChannelError\fR with a
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non-NULL message. The \fImsgPtr\fR must not be NULL. The reference count of
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the message is not touched. The reference previously held by the channel is
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now held by the caller of the function and it is its responsibility to release
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that reference when it is done with the value.
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.PP
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\fBTcl_GetChannelErrorInterp\fR places either the error message held in the
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bypass area of the specified interpreter into \fImsgPtr\fR, or NULL; and
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resets the bypass, that is, after an invocation all following invocations will
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return NULL, until an intervening invocation of
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\fBTcl_SetChannelErrorInterp\fR with a non-NULL message. The \fImsgPtr\fR must
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not be NULL. The reference count of the message is not touched. The reference
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previously held by the interpreter is now held by the caller of the function
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and it is its responsibility to release that reference when it is done with
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the value.
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.PP
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Which functions of a channel driver are allowed to use which bypass function
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is listed below, as is which functions of the public channel API may leave a
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messages in the bypass areas.
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.IP \fBTcl_DriverCloseProc\fR
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May use \fBTcl_SetChannelErrorInterp\fR, and only this function.
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.IP \fBTcl_DriverInputProc\fR
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May use \fBTcl_SetChannelError\fR, and only this function.
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.IP \fBTcl_DriverOutputProc\fR
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May use \fBTcl_SetChannelError\fR, and only this function.
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.IP \fBTcl_DriverSeekProc\fR
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May use \fBTcl_SetChannelError\fR, and only this function.
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.IP \fBTcl_DriverWideSeekProc\fR
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May use \fBTcl_SetChannelError\fR, and only this function.
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.IP \fBTcl_DriverSetOptionProc\fR
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Has already the ability to pass arbitrary error messages. Must \fInot\fR use
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any of the new functions.
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.IP \fBTcl_DriverGetOptionProc\fR
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Has already the ability to pass arbitrary error messages. Must
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\fInot\fR use any of the new functions.
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.IP \fBTcl_DriverWatchProc\fR
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Must \fInot\fR use any of the new functions. Is internally called and has no
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ability to return any type of error whatsoever.
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.IP \fBTcl_DriverBlockModeProc\fR
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May use \fBTcl_SetChannelError\fR, and only this function.
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.IP \fBTcl_DriverGetHandleProc\fR
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Must \fInot\fR use any of the new functions. It is only a low-level function,
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and not used by Tcl commands.
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.IP \fBTcl_DriverHandlerProc\fR
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Must \fInot\fR use any of the new functions. Is internally called and has no
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ability to return any type of error whatsoever.
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.PP
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Given the information above the following public functions of the Tcl C API
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are affected by these changes; when these functions are called, the channel
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may now contain a stored arbitrary error message requiring processing by the
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caller.
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.DS
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.ta 1.9i 4i
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\fBTcl_Flush\fR \fBTcl_GetsObj\fR \fBTcl_Gets\fR
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\fBTcl_ReadChars\fR \fBTcl_ReadRaw\fR \fBTcl_Read\fR
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\fBTcl_Seek\fR \fBTcl_StackChannel\fR \fBTcl_Tell\fR
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\fBTcl_WriteChars\fR \fBTcl_WriteObj\fR \fBTcl_WriteRaw\fR
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\fBTcl_Write\fR
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.DE
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.PP
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All other API functions are unchanged. In particular, the functions below
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leave all their error information in the interpreter result.
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.DS
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.ta 1.9i 4i
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\fBTcl_Close\fR \fBTcl_UnstackChannel\fR \fBTcl_UnregisterChannel\fR
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.DE
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.SH "SEE ALSO"
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Tcl_Close(3), Tcl_OpenFileChannel(3), Tcl_SetErrno(3)
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.SH KEYWORDS
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channel driver, error messages, channel type
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