path: root/usr/man/man3/Tcl_TraceCommand.3

'\"
'\" Copyright (c) 2002 Donal K. Fellows
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
.\" The -*- nroff -*- definitions below are for supplemental macros used
.\" in Tcl/Tk manual entries.
.\"
.\" .AP type name in/out ?indent?
.\"	Start paragraph describing an argument to a library procedure.
.\"	type is type of argument (int, etc.), in/out is either "in", "out",
.\"	or "in/out" to describe whether procedure reads or modifies arg,
.\"	and indent is equivalent to second arg of .IP (shouldn't ever be
.\"	needed;  use .AS below instead)
.\"
.\" .AS ?type? ?name?
.\"	Give maximum sizes of arguments for setting tab stops.  Type and
.\"	name are examples of largest possible arguments that will be passed
.\"	to .AP later.  If args are omitted, default tab stops are used.
.\"
.\" .BS
.\"	Start box enclosure.  From here until next .BE, everything will be
.\"	enclosed in one large box.
.\"
.\" .BE
.\"	End of box enclosure.
.\"
.\" .CS
.\"	Begin code excerpt.
.\"
.\" .CE
.\"	End code excerpt.
.\"
.\" .VS ?version? ?br?
.\"	Begin vertical sidebar, for use in marking newly-changed parts
.\"	of man pages.  The first argument is ignored and used for recording
.\"	the version when the .VS was added, so that the sidebars can be
.\"	found and removed when they reach a certain age.  If another argument
.\"	is present, then a line break is forced before starting the sidebar.
.\"
.\" .VE
.\"	End of vertical sidebar.
.\"
.\" .DS
.\"	Begin an indented unfilled display.
.\"
.\" .DE
.\"	End of indented unfilled display.
.\"
.\" .SO ?manpage?
.\"	Start of list of standard options for a Tk widget. The manpage
.\"	argument defines where to look up the standard options; if
.\"	omitted, defaults to "options". The options follow on successive
.\"	lines, in three columns separated by tabs.
.\"
.\" .SE
.\"	End of list of standard options for a Tk widget.
.\"
.\" .OP cmdName dbName dbClass
.\"	Start of description of a specific option.  cmdName gives the
.\"	option's name as specified in the class command, dbName gives
.\"	the option's name in the option database, and dbClass gives
.\"	the option's class in the option database.
.\"
.\" .UL arg1 arg2
.\"	Print arg1 underlined, then print arg2 normally.
.\"
.\" .QW arg1 ?arg2?
.\"	Print arg1 in quotes, then arg2 normally (for trailing punctuation).
.\"
.\" .PQ arg1 ?arg2?
.\"	Print an open parenthesis, arg1 in quotes, then arg2 normally
.\"	(for trailing punctuation) and then a closing parenthesis.
.\"
.\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
.ad b
.\"	# Start an argument description
.de AP
.ie !"\\$4"" .TP \\$4
.el \{\
.   ie !"\\$2"" .TP \\n()Cu
.   el          .TP 15
.\}
.ta \\n()Au \\n()Bu
.ie !"\\$3"" \{\
\&\\$1 \\fI\\$2\\fP (\\$3)
.\".b
.\}
.el \{\
.br
.ie !"\\$2"" \{\
\&\\$1	\\fI\\$2\\fP
.\}
.el \{\
\&\\fI\\$1\\fP
.\}
.\}
..
.\"	# define tabbing values for .AP
.de AS
.nr )A 10n
.if !"\\$1"" .nr )A \\w'\\$1'u+3n
.nr )B \\n()Au+15n
.\"
.if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n
.nr )C \\n()Bu+\\w'(in/out)'u+2n
..
.AS Tcl_Interp Tcl_CreateInterp in/out
.\"	# BS - start boxed text
.\"	# ^y = starting y location
.\"	# ^b = 1
.de BS
.br
.mk ^y
.nr ^b 1u
.if n .nf
.if n .ti 0
.if n \l'\\n(.lu\(ul'
.if n .fi
..
.\"	# BE - end boxed text (draw box now)
.de BE
.nf
.ti 0
.mk ^t
.ie n \l'\\n(^lu\(ul'
.el \{\
.\"	Draw four-sided box normally, but don't draw top of
.\"	box if the box started on an earlier page.
.ie !\\n(^b-1 \{\
\h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.el \}\
\h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.\}
.fi
.br
.nr ^b 0
..
.\"	# VS - start vertical sidebar
.\"	# ^Y = starting y location
.\"	# ^v = 1 (for troff;  for nroff this doesn't matter)
.de VS
.if !"\\$2"" .br
.mk ^Y
.ie n 'mc \s12\(br\s0
.el .nr ^v 1u
..
.\"	# VE - end of vertical sidebar
.de VE
.ie n 'mc
.el \{\
.ev 2
.nf
.ti 0
.mk ^t
\h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n'
.sp -1
.fi
.ev
.\}
.nr ^v 0
..
.\"	# Special macro to handle page bottom:  finish off current
.\"	# box/sidebar if in box/sidebar mode, then invoked standard
.\"	# page bottom macro.
.de ^B
.ev 2
'ti 0
'nf
.mk ^t
.if \\n(^b \{\
.\"	Draw three-sided box if this is the box's first page,
.\"	draw two sides but no top otherwise.
.ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.\}
.if \\n(^v \{\
.nr ^x \\n(^tu+1v-\\n(^Yu
\kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c
.\}
.bp
'fi
.ev
.if \\n(^b \{\
.mk ^y
.nr ^b 2
.\}
.if \\n(^v \{\
.mk ^Y
.\}
..
.\"	# DS - begin display
.de DS
.RS
.nf
.sp
..
.\"	# DE - end display
.de DE
.fi
.RE
.sp
..
.\"	# SO - start of list of standard options
.de SO
'ie '\\$1'' .ds So \\fBoptions\\fR
'el .ds So \\fB\\$1\\fR
.SH "STANDARD OPTIONS"
.LP
.nf
.ta 5.5c 11c
.ft B
..
.\"	# SE - end of list of standard options
.de SE
.fi
.ft R
.LP
See the \\*(So manual entry for details on the standard options.
..
.\"	# OP - start of full description for a single option
.de OP
.LP
.nf
.ta 4c
Command-Line Name:	\\fB\\$1\\fR
Database Name:	\\fB\\$2\\fR
Database Class:	\\fB\\$3\\fR
.fi
.IP
..
.\"	# CS - begin code excerpt
.de CS
.RS
.nf
.ta .25i .5i .75i 1i
..
.\"	# CE - end code excerpt
.de CE
.fi
.RE
..
.\"	# UL - underline word
.de UL
\\$1\l'|0\(ul'\\$2
..
.\"	# QW - apply quotation marks to word
.de QW
.ie '\\*(lq'"' ``\\$1''\\$2
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\$2
..
.\"	# PQ - apply parens and quotation marks to word
.de PQ
.ie '\\*(lq'"' (``\\$1''\\$2)\\$3
.\"" fix emacs highlighting
.el (\\*(lq\\$1\\*(rq\\$2)\\$3
..
.\"	# QR - quoted range
.de QR
.ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3
..
.\"	# MT - "empty" string
.de MT
.QW ""
..
.TH Tcl_TraceCommand 3 7.4 Tcl "Tcl Library Procedures"
.BS
.SH NAME
Tcl_CommandTraceInfo, Tcl_TraceCommand, Tcl_UntraceCommand \- monitor renames and deletes of a command
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
ClientData
\fBTcl_CommandTraceInfo(\fIinterp, cmdName, flags, proc, prevClientData\fB)\fR
.sp
int
\fBTcl_TraceCommand(\fIinterp, cmdName, flags, proc, clientData\fB)\fR
.sp
void
\fBTcl_UntraceCommand(\fIinterp, cmdName, flags, proc, clientData\fB)\fR
.SH ARGUMENTS
.AS Tcl_CommandTraceProc prevClientData
.AP Tcl_Interp *interp in
Interpreter containing the command.
.AP "const char" *cmdName in
Name of command.
.AP int flags in
OR'ed collection of the values \fBTCL_TRACE_RENAME\fR and
\fBTCL_TRACE_DELETE\fR.
.AP Tcl_CommandTraceProc *proc in
Procedure to call when specified operations occur to \fIcmdName\fR.
.AP ClientData clientData in
Arbitrary argument to pass to \fIproc\fR.
.AP ClientData prevClientData in
If non-NULL, gives last value returned by \fBTcl_CommandTraceInfo\fR,
so this call will return information about next trace.  If NULL, this
call will return information about first trace.
.BE
.SH DESCRIPTION
.PP
\fBTcl_TraceCommand\fR allows a C procedure to monitor operations
performed on a Tcl command, so that the C procedure is invoked
whenever the command is renamed or deleted.  If the trace is created
successfully then \fBTcl_TraceCommand\fR returns \fBTCL_OK\fR. If an error
occurred (e.g. \fIcmdName\fR specifies a non-existent command) then
\fBTCL_ERROR\fR is returned and an error message is left in the
interpreter's result.
.PP
The \fIflags\fR argument to \fBTcl_TraceCommand\fR indicates when the
trace procedure is to be invoked.  It consists of an OR'ed combination
of any of the following values:
.TP
\fBTCL_TRACE_RENAME\fR
Invoke \fIproc\fR whenever the command is renamed.
.TP
\fBTCL_TRACE_DELETE\fR
Invoke \fIproc\fR when the command is deleted.
.PP
Whenever one of the specified operations occurs to the command,
\fIproc\fR will be invoked.  It should have arguments and result that
match the type \fBTcl_CommandTraceProc\fR:
.CS
typedef void Tcl_CommandTraceProc(
        ClientData \fIclientData\fR,
        Tcl_Interp *\fIinterp\fR,
        const char *\fIoldName\fR,
        const char *\fInewName\fR,
        int \fIflags\fR);
.CE
The \fIclientData\fR and \fIinterp\fR parameters will have the same
values as those passed to \fBTcl_TraceCommand\fR when the trace was
created.  \fIClientData\fR typically points to an application-specific
data structure that describes what to do when \fIproc\fR is invoked.
\fIOldName\fR gives the name of the command being renamed, and
\fInewName\fR gives the name that the command is being renamed to (or
an empty string or NULL when the command is being deleted.)
\fIFlags\fR is an OR'ed combination of bits potentially providing
several pieces of information.  One of the bits \fBTCL_TRACE_RENAME\fR and
\fBTCL_TRACE_DELETE\fR will be set in \fIflags\fR to indicate which
operation is being performed on the command.  The bit
\fBTCL_TRACE_DESTROYED\fR will be set in \fIflags\fR if the trace is about
to be destroyed; this information may be useful to \fIproc\fR so that
it can clean up its own internal data structures (see the section
\fBTCL_TRACE_DESTROYED\fR below for more details).  Lastly, the bit
\fBTCL_INTERP_DESTROYED\fR will be set if the entire interpreter is being
destroyed.  When this bit is set, \fIproc\fR must be especially
careful in the things it does (see the section \fBTCL_INTERP_DESTROYED\fR
below).
.PP
\fBTcl_UntraceCommand\fR may be used to remove a trace.  If the
command specified by \fIinterp\fR, \fIcmdName\fR, and \fIflags\fR has
a trace set with \fIflags\fR, \fIproc\fR, and \fIclientData\fR, then
the corresponding trace is removed.  If no such trace exists, then the
call to \fBTcl_UntraceCommand\fR has no effect.  The same bits are
valid for \fIflags\fR as for calls to \fBTcl_TraceCommand\fR.
.PP
\fBTcl_CommandTraceInfo\fR may be used to retrieve information about
traces set on a given command.
The return value from \fBTcl_CommandTraceInfo\fR is the \fIclientData\fR
associated with a particular trace.
The trace must be on the command specified by the \fIinterp\fR,
\fIcmdName\fR, and \fIflags\fR arguments (note that currently the
flags are ignored; \fIflags\fR should be set to 0 for future
compatibility) and its trace procedure must the same as the \fIproc\fR
argument.
If the \fIprevClientData\fR argument is NULL then the return
value corresponds to the first (most recently created) matching
trace, or NULL if there are no matching traces.
If the \fIprevClientData\fR argument is not NULL, then it should
be the return value from a previous call to \fBTcl_CommandTraceInfo\fR.
In this case, the new return value will correspond to the next
matching trace after the one whose \fIclientData\fR matches
\fIprevClientData\fR, or NULL if no trace matches \fIprevClientData\fR
or if there are no more matching traces after it.
This mechanism makes it possible to step through all of the
traces for a given command that have the same \fIproc\fR.
.SH "CALLING COMMANDS DURING TRACES"
.PP
During rename traces, the command being renamed is visible with both
names simultaneously, and the command still exists during delete
traces (if \fBTCL_INTERP_DESTROYED\fR is not set).  However, there is no
mechanism for signaling that an error occurred in a trace procedure,
so great care should be taken that errors do not get silently lost.
.SH "MULTIPLE TRACES"
.PP
It is possible for multiple traces to exist on the same command.
When this happens, all of the trace procedures will be invoked on each
access, in order from most-recently-created to least-recently-created.
Attempts to delete the command during a delete trace will fail
silently, since the command is already scheduled for deletion anyway.
If the command being renamed is renamed by one of its rename traces,
that renaming takes precedence over the one that triggered the trace
and the collection of traces will not be reexecuted; if several traces
rename the command, the last renaming takes precedence.
.SH "TCL_TRACE_DESTROYED FLAG"
.PP
In a delete callback to \fIproc\fR, the \fBTCL_TRACE_DESTROYED\fR bit
is set in \fIflags\fR.
.\" Perhaps need some more comments here? - DKF
.SH "TCL_INTERP_DESTROYED"
.PP
When an interpreter is destroyed, unset traces are called for
all of its commands.
The \fBTCL_INTERP_DESTROYED\fR bit will be set in the \fIflags\fR
argument passed to the trace procedures.
Trace procedures must be extremely careful in what they do if
the \fBTCL_INTERP_DESTROYED\fR bit is set.
It is not safe for the procedures to invoke any Tcl procedures
on the interpreter, since its state is partially deleted.
All that trace procedures should do under these circumstances is
to clean up and free their own internal data structures.
.SH BUGS
.PP
Tcl does not do any error checking to prevent trace procedures
from misusing the interpreter during traces with \fBTCL_INTERP_DESTROYED\fR
set.
.SH KEYWORDS
clientData, trace, command