--- /dev/null
+'\"
+'\" Copyright (c) 1989-1993 The Regents of the University of California.
+'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
+'\" Copyright (c) 2002 Kevin B. Kenny <kennykb@acm.org>. All rights reserved.
+'\"
+'\" See the file "license.terms" for information on usage and redistribution
+'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+'\"
+.TH Tcl_CreateTrace 3 "" Tcl "Tcl Library Procedures"
+.so man.macros
+.BS
+.SH NAME
+Tcl_CreateTrace, Tcl_CreateObjTrace, Tcl_DeleteTrace \- arrange for command execution to be traced
+.SH SYNOPSIS
+.nf
+\fB#include <tcl.h>\fR
+.sp
+Tcl_Trace
+\fBTcl_CreateTrace\fR(\fIinterp, level, proc, clientData\fR)
+.sp
+Tcl_Trace
+\fBTcl_CreateObjTrace\fR(\fIinterp, level, flags, objProc, clientData, deleteProc\fR)
+.sp
+\fBTcl_DeleteTrace\fR(\fIinterp, trace\fR)
+.SH ARGUMENTS
+.AS Tcl_CmdObjTraceDeleteProc *deleteProc
+.AP Tcl_Interp *interp in
+Interpreter containing command to be traced or untraced.
+.AP int level in
+Only commands at or below this nesting level will be traced unless
+0 is specified. 1 means
+top-level commands only, 2 means top-level commands or those that are
+invoked as immediate consequences of executing top-level commands
+(procedure bodies, bracketed commands, etc.) and so on.
+A value of 0 means that commands at any level are traced.
+.AP int flags in
+Flags governing the trace execution. See below for details.
+.AP Tcl_CmdObjTraceProc *objProc in
+Procedure to call for each command that is executed. See below for
+details of the calling sequence.
+.AP Tcl_CmdTraceProc *proc in
+Procedure to call for each command that is executed. See below for
+details on the calling sequence.
+.AP ClientData clientData in
+Arbitrary one-word value to pass to \fIobjProc\fR or \fIproc\fR.
+.AP Tcl_CmdObjTraceDeleteProc *deleteProc in
+Procedure to call when the trace is deleted. See below for details of
+the calling sequence. A NULL pointer is permissible and results in no
+callback when the trace is deleted.
+.AP Tcl_Trace trace in
+Token for trace to be removed (return value from previous call
+to \fBTcl_CreateTrace\fR).
+.BE
+.SH DESCRIPTION
+.PP
+\fBTcl_CreateObjTrace\fR arranges for command tracing. After it is
+called, \fIobjProc\fR will be invoked before the Tcl interpreter calls
+any command procedure when evaluating commands in \fIinterp\fR.
+The return value from \fBTcl_CreateObjTrace\fR is a token for the trace,
+which may be passed to \fBTcl_DeleteTrace\fR to remove the trace.
+There may be many traces in effect simultaneously for the same
+interpreter.
+.PP
+\fIobjProc\fR should have arguments and result that match the type,
+\fBTcl_CmdObjTraceProc\fR:
+.PP
+.CS
+typedef int \fBTcl_CmdObjTraceProc\fR(
+ \fBClientData\fR \fIclientData\fR,
+ \fBTcl_Interp\fR* \fIinterp\fR,
+ int \fIlevel\fR,
+ const char *\fIcommand\fR,
+ \fBTcl_Command\fR \fIcommandToken\fR,
+ int \fIobjc\fR,
+ \fBTcl_Obj\fR *const \fIobjv\fR[]);
+.CE
+.PP
+The \fIclientData\fR and \fIinterp\fR parameters are copies of the
+corresponding arguments given to \fBTcl_CreateTrace\fR.
+\fIClientData\fR typically points to an application-specific data
+structure that describes what to do when \fIobjProc\fR is invoked. The
+\fIlevel\fR parameter gives the nesting level of the command (1 for
+top-level commands passed to \fBTcl_Eval\fR by the application, 2 for
+the next-level commands passed to \fBTcl_Eval\fR as part of parsing or
+interpreting level-1 commands, and so on). The \fIcommand\fR parameter
+points to a string containing the text of the command, before any
+argument substitution. The \fIcommandToken\fR parameter is a Tcl
+command token that identifies the command to be invoked. The token
+may be passed to \fBTcl_GetCommandName\fR,
+\fBTcl_GetCommandInfoFromToken\fR, or \fBTcl_SetCommandInfoFromToken\fR to
+manipulate the definition of the command. The \fIobjc\fR and \fIobjv\fR
+parameters designate the final parameter count and parameter vector
+that will be passed to the command, and have had all substitutions
+performed.
+.PP
+The \fIobjProc\fR callback is expected to return a standard Tcl status
+return code. If this code is \fBTCL_OK\fR (the normal case), then
+the Tcl interpreter will invoke the command. Any other return code
+is treated as if the command returned that status, and the command is
+\fInot\fR invoked.
+.PP
+The \fIobjProc\fR callback must not modify \fIobjv\fR in any way. It
+is, however, permissible to change the command by calling
+\fBTcl_SetCommandTokenInfo\fR prior to returning. Any such change
+takes effect immediately, and the command is invoked with the new
+information.
+.PP
+Tracing will only occur for commands at nesting level less than
+or equal to the \fIlevel\fR parameter (i.e. the \fIlevel\fR
+parameter to \fIobjProc\fR will always be less than or equal to the
+\fIlevel\fR parameter to \fBTcl_CreateTrace\fR).
+.PP
+Tracing has a significant effect on runtime performance because it
+causes the bytecode compiler to refrain from generating in-line code
+for Tcl commands such as \fBif\fR and \fBwhile\fR in order that they
+may be traced. If traces for the built-in commands are not required,
+the \fIflags\fR parameter may be set to the constant value
+\fBTCL_ALLOW_INLINE_COMPILATION\fR. In this case, traces on built-in
+commands may or may not result in trace callbacks, depending on the
+state of the interpreter, but run-time performance will be improved
+significantly. (This functionality is desirable, for example, when
+using \fBTcl_CreateObjTrace\fR to implement an execution time
+profiler.)
+.PP
+Calls to \fIobjProc\fR will be made by the Tcl parser immediately before
+it calls the command procedure for the command (\fIcmdProc\fR). This
+occurs after argument parsing and substitution, so tracing for
+substituted commands occurs before tracing of the commands
+containing the substitutions. If there is a syntax error in a
+command, or if there is no command procedure associated with a
+command name, then no tracing will occur for that command. If a
+string passed to Tcl_Eval contains multiple commands (bracketed, or
+on different lines) then multiple calls to \fIobjProc\fR will occur,
+one for each command.
+.PP
+\fBTcl_DeleteTrace\fR removes a trace, so that no future calls will be
+made to the procedure associated with the trace. After \fBTcl_DeleteTrace\fR
+returns, the caller should never again use the \fItrace\fR token.
+.PP
+When \fBTcl_DeleteTrace\fR is called, the interpreter invokes the
+\fIdeleteProc\fR that was passed as a parameter to
+\fBTcl_CreateObjTrace\fR. The \fIdeleteProc\fR must match the type,
+\fBTcl_CmdObjTraceDeleteProc\fR:
+.PP
+.CS
+typedef void \fBTcl_CmdObjTraceDeleteProc\fR(
+ \fBClientData\fR \fIclientData\fR);
+.CE
+.PP
+The \fIclientData\fR parameter will be the same as the
+\fIclientData\fR parameter that was originally passed to
+\fBTcl_CreateObjTrace\fR.
+.PP
+\fBTcl_CreateTrace\fR is an alternative interface for command tracing,
+\fInot recommended for new applications\fR. It is provided for backward
+compatibility with code that was developed for older versions of the
+Tcl interpreter. It is similar to \fBTcl_CreateObjTrace\fR, except
+that its \fIproc\fR parameter should have arguments and result that
+match the type \fBTcl_CmdTraceProc\fR:
+.PP
+.CS
+typedef void \fBTcl_CmdTraceProc\fR(
+ ClientData \fIclientData\fR,
+ Tcl_Interp *\fIinterp\fR,
+ int \fIlevel\fR,
+ char *\fIcommand\fR,
+ Tcl_CmdProc *\fIcmdProc\fR,
+ ClientData \fIcmdClientData\fR,
+ int \fIargc\fR,
+ const char *\fIargv\fR[]);
+.CE
+.PP
+The parameters to the \fIproc\fR callback are similar to those of the
+\fIobjProc\fR callback above. The \fIcommandToken\fR is
+replaced with \fIcmdProc\fR, a pointer to the (string-based) command
+procedure that will be invoked; and \fIcmdClientData\fR, the client
+data that will be passed to the procedure. The \fIobjc\fR parameter
+is replaced with an \fIargv\fR parameter, that gives the arguments to
+the command as character strings.
+\fIProc\fR must not modify the \fIcommand\fR or \fIargv\fR strings.
+.PP
+If a trace created with \fBTcl_CreateTrace\fR is in effect, inline
+compilation of Tcl commands such as \fBif\fR and \fBwhile\fR is always
+disabled. There is no notification when a trace created with
+\fBTcl_CreateTrace\fR is deleted.
+There is no way to be notified when the trace created by
+\fBTcl_CreateTrace\fR is deleted. There is no way for the \fIproc\fR
+associated with a call to \fBTcl_CreateTrace\fR to abort execution of
+\fIcommand\fR.
+.SH KEYWORDS
+command, create, delete, interpreter, trace
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