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Tcl_CreateTrace(3Tcl)					 Tcl_CreateTrace(3Tcl)

NAME    [Toc]    [Back]

     Tcl_CreateTrace, Tcl_DeleteTrace -	arrange	for command execution to be

SYNOPSIS    [Toc]    [Back]

     #include <tcl.h>

     Tcl_CreateTrace(interp, level, proc, clientData)

     Tcl_DeleteTrace(interp, trace)

ARGUMENTS    [Toc]    [Back]

     Tcl_Interp		*interp		 (in)	   Interpreter containing
						   command to be traced	or

     int		level		 (in)	   Only	commands at or below
						   this	nesting	level will be
						   traced.  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.

     Tcl_CmdTraceProc	*proc		 (in)	   Procedure to	call for each
						   command that's executed.
						   See below for details on
						   the calling sequence.

     ClientData		clientData	 (in)	   Arbitrary one-word value to
						   pass	to proc.

     Tcl_Trace		trace		 (in)	   Token for trace to be
						   removed (return value from
						   previous call to

DESCRIPTION    [Toc]    [Back]

     Tcl_CreateTrace arranges for command tracing.  From now on, proc will be
     invoked before Tcl	calls command procedures to process commands in
     interp.  The return value from Tcl_CreateTrace is a token for the trace,
     which may be passed to Tcl_DeleteTrace to remove the trace.  There	may be
     many traces in effect simultaneously for the same command interpreter.

									Page 1

Tcl_CreateTrace(3Tcl)					 Tcl_CreateTrace(3Tcl)

     Proc should have arguments	and result that	match the type

	  typedef void Tcl_CmdTraceProc(
	       ClientData clientData,
	       Tcl_Interp *interp,
	       int level,
	       char *command,
	       Tcl_CmdProc *cmdProc,
	       ClientData cmdClientData,
	       int argc,
	       char *argv[]));

     The clientData and	interp parameters are copies of	the corresponding
     arguments given to	Tcl_CreateTrace.  ClientData typically points to an
     application-specific data structure that describes	what to	do when	proc
     is	invoked.  Level	gives the nesting level	of the command (1 for toplevel
 commands passed to Tcl_Eval by the application, 2 for the nextlevel
 commands passed to Tcl_Eval as part of parsing or interpreting
     level-1 commands, and so on).  Command points to a	string containing the
     text of the command, before any argument substitution.  CmdProc contains
     the address of the	command	procedure that will be called to process the
     command (i.e. the proc argument of	some previous call to
     Tcl_CreateCommand)	and cmdClientData contains the associated client data
     for cmdProc (the clientData value passed to Tcl_CreateCommand).  Argc and
     argv give the final argument information that will	be passed to cmdProc,
     after command, variable, and backslash substitution.  Proc	must not
     modify the	command	or argv	strings.

     Tracing will only occur for commands at nesting level less	than or	equal
     to	the level parameter (i.e. the level parameter to proc will always be
     less than or equal	to the level parameter to Tcl_CreateTrace).

     Calls to proc will	be made	by the Tcl parser immediately before it	calls
     the command procedure for the command (cmdProc).  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 proc will
     occur, one	for each command.  The command string for each of these	trace
     calls will	reflect	only a single command, not the entire string passed to

     Tcl_DeleteTrace removes a trace, so that no future	calls will be made to
     the procedure associated with the trace.  After Tcl_DeleteTrace returns,
     the caller	should never again use the trace token.

									Page 2

Tcl_CreateTrace(3Tcl)					 Tcl_CreateTrace(3Tcl)

KEYWORDS    [Toc]    [Back]

     command, create, delete, interpreter, trace

									PPPPaaaaggggeeee 3333
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