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Tcl_CreateTrace(3) Tcl Library Procedures Tcl_CreateTrace(3)
Tcl_CreateTrace, Tcl_CreateObjTrace, Tcl_DeleteTrace - arrange for
command execution to be traced
Tcl_CreateTrace(interp, level, proc, clientData)
Tcl_CreateObjTrace(interp, level, flags, objProc, clientData, deleteProc)
Tcl_Interp *interp (in) Interpreter
to be traced or
int level (in) Only commands at or
below this nesting
level will be
traced unless 0 is
specified. 1 means
only, 2 means top-
level commands or
those that are
commands, etc.) and
so on. A value of
0 means that
commands at any
level are traced.
int flags (in) Flags governing the
See below for
Tcl_CmdObjTraceProc *objProc (in) Procedure to call
for each command
that is executed.
See below for
details of the
Tcl_CmdTraceProc *proc (in) Procedure to call
for each command
that is executed.
See below for
details on the
ClientData clientData (in) Arbitrary one-word
value to pass to
objProc or proc.
Tcl_CmdObjTraceDeleteProc *deleteProc (in) Procedure to call
when the trace is
deleted. See below
for details of the
A NULL pointer is
results in no
callback when the
trace is deleted.
Tcl_Trace trace (in) Token for trace to
be removed (return
value from previous
Tcl_CreateObjTrace arranges for command tracing. After it is called,
objProc will be invoked before the Tcl interpreter calls any command
procedure when evaluating commands in interp. The return value from
Tcl_CreateObjTrace 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 interpreter.
objProc should have arguments and result that match the type,
typedef int Tcl_CmdObjTraceProc(
const char *command,
Tcl_Obj *const objv);
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
objProc is invoked. The level parameter gives the nesting level of the
command (1 for top-level commands passed to Tcl_Eval by the
application, 2 for the next-level commands passed to Tcl_Eval as part
of parsing or interpreting level-1 commands, and so on). The command
parameter points to a string containing the text of the command, before
any argument substitution. The commandToken parameter is a Tcl command
token that identifies the command to be invoked. The token may be
passed to Tcl_GetCommandName, Tcl_GetCommandInfoFromToken, or
Tcl_SetCommandInfoFromToken to manipulate the definition of the
command. The objc and objv parameters designate the final parameter
count and parameter vector that will be passed to the command, and have
had all substitutions performed.
The objProc callback is expected to return a standard Tcl status return
code. If this code is TCL_OK (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 not invoked.
The objProc callback must not modify objv in any way. It is, however,
permissible to change the command by calling Tcl_SetCommandTokenInfo
prior to returning. Any such change takes effect immediately, and the
command is invoked with the new information.
Tracing will only occur for commands at nesting level less than or
equal to the level parameter (i.e. the level parameter to objProc will
always be less than or equal to the level parameter to
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 if and while in order that they may be traced.
If traces for the built-in commands are not required, the flags
parameter may be set to the constant value
TCL_ALLOW_INLINE_COMPILATION. 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 Tcl_CreateObjTrace to implement an execution time profiler.)
Calls to objProc 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 objProc will occur, one for each command.
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.
When Tcl_DeleteTrace is called, the interpreter invokes the deleteProc
that was passed as a parameter to Tcl_CreateObjTrace. The deleteProc
must match the type, Tcl_CmdObjTraceDeleteProc:
typedef void Tcl_CmdObjTraceDeleteProc(
The clientData parameter will be the same as the clientData parameter
that was originally passed to Tcl_CreateObjTrace.
Tcl_CreateTrace is an alternative interface for command tracing, not
recommended for new applications. It is provided for backward
compatibility with code that was developed for older versions of the
Tcl interpreter. It is similar to Tcl_CreateObjTrace, except that its
proc parameter should have arguments and result that match the type
typedef void Tcl_CmdTraceProc(
const char *argv);
The parameters to the proc callback are similar to those of the objProc
callback above. The commandToken is replaced with cmdProc, a pointer to
the (string-based) command procedure that will be invoked; and
cmdClientData, the client data that will be passed to the procedure.
The objc parameter is replaced with an argv parameter, that gives the
arguments to the command as character strings. Proc must not modify
the command or argv strings.
If a trace created with Tcl_CreateTrace is in effect, inline
compilation of Tcl commands such as if and while is always disabled.
There is no notification when a trace created with Tcl_CreateTrace is
deleted. There is no way to be notified when the trace created by
Tcl_CreateTrace is deleted. There is no way for the proc associated
with a call to Tcl_CreateTrace to abort execution of command.
command, create, delete, interpreter, trace