Tcl_CreateTrace(3) Tcl Tcl_CreateTrace(3)
_________________________________________________________________
NAME
Tcl_CreateTrace, Tcl_DeleteTrace - arrange for command
execution to be traced
SYNOPSIS
#include <tcl.h>
Tcl_Trace
Tcl_CreateTrace(interp, level, proc, clientData)
Tcl_DeleteTrace(interp, trace)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter
containing
command to be
traced or
untraced.
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
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Tcl_CreateTrace(3) Tcl Tcl_CreateTrace(3)
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
Tcl_CreateTrace).
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DESCRIPTION
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.
Proc should have arguments and result that match the type
Tcl_CmdTraceProc:
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 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).
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
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Tcl_CreateTrace(3) Tcl Tcl_CreateTrace(3)
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_Eval.
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.
KEYWORDS
command, create, delete, interpreter, trace
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