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NAME
Tcl_CreateTrace, Tcl_DeleteTrace - arrange for command exe-
cution 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 com-
mands or those
that are
invoked as
immediate
consequences
of executing
top-level com-
mands (pro-
cedure bodies,
bracketed com-
mands, 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
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. Client-
Data typically points to an application-specific data struc-
ture that describes what to do when proc is invoked. Level
gives the nesting level of the command (1 for top-level com-
mands 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 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 parame-
ter 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 substitu-
tion, 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 com-
mand procedure associated with a command name, then no trac-
ing will occur for that command. If a string passed to
Tcl_Eval contains multiple commands (bracketed, or on dif-
ferent 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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