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.so man.macros

.TH Tcl_CreateTrace 3 "" Tcl "Tcl Library Procedures"

.BS

.SH NAME

Tcl_CreateTrace, Tcl_DeleteTrace \- arrange for command execution to be traced

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

Tcl_Trace

\fBTcl_CreateTrace\fR(\fIinterp, level, proc, clientData\fR)

.sp

\fBTcl_DeleteTrace\fR(\fIinterp, trace\fR)

.SH ARGUMENTS

.AS Tcl_CmdTraceProc (clientData)()

.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.  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.

.AP Tcl_CmdTraceProc *proc in

Procedure to call for each command that's executed.  See below for

details on the calling sequence.

.AP ClientData clientData in

Arbitrary one-word value to pass to \fIproc\fR.

.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_CreateTrace\fR arranges for command tracing.  From now on, \fIproc\fR

will be invoked before Tcl calls command procedures to process

commands in \fIinterp\fR.  The return value from

\fBTcl_CreateTrace\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 command interpreter.

.PP

\fIProc\fR should have arguments and result that match the

type \fBTcl_CmdTraceProc\fR:

.CS

typedef void Tcl_CmdTraceProc(

        ClientData \fIclientData\fR,

        Tcl_Interp *\fIinterp\fR,

        int \fIlevel\fR,

        char *\fIcommand\fR,

        Tcl_CmdProc *\fIcmdProc\fR,

        ClientData \fIcmdClientData\fR,

        int \fIargc\fR,

        char *\fIargv\fR[]);

.CE

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 \fIproc\fR

is invoked.  \fILevel\fR 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).  \fICommand\fR

points to a string containing the text of the

command, before any argument substitution.

\fICmdProc\fR contains the address of the command procedure that

will be called to process the command (i.e. the \fIproc\fR argument

of some previous call to \fBTcl_CreateCommand\fR) and \fIcmdClientData\fR

contains the associated client data for \fIcmdProc\fR (the \fIclientData\fR

value passed to \fBTcl_CreateCommand\fR).  \fIArgc\fR and \fIargv\fR give

the final argument information that will be passed to \fIcmdProc\fR, after

command, variable, and backslash substitution.

\fIProc\fR must not modify the \fIcommand\fR or \fIargv\fR strings.

.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 \fIproc\fR will always be less than or equal to the

\fIlevel\fR parameter to \fBTcl_CreateTrace\fR).

.PP

Calls to \fIproc\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 \fIproc\fR will occur,

one for each command.  The \fIcommand\fR string for each of these

trace calls will reflect only a single command, not the entire string

passed to Tcl_Eval.

.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.

.SH KEYWORDS

command, create, delete, interpreter, trace