calling "c" from TCL

Pablo

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Feb 5, 2012, 3:42:30 PM2/5/12

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Hello,

To sum vectors i wrote a code like this; it is receiving 3 vectors
data1, data2, data3. The diference between data1 and data2 is returned
with Tcl_SetObjResult, but i would like modify data3, how can i modify
data3??

Thanks

#include <tcl.h>
#include <iostream>
using namespace std;

int obj_vecsub(ClientData clientData, Tcl_Interp *interp, int argc,
Tcl_Obj *const objv[]);
int obj_vecsub(ClientData clientData, Tcl_Interp *interp, int argc,
Tcl_Obj *const objv[])

{
if (argc != 3) {
Tcl_WrongNumArgs(interp, 1, objv, (char *)"?x? ?y?");
return TCL_ERROR;
}
int num1=0, num2=0, num3=0;
Tcl_Obj **data1, **data2, **data3;
if (Tcl_ListObjGetElements(interp, objv[1], &num1, &data1) !=
TCL_OK)
return TCL_ERROR;
if (Tcl_ListObjGetElements(interp, objv[2], &num2, &data2) !=
TCL_OK)
return TCL_ERROR;
if (Tcl_ListObjGetElements(interp, objv[3], &num2, &data3) !=
TCL_OK)
return TCL_ERROR;

if (num1 != num2) {
Tcl_SetResult(interp, (char *)"vecsub: two vectors don't have the
same size", TCL_STATIC);
return TCL_ERROR;
}

Tcl_Obj *tcl_result = Tcl_NewListObj(0, NULL);
Tcl_Obj *tcl_dummy = Tcl_NewListObj(0, NULL);
for (int i=0; i<num1; i++) {
double d1=0, d2=0, d3=77;
if (Tcl_GetDoubleFromObj(interp, data1[i], &d1) != TCL_OK) {
Tcl_SetResult(interp, (char *)"vecsub: non-numeric in first
argument", TCL_STATIC);
return TCL_ERROR;
}
if (Tcl_GetDoubleFromObj(interp, data2[i], &d2) != TCL_OK) {
Tcl_SetResult(interp, (char *)"vecsub: non-numeric in second
argument", TCL_STATIC);
return TCL_ERROR;
}
Tcl_ListObjAppendElement(interp, tcl_result, Tcl_NewDoubleObj(d1-
d2));
Tcl_ListObjAppendElement(interp, tcl_dummy,
Tcl_NewDoubleObj(d3));
}
Tcl_SetObjResult(interp, tcl_result);
return TCL_OK;
}

//int AddObjCmd(ClientData clientData, Tcl_Interp *interp,int objc,
Tcl_Obj *CONST objv[]);

extern "C" {
int Add_Init(Tcl_Interp *interp) ;
} // end extern "C" *

int Add_Init(Tcl_Interp *interp) {
/* Register the Add command */
Tcl_CreateObjCommand(interp, "vecsub", obj_vecsub,(ClientData) NULL,
(Tcl_CmdDeleteProc *) NULL);

/* Declare the package */
Tcl_PkgProvide(interp, "vecsub", "1.1");
return TCL_OK;
}

Alexandre Ferrieux

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Feb 5, 2012, 6:47:09 PM2/5/12

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On Feb 5, 9:42 pm, Pablo <pablodecasti...@gmail.com> wrote:
> Hello,
>
> To sum vectors i wrote a code like this; it is receiving 3 vectors
> data1, data2, data3. The diference between data1 and data2 is returned
> with Tcl_SetObjResult, but i would like modify data3, how can i modify
> data3??

Let the script level do that; just return the value:

set data3 [vecsub $data1 $data2]

Unless you have strong reasons (like modifying more than one var),
there's no point in bringing to the C level the equivalent of [upvar].

-Alex

Pablo

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Feb 6, 2012, 4:16:57 AM2/6/12

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On 6 feb, 00:47, Alexandre Ferrieux <alexandre.ferri...@gmail.com>
wrote:

Thanks Alex, but the idea is modify more than one var, the script is
working like;

set result [vecsub $dat1 $dat2 $dat3], and i would like modify $result
(it is doing calling the procedure) and $dat3

Thanks

Aric Bills

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Feb 6, 2012, 11:16:48 AM2/6/12

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If you want to modify a variable, you need to pass its name (rather
than its value) to your command. So, if you want to modify dat3, you'd
call your command like this:

set result [vecsub $dat1 $dat2 dat3]

If you need to get the value of the variable with that name, use
Tcl_ObjGetVar2. To set the variable, use Tcl_ObjSetVar2.

Alexandre Ferrieux

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Feb 6, 2012, 3:40:44 PM2/6/12

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You're not making it immediately obvious how this would modify several
variables...
Assuming you do it right (passing dat3 instead of $dat3, and
[upvar]ring it within the C function), what separate thing would the
function result hold ?

-Alex

Pablo

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Feb 7, 2012, 3:49:21 AM2/7/12

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Hi Aric,

I understand that "C" function transform dat3 in a variable for tcl,
is it?

Pablo

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Feb 7, 2012, 4:43:47 AM2/7/12

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Thanks Aric,

Your point is working perfectly, just adding to "c" function;
Tcl_ObjSetVar2( interp, objv[3], NULL, tcl_dummy, TCL_LEAVE_ERR_MSG );
and calling the script :
set c [vecsub $a $b d]

it is giving me $c and $d with modify values

Message has been deleted

Emiliano

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Feb 7, 2012, 11:23:59 AM2/7/12

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Two things worth noting:

1) You can return *two* vectors (list of lists) and use

lassign [vecsub $a $b] c d

and avoid accessing the variable from the C side.

2) your code is leaky; more specifically, you are not managing
Tcl_Obj's
reference count properly. Consider what happens with both tcl_result
and
tcl_dummy variables if Tcl_GetDoubleFromObj() fails.
See http://wiki.tcl.tk/1192 and http://wiki.tcl.tk/14880 for a
discussion
on this subject.

Regards
Emiliano

Pablo

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Feb 8, 2012, 11:43:31 AM2/8/12

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> Seehttp://wiki.tcl.tk/1192andhttp://wiki.tcl.tk/14880for a

> discussion
> on this subject.
>
> Regards
> Emiliano

Thanks Emiliano,

your point 1) is very useful.

Pablo