Tcl API how to get a list from Tcl - c++

Question

Tcl 8.4
In my Tcl script:
set foo1 false
set foo2 "yes"
set foo3 [list item1 item2 item3]
There's a API to get scalars like foo1 or foo2. Eg: Tcl_GetVar(tcl_interp, string("foo1").c_str(), flags). I was wondering if there's any API to get list (like foo3) from Tcl?

Answer 1

It's a two-stage thing. You first fetch the value with one of the Tcl_GetVar family of functions, then you get the pieces of the list that you're interested in (with Tcl_SplitList or Tcl_ListObjGetElements, normally).
As a more concrete example:
////// FETCH FROM VARIABLE //////
// The NULL is conventional when you're dealing with scalar variable,
// and the 0 could be TCL_GLOBAL_ONLY or
Tcl_Obj *theList = Tcl_GetVar2Ex(interp, string("foo1").c_str(), NULL, TCL_LEAVE_ERR_MSG);
if (theList == NULL) {
// Was an error; message in interpreter result...
}
////// EXTRACT ELEMENTS //////
int objc;
Tcl_Obj **objv;
if (Tcl_ListObjGetElements(interp, theList, &objc, &objv) == TCL_ERROR) {
// Not a list! error message in interpreter result...
}
////// WORK WITH VALUES //////
for (int i=0 ; i<objc ; i++) {
const char *value = Tcl_GetString(objv[i]);
// Whatever...
}

Answer 2

I'm not sure, but Tcl_ListObjGetElements looks like what you want. Or, alternatively, Tcl_ObjGetVar2 would return a Tcl_Obj which you could then manipulate using the rest of the Tcl API for working with list objects.

Answer 3

Hi i have found this useful link containing an example for dealing the list:
Reference:: https://www.tcl.tk/man/tclx8.2/TclCommandWriting.3.html
int Tcl_LreverseObjCmd(notUsed, interp, objc, objv)
ClientData notUsed; /* Not used. */
Tcl_Interp *interp; /* Current interpreter. */
int objc; /* Number of arguments. */
Tcl_Obj **obj; /* Argument strings. */
{
int listObjc, lowListIndex, hiListIndex;
Tcl_Obj **listObjv;
char *temp, *resultList;
Tcl_Obj **newListObjv;
/* Verify argument count. Since we take only one argument, argument
* count must be 2 (command plus one argument).
*/
if (objc != 2)
return TclX_WrongArgs (interp, objv [0], "list");
/* Create an object to handle the new list we're creating */
newListObjv = Tcl_NewObj();
/* Crack the list at objv[1] into its own count and array of object
* pointers.
*/
if (Tcl_ListObjGetElements (interp, objv[1], &listObjc, &listObjv) != TCL_OK) {
return TCL_ERROR;
}
/* For each element in the source list from last to first, append an
* element to the new list.
*/
for (listIndex = listObjc - 1; listIndex >= 0; listIndex--) {
Tcl_ListObjAppendElement (interp, newListObjv, listObjv[listIndex]);
}
FIX: NEED TO RETURN THE LIST.
return TCL_OK;
}