Re: [MACTCL] [Q] Tcl_SetObj ???

[Neil M. <ne...@cs...>]

Michael Norton (mnorton) wrote:
> hi,
>  
> Does a C extension library exist for setting a Tcl Obj?
> For instance,
>  
> result = Tcl_ListObjGetElements(interp, listPtr, &len, &elemPtrs);
> :
> strPtr = Tcl_GetString(elemPtrs[0]);
>  
> Now I want to write back a new value to elemPtrs[0]. Can I do that? How 
> do I do that?
> Is there a Tcl_SetObj? (probably).

You want Tcl_ListObjReplace, I suspect. Tcl_Obj's are conceptually 
immutable (they represent values), so you are only allowed to update 
them if you hold the only reference. The Tcl_Set<type>Obj functions will 
abort (panic) if you call them with a Tcl_Obj with refcount > 1. So, 
unless you know that you will always have a unique reference to the 
object, then you need code like the following:

int result;

if (Tcl_IsShared(listPtr)) {
     // Make a copy
     listPtr = Tcl_DuplicateObj(listPtr);
}
result = Tcl_ListObjReplace(interp, listPtr, 0, 0, 1, &newValuePtr);
if (result != TCL_OK) { return TCL_ERROR; }
Tcl_SetObjResult(interp, listPtr);
return TCL_OK;

See the Tcl_DuplicateObj manpage for more information.

-- Neil