DN577060334

Subject: Re: Urgent: multiple return vals from FooObjCmd - DN [1]

David Gravereaux <davygrvy@bigfoot.com> - 24 Jan 2000 - comp.lang.tcl

 Dave O'Rourke <dorourke@ll.mit.edu> wrote:

 >To the extension writers in the audience...
 >
 >What is the best way to return multiple values to Tcl from a C command
 >procedure?  For example, suppose I have...
 >
 >int FooObjCmd(ClientData cd, Tcl_interp *interp, int objc, Tcl_Obj
 >*CONST objv[]);
 >
 >...which is intended to wrap another C function...
 >
 >int foo(int    index,     /* (in) index into data source */
 >        double startTime, /* (in) 1st time */
 >        double stopTime,  /* (in) last time */
 >        int    *nvals,    /* (out) number of values */
 >        double *times,    /* (out) the time array */
 >        double *values);  /* (out) the values array */
 >
 >So given this setup, what is the best way to get the data (the times
 >and values arrays) into Tcl?  Is there a way to return more than just
 >interp->result to Tcl?  Tcl_UpVar?  Tcl_LinkVar?  Is there a better way?
 > What am I missing?

 Here's my guess.  Please pardon an grossly neglected errors as i'm just typing
 this :)

 int
 FooObjCmd(ClientData cd, Tcl_interp *interp, int objc, Tcl_Obj *CONST objv[])
 {
   Tcl_Obj *resultPtr = Tcl_GetObjResult(interp);
   int index, nvals, i;
   double start, stop, times, values;

   if (Tcl_GetIntFromObj(interp, objv[1], &index) == TCL_ERROR) {
     /* error */
   }

   if (Tcl_GetDoubleFromObj(interp, objv[2], &index) == TCL_ERROR) {
     /* error */
   }

   if (Tcl_GetDoubleFromObj(interp, objv[3], &index) == TCL_ERROR) {
     /* error */
   }

   foo(index, start, stop, &nvals, &times, &values);

   for (i=0; i<nvals; i++)
   {
     Tcl_Obj *oData[2], *oList;

     oData[0] = Tcl_NewDoubleObj(times[i]);
     oData[1] = Tcl_NewDoubleObj(values[i]);
     oList = Tcl_NewListObj(2,oData);
     Tcl_ListObjAppendElement(interp, resultPtr, oList);
   }
   return TCL_OK;
 }

 That would return everything as a list within a list like this:
 {{time} {val}} {{time} {val}} {{time} {val}} {{time} {val}} ...

 set fooresult [foo $x $y $z]
 # time of third
 puts [lindex [lindex $fooresult 3] 0]
 # value of third
 puts [lindex [lindex $fooresult 3] 1]

 --
 * David Gravereaux *
 Tomahawk Software Group

 "Things should be as simple as possible, but not simpler." -- Albert E.