These statements test whether the field identified by fid is a global variable object. If it is, its value is set to another global variable object:

fid = session -> GetGlobalVarID("obj2_gvar");
   if (session -> IsGlobalVarObject(fid))
   {
      obj_val = session -> GetObjectGlobalVar(fid,
         isNull);
      cls = session -> GetClass(obj_val);
      fid = session -> GetFieldID(cls, "text");
      s_val = session -> GetStringField(obj_val, fid,
         isNull);
      mystr = session -> GetString(s_val);
      // Set the value of obj2_gvar to obj1_gvar
      fid = session -> GetGlobalVarID("obj1_gvar");
      session -> SetObjectGlobalVar(fid, obj_val);
   }