如果你用的是WINCC6.0以下的版本！
那就用如下的C程序了：

#define GetObject GetObject

__object *pdl=NULL;
__object *pic=NULL;
__object *obj=NULL;
long pos;

pdl = __object_create("PDLRuntime");
pic=pdl->GetPicture(lpszPictureName);
obj=pic->GetObject("SliderCtrl");
pos=obj->Position;

SetTagDWord("tag",pos);

__object_delete(obj);
__object_delete(pic);
__object_delete(pdl);