[Boost-users] how can I return a 'null' smart pointer?

Hi, Can you please tell me how can I return a 'null' smart pointer? typedef shared_ptr<MyA> MyAPtr; typedef vector<MyAPtr> MyAVector; For example,I have this code, which return NULL in an error situation: MyAPtr myfunction(MyAVector& v, int size) { if (index < v.size()) { return v[index]; } else { // how can I return NULL here? } } How can I achieve that when I use boost smart pointer? Thank you for any tip.