NULL pointer with boost::shared_ptr?

Question

What\'s the equivalent to the following:

std::vector vec;
vec.push_back(NULL);

when dealing with boost::shared_ptr

Answer 1

Well, this is legal:

shared_ptr foo;  /* don't assign */

And in this state, it doesn't point to anything. You can even test this property:

if (foo) {
    // it points to something
} else {
    // no it doesn't
}

So why not do this:

std::vector < shared_ptr > vec;
vec.push_back (shared_ptr);   // push an unassigned one