Convert containers via constructor

Convert containers via constructor

Suppose I have classes
class A {
//...
};
struct B {
explicit B(const A&);
//...
};
and I have a container of A's, from which I would like to construct a
container of B's. What is an idiomatic way to do this in c++ 03?
Tried and failed:
std::vector<A> source = fillSourceObjects();
std::vector<B> target;
// 1) won't compile; presumably I need a static helper function,
// but I would like to avoid that
std::transform(source.begin(), source.end(), std::back_inserter(target), B);
std::transform(source.begin(), source.end(), std::back_inserter(target),
B::B);
// 2) won't compile; "... error: no match for 'operator=' in '* __result =
*__first'
std::copy(source.begin(), source.end(), target.begin());