c++ - auto_ptr 和 dynamic_pointer_cast

Question

如果我想将 dynamic_cast 与 shared_ptr 一起使用，我可以使用 dynamic_pointer_cast。如果我想转换 auto_ptr，我该用什么？我假设如下所示。

struct B : A { };
...
auto_ptr<A> base( ... );
auto_ptr<B> derive = dynamic_pointer_cast<B>(base);

我正在为 shared_ptr 使用 boost

Answer 1

auto_ptr<A> base( ... );
if(B* query = dynamic_cast<B>(base.get())) {
    // take ownership
    base.release();
    auto_ptr<B> derived(query);

    // use and/or pass derived around here
    // ...
} else {
    // no dice: leave base as owner
}

---

既然你已经这样做了，那就重构它，把它放在你选择的命名空间中，然后收工:

// Postcondition:
// where r is the returned pointer and p == from.get()
// EITHER r == 0 AND from.get() == p
// OR r.get() == dynamic_cast<To>(p) AND from == 0
template<typename To, typename From>
std::auto_ptr<To>
dynamic_pointer_cast(std::auto_ptr<From>& from)
{
    To* query = dynamic_cast<To>(from.get());
    return query ? from.release(), query : 0;
}