如果它们是多态类型，并且只需要一个指向导出类型的指针，请使用 dynamic_cast ：

If they are polymorphic types and you only need a pointer to the derived type use dynamic_cast:

Derived *derivedPointer = dynamic_cast<Derived*>(basePointer.get());

如果它们不是多态类型，只需要一个指向导出类型的指针。 static_cast 并希望获得***效果：

If they are not polymorphic types only need a pointer to the derived type use static_cast and hope for the best:

Derived *derivedPointer = static_cast<Derived*>(basePointer.get());

如果您需要转换 unique_ptr 多态类型：

If you need to convert a unique_ptr containing a polymorphic type:

Derived *tmp = dynamic_cast<Derived*>(basePointer.get());
std::unique_ptr<Derived> derivedPointer;
if(tmp != nullptr)
{
    basePointer.release();
    derivedPointer.reset(tmp);
}

如果您需要转换 unique_ptr 包含非多态类型：

If you need to convert unique_ptr containing a non-polymorphic type:

std::unique_ptr<Derived>
    derivedPointer(static_cast<Derived*>(basePointer.release()));