笔试面试 下列代码的输出是什么? #include <iostream> class Base { public: virtual void foo() { std::cout << “Base::foo()” << std::endl; } }; class Derived : public Base { public: void foo() override { std::cout << “Derived::foo()” << std::endl; } }; int main() { Derived d; Base &r = d; r.foo(); return 0; }