C++ : What is happening when a non-overridden calls a overridden method?

Question

被调用的覆盖方法的版本取决于 如果您关心“通过”基类或“通过”派生类调用函数。但是，我发现如果我调用一个非重写方法，并且重写方法调用一些被重写的函数，那么基类版本仍然被调用，即使我通过指针访问实例到派生类。有人可以解释为什么会这样吗？

代码:

class Base {
public:
    void display() {
        foo();
    }
    void foo() {
        cout << "Base.foo()" << endl;
    }
};

class Derived : public Base {
public:
    void foo() {
        cout << "Derived.foo()" << endl;
    }
};

int main() {
    Derived* derived = new Derived();
    derived->display();
    while (true) {}
}

Answer 1

the base class version is still called, even though I am accessing the instance through pointer to the derived class. Could someone explain why this happens?

虽然您通过指向派生类的指针调用方法，但您的方法不是虚拟的，因此使用静态分派(dispatch)，所以 Base::display() 调用 Base::foo() 直接，即使它在子类中被覆盖。要实现您想要的行为，您必须使用动态调度，即将您的方法标记为 virtual。

class Base {
public:
    void display() {
        foo();
        bar();
    }
    void foo() {
        cout << "Base.foo()" << endl;
    }
    virtual void bar() {
        cout << "Base.bar()" << endl;
    }
};

class Derived : public Base {
public:
    void foo() {
        cout << "Derived.foo()" << endl;
    }
    virtual void bar() {
        cout << "Derived.bar()" << endl;
    }
};

int main() {
    Derived* derived = new Derived();
    derived->display();
}

输出:

Base.foo()
Derived.bar()