c++ - 为什么删除一个没有virtual dtor的类如果它继承了一个有virtual dtor的类就可以了

Question

考虑下面的代码

#include <cstdio>
#include <memory>

struct Base1
{
    Base1() = default;
    virtual ~Base1() = default;
    //~Base1() = default;
};

struct Base2 : public Base1
{
    Base2()
    {
        printf("%s:%d:%s\n", __FILE__, __LINE__, __func__);
    }
    ~Base2() // non-virtual destructor
    {
        printf("%s:%d:%s\n", __FILE__, __LINE__, __func__);
    }
};

struct Derive : public Base2
{
    Derive()
    {
        printf("%s:%d:%s\n", __FILE__, __LINE__, __func__);
    }
    ~Derive()
    {
        printf("%s:%d:%s\n", __FILE__, __LINE__, __func__);
    }
};

int main()
{
    std::unique_ptr<Base2> d = std::make_unique<Derive>();
    return 0;
}

类(class)Base2没有虚拟析构函数，但它继承了 Base1它有一个虚拟析构函数。

代码std::unique_ptr<Base2> d = std::make_unique<Derive>();正在尝试删除 Base2在 Derive 类型的对象上，我只期待 Base2的 dtor 被调用，但不是 Derive .

但实际上它工作正常:

main.cpp:15:Base2
main.cpp:27:Derive
main.cpp:31:~Derive
main.cpp:19:~Base2

所以看起来只要“真正的”基类(这里是Base1)有虚拟dtor，所有的继承类都不需要有虚拟dtor，是吗？如果是，我在哪里可以找到这方面的相关文件？

Answer 1

是的，如果一个类有一个基类，其 destructor被声明为virtual，它的析构函数也将是virtual；无论是否显式声明它为 virtual。

Even though destructors are not inherited, if a base class declares its destructor virtual, the derived destructor always overrides it. This makes it possible to delete dynamically allocated objects of polymorphic type through pointers to base.

class Base {
 public:
    virtual ~Base() { /* releases Base's resources */ }
};

class Derived : public Base {
    ~Derived() { /* releases Derived's resources */ }
};

int main()
{
    Base* b = new Derived;
    delete b; // Makes a virtual function call to Base::~Base()
              // since it is virtual, it calls Derived::~Derived() which can
              // release resources of the derived class, and then calls
              // Base::~Base() following the usual order of destruction
}

来自标准，[class.dtor]/13

(强调我的)

A prospective destructor can be declared virtual ([class.virtual]) or pure virtual ([class.abstract]). If the destructor of a class is virtual and any objects of that class or any derived class are created in the program, the destructor shall be defined. If a class has a base class with a virtual destructor, its destructor (whether user- or implicitly-declared) is virtual.