通过指向其基址的指针删除POD对象是否安全？ [英] Is it safe to delete a POD object by a pointer to its base?

问题描述

实际上，我正在考虑简单的可破坏对象，不仅仅是关于 POD （我不确定POD可以有基类）。

Actually I am thinking about trivially destructible objects, not only about POD (I am not sure POD can have base class).

当我阅读这个解释

When I read this explanation for is_trivially_destructible from cppreference I notice this:

可被重复使用的可破坏的对象的存储可以被重用。调用析构函数。

Storage occupied by trivially destructible objects may be reused without calling the destructor.

所以，这是安全的：

struct A {
  int a;
};
struct B : A {
  int b;
};
int main() {
  A* a = new B;
  delete a;
}

B ::〜B c $ c>不会被调用 - 和AFAIK（请更正，如果我错了）整个内存将被释放。 B ::〜B（）肯定是微不足道的。

我知道这个代码气味不好，问题只是关于这个代码的安全性...

I know this code smells badly, but my question is only about safeness of this code...

推荐答案

不，这是不允许的。 [expr.delete] / p3，emphasis mine：

No, this is not allowed. [expr.delete]/p3, emphasis mine:

在第一个选项要被删除的
对象的静态类型不同于其动态类型，静态
类型应该是被删除的
的对象的动态类型的基类;静态类型应具有虚拟析构函数或
行为未定义。

In the first alternative (delete object), if the static type of the object to be deleted is different from its dynamic type, the static type shall be a base class of the dynamic type of the object to be deleted and the static type shall have a virtual destructor or the behavior is undefined.

事实上，委员会最近拒绝 通过指针到底层明确定义删除POD的建议。

In fact, the committee fairly recently rejected a proposal to make deleting a POD via a pointer-to-base well-defined.

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