c++ - 指向对象生命周期之外分配的内存的指针是 "invalid pointer[s]"还是 "pointer[s] to an object"？

Question

C++17(草案 N4659)[basic.compound]/3说:

Every value of pointer type is one of the following:

• a pointer to an object or function (the pointer is said to point to the object or function), or

• a pointer past the end of an object ([expr.add]), or

• the null pointer value ([conv.ptr]) for that type, or

• an invalid pointer value.

指向对象生命周期之外已分配内存的指针属于这些类别中的哪一个，特别是 //(1) 到 //处的 a 值以下程序中的 (3) 和 b 位于 //(4) 处？

#include<new>
#include<algorithm>

struct S {
    ~S() { /* Non-trivial destructor */ }
};

struct T {
    ~T() { /* Non-trivial destructor */ }
};

int main() {
    void* a = operator new(std::max(sizeof(S), sizeof(T)));
    // (1)
    a = new(a) S;
    static_cast<S*>(a)->~S();
    // (2)
    a = new(a) T;
    static_cast<T*>(a)->~T();
    // (3)
    operator delete(a);   

    void* b = operator new(42);
    // (4)
    operator delete(b);
}

<小时/>

根据我的理解，指针值在释放时变得无效，而不是在对象的生命周期结束时，但如果指针值是“指向对象的指针”，则>他们指向哪个物体？

Answer 1

To which of these categories belong pointers to allocated memory outside the lifetime of objects, specifically the values of a at // (1) through // (3) and b at // (4) in the following program?

从分配函数返回的指针值(a at //(1) 和 b at //(4)) 目前尚未指定，几乎不可能根据 [basic.compound]/3 中的分类法对它们进行分类，请参阅 https://groups.google.com/a/isocpp.org/d/msg/std-discussion/4NQawIytVzM/eMKo2AJ9BwAJ

In my understanding a pointer value becomes invalid when deallocated, not when the life time of an object ends, but if the pointer values are "pointer[s] to an object", to which object do they point?

当对象还活着时，指向它们所指向的对象。