是否有适用于方法的 offsetof 版本？

Question

给定结构：

struct Struct {
     int _a;

     int a () { return _a; }
};

可以得到 _a 与 offsetof( Struct, _a ) 的偏移量。

我将如何为 &Struct::a 之类的东西做同样的事情？

Answer 1

引自cppreference.com's page on the offsetof macro：（强调我的）

Given an object o of type type and static storage duration, o.member shall be an lvalue constant expression that refers to a subobject of o. Otherwise, the behavior is undefined. Particularly, if member is a static data member, a bit-field, or a member function, the behavior is undefined.

Answer 2

How would I go about doing the same for something like &Struct::a?

你不会也不能为成员函数做这样的事情，因为“偏移量”的概念对于成员函数没有意义。成员函数不像非静态成员变量那样存储在 class 实例中。

Answer 3

您似乎在寻找 pointers to members 函数：

int Struct::*m = &Struct::_a;
int (Struct::*f)() = &Struct::a;

用法类似于

Struct s;

s.*m = 42;
std::cout << (s.*f)() << std::endl;

Demo

是否有适用于方法的 offsetof 版本？

Is there a version of offsetof that applies to methods?

c++

reflection