完成对象还是子对象？ [英] Complete object or subobject?

问题描述

C ++ 14标准说：

The C++14 Standard says:

子对象可以是成员子对象，基类子对象或数组元素。不是任何其他对象的子对象的对象称为完整对象。 （§1.8（2））

A subobject can be a member subobject, a base class subobject, or an array element. An object that is not subobject of any other object is called a complete object. (§1.8(2))

对我来说，'可以'是不是一个隐含的if除非'。为了提供一个例子，在下面的代码片段中，是指向一个完整的对象还是子对象？

It is not obvious to me whether the 'can be' is meant as an implicit 'if and only if'. To provide an example, in the snippet below, is r a reference to a complete object or to a subobject?

#include <iostream>
int main(){
  int i=2;
  unsigned char & r=reinterpret_cast<unsigned char&>(i);
  std::cout<<(int)r<<"\n";  
}

As r表示对象表示中的unsigned char，r应引用对象：

As r refers to an unsigned char in the object representation , r should refer to an object:

类型T的对象的对象表示是类型T的对象占用的N个unsigned char对象的序列，...（§3.9（4））

The object representation of an object of type T is the sequence of N unsigned char objects taken up by the object of type T, ... (§3.9(4))

---

非常清楚i的第一个字节是什么：
1）没有对象，
2）一个完整的对象，
3）一个子对象

---

edits: Could you please be very clear about what the first byte of i is: 1) no object at all, 2) a complete object, 3) a subobject

只有这三种可能性。

推荐答案

em>作为下列之一：成员子对象，基类子对象或数组元素。

The sentence is defining the term subobject as being one of: a member subobject, a base class subobject, or an array element.

您的代码段与子对象无关。 r 是引用，而不是对象。此外，它甚至不引用一个对象，它只是将 i 的第一个字节混淆。

Your snippet has nothing to do with subobjects. r is a reference, not an object. Moreover, it doesn't even refer to an object, it simply aliases the first byte of i.

[intro.object]：

From [intro.object]:

通过定义（3.1）创建对象 > / new>

An object is created by a definition (3.1), by a new-expression (5.3.4), when implicitly changing the active member of a union (9.3), or when a temporary object is created (4.4, 12.2).

i 是由定义创建的对象。因为 int 不是类或数组类型，它没有子对象。对象表示，构成 i 的存储的 unsigned char 的底层数组不是对象 - 在上述任何上下文中创建。定义对象表示的措辞是核心问题1701 （h / t TC ）。

i is an object created by a definition. As int is not a class or array type, it has no subobjects. The object representation, the underlying array of unsigned char that constitutes the storage of i, is not an object - it's not created in any of those contexts described above. The wording of the definition object representation is the subject of core issue 1701 (h/t T.C.).

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