该标准在 [basic.align]/1 :

对象类型具有对齐要求(3.9.1、3.9.2)，这些要求放在 对该类型的对象可能位于的地址的限制 已分配. 对齐方式是实现定义的整数值 代表连续地址之间的字节数 可以分配给定的对象.对象类型强制对齐 对该类型的每个物体的要求；可以更严格地对齐 使用对齐说明符(7.6.2)请求.

Object types have alignment requirements (3.9.1, 3.9.2) which place restrictions on the addresses at which an object of that type may be allocated. An alignment is an implementation-defined integer value representing the number of bytes between successive addresses at which a given object can be allocated. An object type imposes an alignment requirement on every object of that type; stricter alignment can be requested using the alignment specifier (7.6.2).

此外， [basic.compound]/3 提到:

指针类型的值表示形式是实现定义的. 指向 layout-compatible类型的指针应具有相同的值 表示和对齐要求(6.11). [注意:指向 过度对齐的类型(6.11)没有特殊的表示形式，但是它们的 有效值范围受扩展对齐方式的限制 要求].

The value representation of pointer types is implementation-defined. Pointers to layout-compatible types shall have the same value representation and alignment requirements (6.11). [Note: Pointers to over-aligned types (6.11) have no special representation, but their range of valid values is restricted by the extended alignment requirement].

因此，可以保证与布局兼容的类型具有相同的对齐方式.

As a result, there is a guarantee that layout-compatible types have the same alignment.

struct { T m; }和T与布局不兼容.

如指出的那样

As pointed here, in order for two elements to be layout compatible then they both have to be standard-layout types, and their non-static data members must occur with the same types and in the same order.

struct { T m; }仅包含T，但是T是T，因此它不能包含T作为其第一个非静态数据成员.

struct { T m; } contains just a T, but T is a T so it cannot contain a T as its first non-static data member.