结构中的数组是否会出现 Aliasing/Alignment 问题？

Question

如果我们在结构中有一个数组：

struct Names
{
   uint8 fileId;
   uint8 name[50];
};

然后我们尝试将数组中的 uint16 分配给 uint16 变量，例如：

uint16 someName = *((uint16 *)&NamesObj.name[21]);

这会违反别名 rule/alignment 规则并导致未定义的行为吗？

Answer 1

是的，这违反了 C 规则。 name 中的对象是 uint8（大概是一些无符号的 8 位整数类型），它们通过指向 uint16（大概是一些 16 位整数类型）的指针访问。

2011 C 标准的相关部分，来自 N1570 草案，是 6.5 7:

An object shall have its stored value accessed only by an lvalue expression that has one of the following types:

— a type compatible with the effective type of the object,

— a qualified version of a type compatible with the effective type of the object,

— a type that is the signed or unsigned type corresponding to the effective type of the object,

— a type that is the signed or unsigned type corresponding to a qualified version of the effective type of the object,

— an aggregate or union type that includes one of the aforementioned types among its members (including, recursively, a member of a subaggregate or contained union), or

— a character type.

类型 uint16 是其中的 none 个。

结构中的数组是否会出现 Aliasing/Alignment 问题？

Does Aliasing/Alignment issues occur for an Array within a Structure?

c

structure

strict-aliasing