c++ - Clang 和 MSVC 为同一结构报告不同的 `sizeof`

Question

clang :3.8.0MSVC:19.00.24215.1 用于 x64

是什么导致了编译器之间的这种奇怪差异？ MSVC 报告 12，但 Clang 报告 8!这里的正确/预期行为是什么？标准对此有何规定？

enum class CodeCompletionDeclKind {};

struct SwiftSemanticToken {
  unsigned ByteOffset;
  unsigned Length : 24;
  CodeCompletionDeclKind Kind : 6;
  bool IsRef : 1;
  bool IsSystem : 1;
};
static_assert(sizeof(SwiftSemanticToken) == 8, "Too big");

int main()
{
    std::cout << "Hello, world!\n";
}

Answer 1

包含位字段的类对象的大小将由实现定义。

class.bit/1 :

...Allocation of bit-fields within a class object is implementation-defined. Alignment of bit-fields is implementation-defined. Bit-fields are packed into some addressable allocation unit. [ Note: Bit-fields straddle allocation units on some machines and not on others. Bit-fields are assigned right-to-left on some machines, left-to-right on others.  — end note ]