c++ - C++ 中的枚举类型是跨平台的吗？

Question

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Answer 1

In other words is sizeof(MyEnum) guaranteed to be the same size on all platforms?

您可以在 C++11 中设置显式类型(但在早期的 C++ 版本中不能):

enum class Drug : char {
    Cocaine,
    Cannabis,
    Crack
};

或

enum Sex : uint32_t {
    Male,
    Female,
    Other
};

在 enum 前面使用 class 会强制 Drug 的用户将其拼写为 Drug::Cocaine，对于声明前面没有 class 的枚举，拼写是可选的(Sex::Male 和 Female 都有效)。

2011 年之前的 C++es 黑客攻击包括以下内容，它们强制最小化:

enum Frob {
    ...
    FORCE_DWORD          = 0x7fffffff
};

在实践中看到，例如在 ReactOS 上 DirectX-SDK implementation .

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标准引用

7.2 Enumeration Declarations [dcl.enum]

[...]

§6: For an enumeration whose underlying type is not fixed, the underlying type is an integral type that can represent all the enumerator values defined in the enumeration. If no integral type can represent all the enumerator values, the enumeration is ill-formed. It is implementation-defined which integral type is used as the underlying type except that the underlying type shall not be larger than int unless the value of an enumerator cannot fit in an int or unsigned int. If the enumerator-list is empty, the underlying type is as if the enumeration had a single enumerator with value 0.