c - 在 [C] 中将 `enum` 转换为其他 `enum` 是否有效？

Question

我有两个枚举。

enum A { A1=1, A2=2 }

enum B { B1=1, B2=2 }

这是否符合 C 标准？

A a = A1;
B b = a;

(用 Clang 编译得很好，但我不能确定这是标准行为还是扩展行为)

Answer 1

按照标准它是有效的，但 C99 规范提到某些实现可能会产生警告:

An implementation may generate warnings in many situations, none of which are specified as part of this International Standard. The following are a few of the more common situations.

• A value is given to an object of an enumerated type other than by assignment of an enumeration constant that is a member of that type, or an enumeration variable that has the same type, or the value of a function that returns the same enumerated type (6.7.2.2).