[[maybe_unused]]在枚举器上 [英] [[maybe_unused]] on enumerator

问题描述

查看 [[maybe_unused]] 的规范，它指出:

Looking at the specification of the [[maybe_unused]], it states:

出现在类，typedef，变量，非静态数据成员，函数，枚举或枚举器的声明中.如果编译器对未使用的实体发出警告，则对于声明为maybe_unused的任何实体，该警告将被抑制.

Appears in the declaration of a class, a typedef­, a variable, a non­static data member, a function, an enumeration, or an enumerator. If the compiler issues warnings on unused entities, that warning is suppressed for any entity declared maybe_unused.

正如上面提到的枚举器，我有点希望它有一个用例.我唯一想出的是-Wswitch警告，我在Clang，GCC和MSVC上尝试过.

As this mentions enumerator, I kinda expect it to have a use-case. As the only thing I could come up with is the -Wswitch warning, I tried it with Clang, GCC and MSVC.

enum A
{
    B,
    C [[maybe_unused]]
};

void f(A a)
{
    switch (a)
    {
        case B: break;
    }
}

所有3个编译器都给我以下警告的一种变化:

All 3 compilers give me a variation of following warning:

<source>:9:13: warning: enumeration value 'C' not handled in switch [-Wswitch]
    switch (a)
            ^

实时代码

这是使用此属性的有效用例吗，是否还有其他用例在此位置添加属性，或者这仅仅是无用的添加?

Is this a valid use case for using this attribute, are there other use cases for adding the attribute at this location or is this just a useless addition?

推荐答案

已为Clang记录了一个错误，并标记为已解决:

A bug was logged for Clang and marked as resolved: https://bugs.llvm.org/show_bug.cgi?id=36231

这似乎可以确认枚举值允许在没有警告的情况下在开关中丢失，以防被标记为[[maybe_unused]]

This seems to confirm that the enum value is allowed to be missing in a switch without warning in case it is tagged with [[maybe_unused]]

这篇关于[[maybe_unused]]在枚举器上的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！