Why would an enum declaration be marked const?

Question

I saw this construct in the project I work:

const enum SomeEnum
{
    val0,
    val1,
    val2
};

What is the purpose of const here?

I believe this is invalid C++ code but Visual Studio does accept it (GCC doesn't). In addition Visual Studio also accepts `const class A { /* ... */ };`. — Cassio Neri, Jul 23 '13 at 09:31
Related MSVC bug: [MSVC const enum type](http://stackoverflow.com/q/14923403) — Cody Gray - on strike, Jul 23 '13 at 09:45

score 20 · Accepted Answer · answered Jul 23 '13 at 08:48

Nothing at all. Actually, according to G++ it is a compiler error:

error: qualifiers can only be specified for objects and functions

However, in C it is allowed, but useless. GCC says:

warning: useless type qualifier in empty declaration

The issue is that const only applies to objects (variables) and member functions, but not to basic types.

score 15 · Answer 2 · answered Jul 23 '13 at 08:46

15

It doesn't make a difference in your code, but it would in this case:

const enum SomeEnum
{
    val0,
    val1,
    val2
} VAL0 = val0;

Here, VAL0 would be a const variable (with the value val0). TBH though, it isn't of much use.

answered Jul 23 '13 at 08:46

Luchian Grigore

7

I think it *does* make difference: "it shouldn't compile". – Nawaz Jul 23 '13 at 08:51
@Nawaz I saw that it didn't compile, however that might just be the compiler. Is there anything in the rules against it? I've seen compilers both accepting and rejecting `static struct X{};`. – Luchian Grigore Jul 23 '13 at 08:52
1

Same thing as doing `const int;` or similar I would imagine. – chris Jul 23 '13 at 08:53
In C++, expressions can be `const` or `volatile`, not the types. It is like writing `const int;` as @chris said. – Nawaz Jul 23 '13 at 08:57
@Nawaz I agree it doesn't make sense, what I'm saying is I don't think this is addressed directly (that I know of), so it might be up to the compiler. – Luchian Grigore Jul 23 '13 at 09:01
in vc++ 2012 i am able to do ++VAL0; I don't understand how his const is undergoing to ++. Can anyone help me to understand ? – mahendiran.b Apr 22 '15 at 13:49

2 Answers2