CODEWITHSUNDEEP
c++enumsconstantstypedef
Gorchestopher H
Gorchestopher H

Reputation: 1161

Is the declaration "const typedef enum" valid in C++?

I thought enums were static, what's the point of a const enum?

For example:

const typedef enum
{
    NORMAL_FUN = 1,
    GREAT_FUN = 2,
    TERRIBLE_FUN = 3,
} Annoying;

I have had an old program dropped on my head that I am being forced to work with (from an equipment manufacturer), and I keep coming across enums being defined with const typedef enum.

Now, I am used to C#, so I don't fully understand all the C++ trickery that goes on, but this case appears to be straightforward.

From the coding of the program it would appear that variables that are of type Annoying are meant to be changed, everywhere, all the time.

They aren't meant to be constant. Long story short, the compiler doesn't like it.

This sample was written back sometime prior to 2010, so this could be some kind of version difference, but what did/does const typedef enum even mean?

Upvotes: 0

Views: 687

Answers (3)

Bathsheba
Bathsheba

Reputation: 234635

Writing

typedef enum
{
    NORMAL_FUN = 1,
    GREAT_FUN = 2,
    TERRIBLE_FUN = 3,
} Annoying;

has the advantage of the enum working nicely in C too, which handles typedef by introducing Annoying into the typedef namespace. So the provider of the enum declaration could be also targetting C.

Using the const qualifier means that you cannot write code like

Annoying foo = NORMAL_FUN;
foo = GREAT_FUN; // this will fail as `foo` is a `const` type.

Upvotes: 1

user743382
user743382

Reputation:

const typedef Type def; and typedef const Type def; mean the same thing, and have for many years. There's nothing special about the case where Type is an enum definition, and you can see it too in:

const typedef int const_int;
const_int i = 3;
i = 4; // error

Upvotes: 3

Some programmer dude
Some programmer dude

Reputation: 409136

That makes the type-alias Annoying constant, so all variables declared with that type-aliases are constant:

Annoying a = NORMAL_FUN;
a = GREAT_FUN;  // Failure, trying to change a constant variable

Upvotes: 7

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