How to convert a typedef enum into using enum in C++

Question

I'm trying to explore "using" in C++, and currently I would like to convert typedef into using.

For example,

typedef enum tag_EnumType : int {
    A,
    B,
    C,
} EnumType;

And I tried to convert it as following

using EnumType = enum tag_EnumType : int {
    A,
    B,
    C,
};

However, the compilation failed. Could anyone help? Thanks in advance.

The truth is, I'm working on a giant project. Some of typedef enum could be rewritten as using, but others couldn't. Does anyone know the reason? Is it related with namespace or sth?

You ask the reason why some can be rewritten, if you provide an example you may increase the chances for an answer — MatG, Jan 08 '22 at 07:39
@MatG thx for advice, it seems like the enum in namespace defined by using could not be rewritten, so I wonder whether it's because some special organism of C++ using — ghost, Jan 08 '22 at 07:53
I removed my answer since I didn't realize when answering that your code actually does work. As it is now, I would say the problem is non-reproducible without details. — user17732522, Jan 08 '22 at 08:28
Cannot reproduce e.g. here: https://www.tutorialspoint.com/compile_cpp_online.php — Yunnosch, Jan 08 '22 at 09:11
Why do you want to use `typedef` or `using` at all? Specific reason? Why don't you just write `enum EnumType : int { ... }`, which is the usual way in C++. Neither `typedef` nor `using` is needed. — Hajo Kirchhoff, Jan 08 '22 at 10:56
Well, I've found my mistake, I didn't give the enum a type name, and used it directly as a new type. Say `using EnumType = enum : int` and `void testFunc(EnumType e)`, after the type name has been added, `using EnumType = enum EnumType : int`, everything well well. — ghost, Jan 19 '22 at 08:22

score 2 · Answer 1 · edited Jan 08 '22 at 20:38

typedef enum is a C way of creating enums. If you want it the C++ way, you better write:

enum EnumType : int {
    A,
    B,
    C,
};

In C++11 and above, scoped enums are also available, that way you prevent name collisions.

 enum class EnumType : int {
    A,
    B,
    C,
};

using statements are for other typedefs, some examples:

using IntVector = std::vector<int>;
using Iterator = IntVector::Iterator;
using FuncPtr = int(*)(char, double);

How to convert a typedef enum into using enum in C++

1 Answers1