Is assigning a type to an enum standard C?

Question

I have seen enum declarations like this:

enum ProgrammingLanguage: unsigned char {
    C = 0,
    CPlusPlus,
    Rust,
    Java,
    Javascript,
    Python
};

This only allocates one byte for this type. My question is, is this standard C or a GCC extension? Do I need to worry about portability if I decide to do this?

Answer 1

is this standard C

No, this is not a part of C language.

a GCC extension?

No, this is not a GCC extension in C language.

Do I need to worry about portability if I decide to do this?

You need to worry about compiling such code at all with any C compiler.

This is solely C++ feature.

Then it is a macOS feature. Compiling it in Xcode in a C file works

It is a clang extension .

Answer 2

Appendix A 6.7.2.2 defines an enum as:

(6.7.2.2) enum-specifier:
  enum identifier-opt { enumerator-list }
  enum identifier-opt { enumerator-list,}
  enum identifier