我可以在 C++ 中使用非 ASCII 字符创建变量名吗？

Question

I write in c++ since 2010.

I've just accidentally inputed “й“ letter in my code, hover mouse on it to remove, and noticed that Visual Studio just says there is no variable “й“.

I wrote int й = 1; and it just compiled!

What did I miss?

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Bet, it's probably features of c++ 11,14 or something like this.

Answer 1

Here's what The Standard says ([lex.phases]):

Physical source file characters are mapped, in an implementation-defined manner, to the basic source character set (introducing new-line characters for end-of-line indicators) if necessary. The set of physical source file characters accepted is implementation-defined.

So your particular implementation supports that, but it's not guaranteed to be portable to any other implementation.

Answer 2

If you look at Annex E of this paper , you can see that there are certain unicode ranges allowed to be variable names. These ranges include:

00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6, 00D8-00F6, 00F8-00FF 0100-167F, 1681-180D, 180F-1FFF 200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F 2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF 3004-3007, 3021-302F, 3031-303F 3040-D7FF F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD 10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD, 60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD, B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD

Answer 3

Well, seems there is no restriction on the Unicode character using to define an identifier according to MSDN

struct テスト         // Japanese     'test'
{
void トスト() {}  // Japanese      'toast'
};

 int main() {
テスト \u30D1\u30F3;  // Japanese      パン 'bread' in UCN form
パン.トスト();        // compiler      recognizes UCN or literal form
 }

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I am disappointed that cplusplus.com has no word about this.