A.4.2 Identifiers

C99 Identifier

ucn        ((\\u([[:xdigit:]]{4}))|(\\U([[:xdigit:]]{8})))
nondigit    [_[:alpha:]]
c99_id     ([_[:alpha:]]|{ucn})([_[:alnum:]]|{ucn})*

Technically, the above pattern does not encompass all possible C99 identifiers, since C99 allows for "implementation-defined" characters. In practice, C compilers follow the above pattern, with the addition of the ‘$’ character.

UTF-8 Encoded Unicode Code Point

[\x09\x0A\x0D\x20-\x7E]|[\xC2-\xDF][\x80-\xBF]|\xE0[\xA0-\xBF][\x80-\xBF]|[\xE1-\xEC\xEE\xEF]([\x80-\xBF]{2})|\xED[\x80-\x9F][\x80-\xBF]|\xF0[\x90-\xBF]([\x80-\xBF]{2})|[\xF1-\xF3]([\x80-\xBF]{3})|\xF4[\x80-\x8F]([\x80-\xBF]{2})