FYI, WG14 will be considering N2688
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2688.pdf>, a paper
proposing to clarify how characters in character and string literals are
handled when the execution character set (literal encoding) does not
support representation for the source character (/basic-c-char/ or
/universal-character-name/ in C++) or escape sequence (presumably just
/simple-escape-sequence/ in C++, but the paper doesn't explicitly
exclude numeric escape sequences).

Tom.