https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67224
--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- There is no "C99" character set in glibc libiconv (after all, it's not a character set at all). Converting extended characters to UCNs like that would in any case be correct for C++ (provided you also convert $ ` @ and control characters other than those in the basic source character set) but not for C - but for C++, it would be necessary to keep track of the conversions to revert them in raw string literals. This requirement to revert such conversions in raw string literals (in C++14, see 2.5 [lex.pptoken] paragraph 3: "Between the initial and final double quote characters of the raw string, any transformations performed in phases 1 and 2 (trigraphs, universal-character-names, and line splicing) are reverted; this reversion shall apply before any d-char, r-char, or delimiting parenthesis is identified.") renders such an approach non-viable (it would break things that currently work); the conversions to UCNs have to take place within cpplib, not through an external iconv conversion. Note that cpplib identifier spelling preservation is now implemented <https://gcc.gnu.org/ml/gcc-patches/2014-11/msg00548.html>, which adds other ways in which it should be visible whether an identifier was represented with UTF-8 or UCNs.
