C++ iterate or split UTF-8 string into array of symbols?

Question

Searching for a platform- and 3rd-party-library- independent way of iterating UTF-8 string or splitting it into array of UTF-8 symbols.

Please post a code snippet.

Answer 1

Off the cuff:

// Return length of s converted. On success return should equal s.length().
// On error return points to the character where decoding failed.
// Remember to check the success flag since decoding errors could occur at
// the end of the string
int convert(std::vector& u, const std::string& s, bool& success) {
    success = false;
    int cp = 0;
    int runlen = 0;
    for (std::string::const_iterator it = s.begin(), end = s.end(); it != end; ++it) {
        int ch = static_cast(*it);
        if (runlen > 0) {
            if ((ch & 0xc0 != 0x80) || cp == 0) return it-s.begin();
            cp = (cp << 6) + (ch & 0x3f);
            if (--runlen == 0) {
                u.push_back(cp);
                cp = 0;
            }
        }
        else if (cp == 0) {
            if (ch < 0x80)      { u.push_back(ch); }
            else if (ch > 0xf8) return it-s.begin();
            else if (ch > 0xf0) { cp = ch & 7; runlen = 3; }
            else if (ch > 0xe0) { cp = ch & 0xf; runlen = 2; }
            else if (ch > 0xc0) { cp = ch & 0x1f; runlen = 1; }
            else return it-s.begin(); // stop on error
        }
        else return it-s.begin();
    }
    success = runlen == 0; // verify we are between codepoints
    return s.length();
}