判断

使用以下函数可以判断：

bool utf8_check_is_valid(const string& string)
{
    int c,i,ix,n,j;
    for (i=0, ix=string.length(); i < ix; i++)
    {
        c = (unsigned char) string[i];
        //if (c == 0x09 || c == 0x0a || c == 0x0d || (0x20 <= c && c <= 0x7e) ) n = 0; // is_printable_ascii
        if (0x00 <= c && c <= 0x7f) n=0; // 0bbbbbbb
        else if ((c & 0xE0) == 0xC0) n=1; // 110bbbbb
        else if ( c==0xed && i<(ix-1) && ((unsigned char)string[i + 1] & 0xa0)==0xa0) return false; //U+d800 to U+dfff
        else if ((c & 0xF0) == 0xE0) n = 2; // 1110bbbb
        else if ((c & 0xF8) == 0xF0) n = 3; // 11110bbb
        //else if (($c & 0xFC) == 0xF8) n = 4; // 111110bb //byte 5, unnecessary in 4 byte UTF-8
        //else if (($c & 0xFE) == 0xFC) n = 5; // 1111110b //byte 6, unnecessary in 4 byte UTF-8
        else return false;
        for (j=0; j < n && i < ix; j++) { // n bytes matching 10bbbbbb follow ?
            if ((++i == ix) || (( (unsigned char)string[i] & 0xC0) != 0x80))
                return false;
        }
        //if (j != n) return false; // not enough bytes for this UTF-8 encoded character
    }
    return true;
}

END