[c/c++]判断一个字符串是不是UTF-8字符串

#define CHECK_LENGTH 20       //检查是否为utf8编码时所检查的字符长度   

int is_utf8_string(char *utf)
    {
        int length = strlen(utf);
        ;
        ;  

        if ( length > CHECK_LENGTH )  //只取前面特定长度的字符来验证即可
        {
            length = CHECK_LENGTH;
        }  

        for ( ; i < length; i ++ )
        {
             )
            {
                ) ==  )         //0xxx xxxx
                {
                    continue;
                }
                else if ( (utf[i] & 0xE0) == 0xC0 ) //110x xxxx
                {
                    check_sub = ;
                }
                else if ( (utf[i] & 0xF0) == 0xE0 ) //1110 xxxx
                {
                    check_sub = ;
                }
                else if ( (utf[i] & 0xF8) == 0xF0 ) //1111 0xxx
                {
                    check_sub = ;
                }
                else if ( (utf[i] & 0xFC) == 0xF8 ) //1111 10xx
                {
                    check_sub = ;
                }
                else if ( (utf[i] & 0xFE) == 0xFC ) //1111 110x
                {
                    check_sub = ;
                }
                else
                {
                    ;
                }
            }
            else
            {
                if ( (utf[i] & 0xC0) != 0x80 )
                {
                    ;
                }
                check_sub --;
            }
        }
        ;
    }