bool MainWindow::isUtf8File(QIODevice *file)
{
    const int testSize = 1024;
    char str[testSize];///
    int size = file->peek(str, testSize);

//    char buf[3];
//    if (f->peek(buf, sizeof(buf)) == sizeof(buf))
//        return (buf[0] == 0xEF && buf[1] == 0xBB && buf[2] == 0xBF);

    int encodingBytesCount = 0;
    bool allTextsAreASCIIChars = true;

    for (int i = 0; i < size; ++i){
        char current = str[i];

        if ((current & 0x80) == 0x80)
            allTextsAreASCIIChars = false;

        // First byte
        if (encodingBytesCount == 0){
            if ((current & 0x80) == 0)
                continue;// ASCII chars, from 0x00-0x7F

            if ((current & 0xC0) == 0xC0){
                encodingBytesCount = 1;
                current <<= 2;
                // More than two bytes used to encoding a unicode char.
                // Calculate the real length.
                while ((current & 0x80) == 0x80){
                    current <<= 1;
                    ++encodingBytesCount;
                }
            }else{
                // Invalid bits structure for UTF8 encoding rule.
                return false;
            }
        }else{
            // Following bytes, must start with 10.
            if ((current & 0xC0) == 0x80)
                --encodingBytesCount;
            else
                return false;
        }
    }

//    if(encodingBytesCount != 0)
//    {
//        // Invalid bits structure for UTF8 encoding rule.
//        // Wrong following bytes count.
//        return false;
//    }

    // Although UTF8 supports encoding for ASCII chars, we regard as a input stream, whose contents are all ASCII as default encoding.
    return !allTextsAreASCIIChars;
}