How to do Xor operation with QByteArray and copy it to another QBytearray[solved]

vishnu

I have received Hex data from the socket. Now I want to update the GUI based on the data changed. So my logic is to perform XOR operation between newData and oldData so that I get the Byte which is changed .Then again i parse through that byte to get which bit is changed.Then I want to send byte index,bit index and value to QML through signal(byteindex,bitindex,value). As the first step to compared each byte I am getting error.Also Can you please tell me how to copy one Qbytearray to another one( receviedData to m_oldData).Can any one please help me.Thanks

QByteArray m_oldData(68,'\0');//How to Initialize all bytes to zero.I know i will get 68 bytes from the socket.
QByteArray receivedData = m_tcpSocket->readAll();
 
for(int i=0;i<receivedData.size();++i)
    {
        char result = (receivedData.at(i)^(m_oldData.at(i)));
        qDebug()<<"result "<<result;
        if(result!=0)//means byte is changed
        {
            //To know which bit is changed, this logic is not working. don't know why :(
            for(int j=0;j<8;++j)
            {
               if(result & (1<<j))
               {
                    qDebug()<<"byte index"<<i<<"bit index"<<j <<"is changed";
                    //Now send i and j value to QML.
               }
            }
        }
    }

//How to copy Qbytearray
m_oldData = receivedData//not working.Because of specifying the size of m_oldData. If I don't specify it works. Then How to initialize all the bytes of m_oldData to zero?

Huulivoide

Well first of all QByteArray m_oldData[68] creates an array of QByteArray objects.
If you want a QbyteArray of spesific size you need to use the
QByteArray(int size, char setEveryByteToThisChar) ctor instead.

Also I don't see why you would need to XOR the bytes. A regular == comparison
should do just fine.

QByteArray old_data("initial data bytes");
QByteArray new_data = my_socket->readAll();

for (int i = 0; i < new_data.size(); ++i)
{
    if ((i < old_data.size() && old_data[i] != new_data[i]) || i >= old_data.size())
        emit byteChanged(i, new_value[i]);
}

old_data = new_data;

vishnu

@Huulivoide
Thanks a lot for the reply. I need to access not only each byte. Each bit. I have updated the question again.Sorry for the incomplete question.
I received 68byted of data from the socket looks like this:
01000000000000000000000045020001000000000000000015ef0a0000000000d1f5070015ef0a0000000000d1f507007a77000000000000000000000000000000000000.
Now i have to parse through each byte and then each bit. Then set the bool value of that particular bit to the particular button(true/false).

vishnu

This post is deleted!

Huulivoide

QByteArray old_data(86, '\0') should do it.

if (new_data[i] & (1 << bitPosInByte))
will evaluate true if the bit at offset bitPosInByte in the byte is set.

Huulivoide

No that doesn't work. You need to take the raw char sequence out of the QByteArray
with data() function. Then you can test raw_bytes[i] & (1<<N)

vishnu

@Huulivoide
Sorry I didn't get the point.
QByteArray old_data(68, '\0');
QByteArray receivedData = m_tcpSocket->readAll();
char *receivedDataptr = receivedData.data();// got raw data
for(int i=0;i<receivedData.size();++i)
{
//what is the logic to compare old_data to new_data that gives the bit and byte index which is changed.
for (int bitPosInByte=0; bitPosInByte<8;bitPosInByte++)
{
if (new_data[i] & (1 << bitPosInByte))// This is to get bit position
}
}
//finally i copy
old_data=receivedData ;

Because next time I should come compare with my latest data bytes with old data . Is this what you want to say?

Huulivoide

Sorry I forgot the actual bit comparing.
if ((old_data[i] & (1 << bitPosInByte)) != (new_data[i] & (1 << bitPosInByte)))

That should do it. Does AND on the pesific bit and return true if the AND
results with old and new data are differend.

vishnu

@Huulivoide
works perfect. But how to get the bool value? I mean whether it is true or not.
I tried like this but the value i am getting is in integers.
for eg :byte index 49 bit index 4 is changed value is 16
snippet:

QByteArray receivedData = m_tcpSocket->readAll();
   for(int bytePos=0;bytePos<receivedData.size();++bytePos)
    {
        for(int bitPosInByte=0;bitPosInByte<8;++bitPosInByte)
        {
            if ((m_oldData[bytePos] & (1 << bitPosInByte)) != (receivedData[bytePos] & (1 << bitPosInByte)))
                qDebug()<<"byte index"<<bytePos<<"bit index"<<bitPosInByte <<"is changed"<<"value is "<<bool(receivedData[bytePos] & (1 << bitPosInByte));
        }
  }

SGaist

Working here, what OS/Qt/Compiler combo are you using ?

Huulivoide

@vishnu
It is false if the the bitwise AND is 0, else it it true

vishnu

@SGaist
Windows 7 64bit/ Qt.5.4.1 /MinGw 32bit