Read buffer QSerialPort

erytcg

Hello I have some questions.

I want read buffer from device and send command every 1ms.
Buffer it looks like this: AAAABBBBCCCCDDDDEEEEFFFFGGHHIIJJ
I want read only A,B,C,F. How to get only specific bytes numbers.

Shoud I check currect amount of bytes?
And later save to:

QByteArray data

Access to A,B,C,F only with for loop and QByteArray.append?

After some time I want save this data in Excel file, where keep large amounts of data?

mrjj

Hi
Will it be fixed amount of each ?
like 4 AAAA, 4 BBBB up to f ?

After some time I want save this data in Excel file, where keep large amounts of data?
What do you mean ? And excel sheet is not good for large amounts of data.

erytcg

Yes always 4A , 4B etc.
Maybe .csv file.

mrjj

@erytcg
well then you can just add to the read buffer
when size is 4 x 5, you should have all data.
Then you can process the buffer save save to file or what you need.

erytcg

QByteArray data = serialPort->readAll();
       QByteArray aaaa;
       for (int i = 0; i <= 3 i++)
       {
           aaaa.append(data[i]);
       }

it's ok?

mrjj

@erytcg
Nope, that would crash pretty fast if you receive less than 3 chars first read.

QByteArray data; // move to member of class.

then in read do
data += serialPort->readAll(); // add them up. they might come in blocks.
if (data.size() > 19 ) { // now we got at 20 minimum
... do what u need.
data.clear(); // clear read buffer
}

erytcg

Is there method to read QByteArray some byte?

mrjj

@erytcg
Not that i saw, but you can use
QString AString( data );
then use
http://doc.qt.io/qt-5/qstring.html#mid
to grab only a substring from it

SGaist

Hi,

No need to change classes: QByteArray::mid.

mrjj

@SGaist
Oh, how could it miss that :)