Checking QByteArray for certain values

[Spitfire]

What happens if you call client.read(7) twice in a row?
Do you get the same output twice?

Instead of returning the output straight away create temporary variable and return that variable and see what happens.
IMHO it should make no difference.

[-Kyr0s-]

I've tried what you suggested, but to no avail.

QByteArray bytes;
 
    bytes.push_back(1);
    bytes.push_back(2);
    bytes.push_back(NULLPTR);
    bytes.push_back(1);
    bytes.push_back(dio_n);
 
    client.write(bytes);
    buffer = client.read(7);
    this->ui->txtbxOutput->append(buffer.toHex());
 
    return buffer;

QByteArray bytes;

    bytes.push_back(1);
    bytes.push_back(2);
    bytes.push_back(NULLPTR);
    bytes.push_back(1);
    bytes.push_back(dio_n);

    client.write(bytes);
    buffer = client.read(7);
    this->ui->txtbxOutput->append(buffer.toHex());

    return buffer;

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Buffer is a QByteArray.

Also, maybe worth noting, is that the textbox won't show any output, until I click one of the checboxes. Oddly enough, when the application starts, it does go through read_bytes() and thus, is supposed to print out the string. It doesn't do that, only after having clicked a checkbox it would, whilst it goes through the same function as start-up.

I don't know why it doesn't immediately parse the output in the textbox, as it's pretty much the very same functions..

[-Kyr0s-]

Hello,

I've decided to redo the application to see where it goes wrong. It seems everything works fine; it writes and reads the appropriate number of bytes. Reading is supposed to send 5 bytes, and receive 7 in return.

However, once it accesses the isOn() method, these bytes turn into 20.

I suspect it's due to this:

this->ui->chkDIO0->setChecked(this->isOn(0));
    this->ui->chkDIO1->setChecked(this->isOn(1));
    this->ui->chkDIO2->setChecked(this->isOn(2));
    this->ui->chkDIO3->setChecked(this->isOn(3));

this->ui->chkDIO0->setChecked(this->isOn(0));
    this->ui->chkDIO1->setChecked(this->isOn(1));
    this->ui->chkDIO2->setChecked(this->isOn(2));
    this->ui->chkDIO3->setChecked(this->isOn(3));

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Each time it goes through reading bytes, it sends 5 bytes, so 5x4 is 20. I guess that makes sense, but even if it didn't, readBytes in isOn() remains to be an empty string.

QByteArray DIOMoxaBoard::read_bytes(quint16 dio_n)
{
    /* *******************************
       * 1st byte: Command number, 1
       * 2nd byte: Version, 2
       * 3rd byte: Response only, any
       * 4th byte: Data length, 1
       * 5th byte: DIO channel
       ********************************/
 
    QByteArray bytes;
 
    bytes.push_back(1);
    bytes.push_back(2);
    bytes.push_back(_NULL);
    bytes.push_back(1);
    bytes.push_back(dio_n);
 
    client.write(bytes); // successfully writes 5 bytes if it doesn't access isOn()
 
    return client.read(7).toHex(); //successfully reads 7 bytes if it doesn't access isOn()
}
 
bool DIOMoxaBoard::isOn(quint16 dio_n)
{
    bool isOn = false;
    const char ON = 0x00;
    const int switchIndex = 6;
 
    QByteArray readBytes = this->read_bytes(dio_n); //readBytes remains ""
 
    if(readBytes.size() > switchIndex && readBytes[switchIndex] == ON)
        isOn = true;
    else
        isOn = false;
 
    return isOn;
}

QByteArray DIOMoxaBoard::read_bytes(quint16 dio_n)
{
    /* *******************************
       * 1st byte: Command number, 1
       * 2nd byte: Version, 2
       * 3rd byte: Response only, any
       * 4th byte: Data length, 1
       * 5th byte: DIO channel
       ********************************/

    QByteArray bytes;

    bytes.push_back(1);
    bytes.push_back(2);
    bytes.push_back(_NULL);
    bytes.push_back(1);
    bytes.push_back(dio_n);

    client.write(bytes); // successfully writes 5 bytes if it doesn't access isOn()

    return client.read(7).toHex(); //successfully reads 7 bytes if it doesn't access isOn()
}

bool DIOMoxaBoard::isOn(quint16 dio_n)
{
    bool isOn = false;
    const char ON = 0x00;
    const int switchIndex = 6;

    QByteArray readBytes = this->read_bytes(dio_n); //readBytes remains ""

    if(readBytes.size() > switchIndex && readBytes[switchIndex] == ON)
        isOn = true;
    else
        isOn = false;

    return isOn;
}

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Any idea how to avoid sending 20 bytes due to calling isOn() four times for each checkbox (I've tried pause/sleep already), as well as being able to pass on the buffer values to the new variable readBytes, instead of having it remain as an empty string?


Thanks in advance!

[gouyoku]

Hi

I am no expert but here are some of my thoughts:
You shouldn't use client.read() right after client.write(). Getting data over the network is asynchronous so you need to give it time to arrive.
If I were to guess, you are using QAbstractSocket as your client. If so, you should use its signal readyRead() to know when to read the answer.
This would explain why your program prints out your string only after you click a checkbox. At first pass of read_bytes() you don't have anything to read() as the answer have not arrived yet.
To set your checkboxes you will need to implement some queue, for example: isOn(0); readyRead()->setchecked()->isOn(1); readyRead()->setChecked()->isOn(2); and so on.

Hope it helps.

[Lesiok]

In line 21 You are converting binary data to hex (that is to say hexadecimal character notation). So method read_bytes() returns more when 2 x 7 bytes. Next in line 32 You compare this character to binary value ON. This have no sense.