通过TCP将图像从labVIEW发送到QT

Question

I am trying to capture images taken from a camera connected to a myRIO and send them over a TCP/IP connection from labVIEW to a QT GUI application.

My problem is that QT keeps throwing a heap pointer exception and crashing when I read the data. Expression: is_block_type_valid(header->_block_use)

I believe this could be because the data being sent is over 35k bytes, so I tried to read the data in separate chunks, but alas am still getting the error.

Below is my function that gets called on readyRead() being emitted:

void TCPHandler::onRead() {


QByteArray byteArray;
QByteArray buffer;
QByteArray dataSize = mainSocket->read(5); //read the expected amount of bytes incoming (about 35000)
while (buffer.size() < dataSize.toInt()) {
    int bytesLeft = dataSize.toInt() - buffer.size();
    if (bytesLeft < 1024) {
        byteArray = mainSocket->read(bytesLeft);
    }
    else {
        byteArray = mainSocket->read(1024);
    }

    buffer.append(byteArray);
}
QBuffer imageBuffer(&buffer);
imageBuffer.open(QIODevice::ReadOnly);

QImageReader reader(&imageBuffer, "JPEG");
QImage image;
if(reader.canRead())
    image = reader.read();
else {
    emit read("Cannot read image data");
}

if (!image.isNull())
{
    image.save("C:/temp");
}
else
{
    emit read(reader.errorString());
}}

In the LabVIEW code I send the size of the bytes being sent first, then the raw image data:

EDIT: Connect for the slot. Also should have mentioned this is running in a separate thread to the Main GUI.

TCPHandler::TCPHandler(QObject *parent)
    : QObject(parent),
    bytesExpected(0)
{
    mainSocket = new QTcpSocket(this);

    connect(mainSocket, SIGNAL(readyRead()), this, SLOT(onRead()));
    connect(mainSocket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error), this, &TCPHandler::displayError);
}

Answer 1

You are sending your length as a decimal string. Then followed by the string. I would expect that the length would be binary value. So instead of an 'I32 to String' function use a typecast with a string as the type.