Here goes my Code first.
QByteArray buff;
QDataStream stream(&buff, QIODevice::ReadWrite);
stream.setVersion(QDataStream::Qt_4_7);
stream << 5;
stream << 6;
qDebug() << buff;
int x;
int y;
stream >> x >> y;
qDebug() << x << y;
I expect x be 5 and y be 6. But its showing 0 0
Here is the output
"
0 0
As Frank mentioned the QDataStream is still at the end position (after writing your data). If you don't want to create a new stream, it should also be possible to call stream.reset() to put the stream's internal position to the beginning. Or something like stream.seek(0).
Try this:
QByteArray buff;
QDataStream stream(&buff, QIODevice::ReadWrite);
stream.setVersion(QDataStream::Qt_4_0);
stream << 5;
stream << 6;
qDebug() << buff.toHex();
int x;
int y;
// This line will move the internal QBuffer to position 0
stream.device()->reset();
stream >> x >> y;
qDebug() << x << y;
Output:
"0000000500000006"
5 6
You can't read/write like this from/to a QByteArray using a single QDataStream, at the same time, due to the data stream's internal state (stream position). Try with a second QDataStream for reading.
Related
I have been trying to convert QByteArray data into a hex, bin and char tabular representation, but I encounter problems when in the QByteArray there are escape sequences... for example if I have the QByTeArray which contains "Hello World" the space is not converted into Hex, but it remains a space... what do I do?
for (int i = 0; i < n; i++){
std::cout << "0x" << QString::number(0, 16).toStdString() << "\t";
if (((i+1) % 8) == 0)
std::cout << std::endl;
}
this is the code used for example to run through the QByteArray and transform it into a hex representation.
Btw, I am using QT creator to program in C++ and I'm a beginner
I tried converting the QByteArray into a QString containing the translation into ASCII of the data, so that then maybe with an if else explain the behaviour the program should have every it encounters a number from 00 to 32... but it requires massive effort. Isn't there a shortcut?
In your example, you never use a QByteArray but instead output 0x0 for n iterations.
Assuming, you have some array containing "Hello World", your loop correctly outputs hex values iff you use i to access the array elements and .length() instead of n:
const QByteArray data = "Hello World";
for (int i = 0; i < data.length(); i++){
std::cout << "0x" << QString::number(data[i], 16).toStdString() << "\t";
if (((i+1) % 8) == 0)
std::cout << std::endl;
}
Output:
0x48 0x65 0x6c 0x6c 0x6f 0x20 0x57 0x6f
0x72 0x6c 0x64
The QByteArray class already has QByteArray::toHex() method.
QByteArray arr = "Hello world";
std::cout << QString("0x" + arr.toHex(':')).replace(":", " 0x").toStdString();
I try to send data throw qtcpsocket and use QByteArray. I send previosly size of data and try convert to int like this QByteArray to Int conversion.
But always get 0. Code convertion example:
QString ss = "bca";
int aaa;
QByteArray b;
QDataStream stream(&b, QIODevice::ReadWrite);
stream << ss.toUtf8().size();
stream >> aaa;
In this example aaa is always 0, but ss.toUtf8().size() isnt. What im doing wrong?
QString ss = "bca";
int aaa;
QByteArray b;
QDataStream stream(&b, QIODevice::ReadWrite);
stream << ss.toUtf8().size();
stream.device().seek(0); // add this code
stream >> aaa;
The inner pointer of QByteArray is at the end, so nothing can be read.
I'm not very good at character devices, so I need your help. A have a char device(let's call it /dev/my_light) which is a light sensor. I have to read the data from this file and transform it to the brightness value and then pass it to the brightness manager that changes the brightness of my screen. The problem is that when I read the value for some period of time I get old values from the file.I assume there is a buffer(again not sure how character devices exactly work). Whereas when I use cat /dev/my_light I see new data! Is it possible to get rid off the buffer and read new values that were written to the file just right now. Here is my code in Qt:
void MySensor::updateMySensor()
{
Packet packet;
packet.startByte = 0;
packet.mantissa = 0;
packet.exp = 0;
d->device = ::open(d->path.toStdString().c_str(), O_RDONLY);
if (d->device == -1)
{
qDebug() << Q_FUNC_INFO << "can't open the sensor";
return;
}
ssize_t size = ::read(d->device, &packet, sizeof(packet));
close(d->device);
if (size == -1)
{
qDebug() << errno;
return;
}
packet.exp &= 0x0F;
float illumination = pow(2, packet.exp) * packet.mantissa * 0.045;
if(d->singleShot) emit lightSensorIsRunning(true);
emit illuminationRead(illumination);
}
The mySensor function is called every second. I tried to call it each 200 msec but it didn't help. The value of illumination stays old for about 7 seconds(!) whereas the value that I get from cat is new just immediately.
Thank you in advance!
I can't test with your specific device, however, I'm using the keyboard as a read only device.
The program attempts to connect to keyboard and read all keys pressed inside and outside the window. It's a broad solution you'll have to adapt to meet your demands.
Note that I'm opening the file with O_RDONLY | O_NONBLOCK which means open in read only mode and no wait for the event be triggered(some notifier needed to know when data is ready!) respectively.
You'll need super user privilege to run this example!
#include <QtCore>
#include <fcntl.h>
#include <linux/input.h>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
const char *device_name = "/dev/input/by-path/platform-i8042-serio-0-event-kbd";
int descriptor = open(device_name, O_RDONLY | O_NONBLOCK);
if (descriptor < 0)
{
qDebug() << "Error" << strerror(errno);
return a.exec();
}
QFile device;
if (!device.open(descriptor, QFile::ReadOnly))
{
qDebug() << "Error" << qPrintable(device.errorString());
return a.exec();
}
QSocketNotifier notifier(device.handle(), QSocketNotifier::Read);
QObject::connect(¬ifier, &QSocketNotifier::activated, ¬ifier, [&](int socket){
Q_UNUSED(socket)
struct input_event ev;
QByteArray data = device.readAll();
qDebug() << "Event caught:"
<< "\n\nDATA SIZE" << data.size()
<< "\nSTRUCT COUNT" << data.size() / int(sizeof(input_event))
<< "\nSTRUCT SIZE" << sizeof(input_event);
qDebug() << ""; //New line
while (data.size() >= int(sizeof(input_event)))
{
memcpy(&ev, data.data(), sizeof(input_event));
data.remove(0, int(sizeof(input_event)));
qDebug() << "TYPE" << ev.type << "CODE" << ev.code << "VALUE" << ev.value << "TIME" << ev.time.tv_sec;
}
qDebug() << ""; //New line
});
return a.exec();
}
I'm reimplemented the present method from a QAbstractVideo Surface in order to capture frames from an IP camera.
This is my reimplemented methods (the required ones):
QList<QVideoFrame::PixelFormat> CameraFrameGrabber::supportedPixelFormats(QAbstractVideoBuffer::HandleType handleType) const
{
Q_UNUSED(handleType);
return QList<QVideoFrame::PixelFormat>()
<< QVideoFrame::Format_ARGB32
<< QVideoFrame::Format_ARGB32_Premultiplied
<< QVideoFrame::Format_RGB32
<< QVideoFrame::Format_RGB24
<< QVideoFrame::Format_RGB565
<< QVideoFrame::Format_RGB555
<< QVideoFrame::Format_ARGB8565_Premultiplied
<< QVideoFrame::Format_BGRA32
<< QVideoFrame::Format_BGRA32_Premultiplied
<< QVideoFrame::Format_BGR32
<< QVideoFrame::Format_BGR24
<< QVideoFrame::Format_BGR565
<< QVideoFrame::Format_BGR555
<< QVideoFrame::Format_BGRA5658_Premultiplied
<< QVideoFrame::Format_AYUV444
<< QVideoFrame::Format_AYUV444_Premultiplied
<< QVideoFrame::Format_YUV444
<< QVideoFrame::Format_YUV420P
<< QVideoFrame::Format_YV12
<< QVideoFrame::Format_UYVY
<< QVideoFrame::Format_YUYV
<< QVideoFrame::Format_NV12
<< QVideoFrame::Format_NV21
<< QVideoFrame::Format_IMC1
<< QVideoFrame::Format_IMC2
<< QVideoFrame::Format_IMC3
<< QVideoFrame::Format_IMC4
<< QVideoFrame::Format_Y8
<< QVideoFrame::Format_Y16
<< QVideoFrame::Format_Jpeg
<< QVideoFrame::Format_CameraRaw
<< QVideoFrame::Format_AdobeDng;
}
bool CameraFrameGrabber::present(const QVideoFrame &frame)
{
//qWarning() << "A frame";
if (frame.isValid()) {
//qWarning() << "Valid Frame";
QVideoFrame cloneFrame(frame);
cloneFrame.map(QAbstractVideoBuffer::ReadOnly);
const QImage image(cloneFrame.bits(),
cloneFrame.width(),
cloneFrame.height(),
QVideoFrame::imageFormatFromPixelFormat(cloneFrame .pixelFormat()));
qWarning() << "Is created image NULL?" << image.isNull();
if (!image.isNull())
emit nextFrameAsImage(image);
cloneFrame.unmap();
return true;
}
return false;
}
And this is is how I used it:
grabber = new CameraFrameGrabber(this);
connect(grabber,&CameraFrameGrabber::nextFrameAsImage,this,&QCmaraTest::on_newFrame);
QMediaPlayer *a = new QMediaPlayer(this);
QString url = "http://Admin:1234#10.255.255.67:8008";
a->setMedia(QUrl(url));
a->setVideoOutput(grabber);
a->play();
The problem is that the image that is created is null. As far as I can tell, this can only be because the frame is valid but does not contain data.
Any ideas what the problem could be?
Important Detail: If I set the stream to a QVideoWidget and simply show that, it works just fine.
So I found out what the problem was.
This:
QVideoFrame::imageFormatFromPixelFormat(cloneFrame .pixelFormat())
Was returning invalid format because the IP cam gave the format as a YUV format which QImage can't handle. The solution was to force the format and the only one I found that did not make the program crash was: QImage::Format_Grayscale8.
With that, it worked.
Recently I programmed to do file transmission with Qt. Thought it worked now, I'm still curious about what happened. Please help me find out the reason. Many thanks.
Why the size of head is bigger than the sum of sizeof(qin32), sizeof(qint32) and length of file name?(I guess it is the reason of function - setVersion())
QFileInfo info(file_to_send.fileName());
QByteArray head;
QDataStream out(&head, QIODevice::WriteOnly);
out.setVersion(QDataStream::Qt_5_0);
out << qint32(file_to_send.size() + info.fileName().length() + sizeof(qint32)*2)
<< qint32(info.fileName().length())
<< info.fileName();
tcpClient.write(head);
You have made it to complicated. Pattern is like that:
QFileInfo info(file_to_send.fileName());
QByteArray head;
QDataStream out(&head, QIODevice::WriteOnly);
out.setVersion(QDataStream::Qt_5_0);
out << qint32(0)
<< info.fileName(); // << YouCanAddMoreStuffHere;
out.device()->seek(0);
out << qint32(out.length());
tcpClient.write(head);
and read code:
void SomeClass::slotReadClient() { // slot connected to readyRead signal of QTcpSocket
QTcpSocket *tcpSocket = (QTcpSocket*)sender();
QDataStream clientReadStream(tcpSocket);
while(true) {
if (!next_block_size) {
if (tcpSocket->bytesAvailable() < sizeof(qint32)) { // are size data available
break;
}
clientReadStream >> next_block_size;
}
if (tcpSocket->bytesAvailable() < next_block_size) {
break;
}
QString fileName;
clientReadStream >> fileName; // >> YouCanAddMoreStuffHere; // same as above
next_block_size = 0;
}
}
info.filename() writes out its own length
if you don't want that then you can do
QFileInfo info(file_to_send.fileName());
QByteArray head;
QDataStream out(&head, QIODevice::WriteOnly);
out.setVersion(QDataStream::Qt_5_0);
QByteArray filename = info.fileName().toLatin1();
out << qint32(file_to_send.size() + filename .length() + sizeof(qint32)*2);
<< qint32(filename .length())
out.writeRawData(fileName.constData(), filename.length());
tcpClient.write(head);
using writeRawData which bypasses any built in encoding