#include <QSerialPort>
#include <QSerialPortInfo>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
// Example use QSerialPortInfo
foreach(const QSerialPortInfo &info, QSerialPortInfo::availablePorts()) {
// Example use QSerialPort
QSerialPort serial;
serial.setPort(info);
if (serial.open(QIODevice::ReadWrite))
//I try to send a string of hexadecimal numbers，seems not right
//serial.write(QByteArray("0xFF010100FFFFFF"));
serial.close();
}
return a.exec();
}
The example above shows how to open all available serial ports and then close them. But I want to open a given serial port, such as COM6, set its BaudRate,DataBits,Parity,StopBits ,FlowControl and then send a string of hexadecimal numbers.
This video will definitely help you: https://www.youtube.com/watch?v=UD78xyKbrfk
You can also find similar code here: https://cboard.cprogramming.com/cplusplus-programming/169624-read-write-serial-port.html
Example code:
#include <QSerialPort>
MySerialPort::MySerialPort()
{
serial = new QSerialPort(this);
openSerialPort();
}
void MySerialPort::openSerialPort()
{
serial->setPortName("COM3");
serial->setBaudRate(QSerialPort::Baud9600);
serial->setDataBits(QSerialPort::Data8);
serial->setParity(QSerialPort::NoParity);
serial->setStopBits(QSerialPort::OneStop);
serial->setFlowControl(QSerialPort::NoFlowControl);
if (serial->open(QIODevice::ReadWrite))
{
//Connected
}
else
{
//Open error
}
}
void MySerialPort::writeData(const QByteArray &data)
{
serial->write(data);
}
Related
I need to loopback audio recorded from the microphone straight to the speaker using QT (qt 5.7 on Windows...) - assume I can't use window's internal mic->speaker loopback (enable "listen to this device" on the microphone panel).
Any direction how to do that?
Based on the discussion on https://forum.qt.io/topic/19960/qaudioinput-redirect-to-qaudiooutput/3
#include <iostream>
#include <QCoreApplication>
#include <QAudioInput>
#include <QAudioOutput>
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
const auto decideAudioFormat = [](const QAudioDeviceInfo& devInfo)
{
QAudioFormat format;
format.setSampleRate(8000);
format.setChannelCount(1);
format.setSampleSize(16);
format.setCodec("audio/pcm");
format.setByteOrder(QAudioFormat::LittleEndian);
format.setSampleType(QAudioFormat::SignedInt);
if (devInfo.isFormatSupported(format))
{
return format;
}
else
{
std::cerr << "Raw audio format not supported by backend, cannot play audio.\n";
throw 0;
}
};
QAudioInput audioInput(decideAudioFormat(QAudioDeviceInfo::defaultInputDevice()));
QAudioOutput audioOutput(decideAudioFormat(QAudioDeviceInfo::defaultOutputDevice()));
audioOutput.start(audioInput.start());
return app.exec();
}
Adding a buffer in-between
I've encountered this issue before. If I'm not mistaken, the read() and write() functions share the same pos() tracker. This is what happens:
QBuffer buffer;
buffer.open(QBuffer::ReadWrite); // buffer.pos() == 0
buffer.write(someData, 5); // Writes in positions 0 -- 4, buffer.pos() == 5;
buffer.write(someData, 5); // Writes in positions 5 -- 9, buffer.pos() == 10;
buffer.read(otherBuffer.data(), 10); // Tries to read from position 10 onwards. No data found
2 solutions:
Implement your own, separate read-position and write-position trackers. Then, call seek() in readData() and writeData() to set pos() -- point to the end of the data before writing, but point to the middle of the data before reading
Use 2 separate buffers, and copy bytes from the input buffer into the output buffer
So, with separate buffers:
#include <iostream>
#include <cassert>
#include <QCoreApplication>
#include <QAudioInput>
#include <QAudioOutput>
#include <QBuffer>
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
QBuffer rdBuff;
QBuffer wrBuff;
wrBuff.open(QBuffer::WriteOnly);
rdBuff.open(QBuffer::ReadOnly);
QObject::connect(&wrBuff, &QIODevice::bytesWritten, [&wrBuff, &rdBuff](qint64)
{
// remove all data that was already read
rdBuff.buffer().remove(0, rdBuff.pos());
// set pointer to the beginning of the unread data
const auto res = rdBuff.seek(0);
assert(res);
// write new data
rdBuff.buffer().append(wrBuff.buffer());
// remove all data that was already written
wrBuff.buffer().clear();
wrBuff.seek(0);
});
const auto decideAudioFormat = [](const QAudioDeviceInfo& devInfo)
{
QAudioFormat format;
format.setSampleRate(8000);
format.setChannelCount(1);
format.setSampleSize(16);
format.setCodec("audio/pcm");
format.setByteOrder(QAudioFormat::LittleEndian);
format.setSampleType(QAudioFormat::SignedInt);
if (devInfo.isFormatSupported(format))
{
return format;
}
else
{
std::cerr << "Raw audio format not supported by backend, cannot play audio.\n";
throw 0;
}
};
QAudioInput audioInput(decideAudioFormat(QAudioDeviceInfo::defaultInputDevice()));
QAudioOutput audioOutput(decideAudioFormat(QAudioDeviceInfo::defaultOutputDevice()));
audioInput.start(&wrBuff);
audioOutput.start(&rdBuff);
return app.exec();
}
This question already has answers here:
When should Q_OBJECT be used?
(4 answers)
QT "No such slot" Error [duplicate]
(1 answer)
Closed 6 years ago.
I have written an UDP programme with Qt, and when I connect this:
connect(socket,SIGNAL(readyRead()),this,SLOT(processPendingDatagrams()));
the complier tells me that
no such slot
the error click here
and I want to know how to fix it, thank you!
P.S.
Here are my files:
files
Here are my codes:
enter code here
udptest.cpp:
#include "udptest.h"
#include <QObject>
#include <QUdpSocket>
#include <QtNetwork>
UDPtest::UDPtest()
{
socket = new QUdpSocket();
port = 2016;
socket->bind(port,QUdpSocket::ShareAddress
| QUdpSocket::ReuseAddressHint);
connect(socket,SIGNAL(readyRead()),this,SLOT(processPendingDatagrams()));
}
QString UDPtest::getIP()
{
QList<QHostAddress> list = QNetworkInterface::allAddresses();
foreach (QHostAddress address, list)
{
if(address.protocol() == QAbstractSocket::IPv4Protocol)
return address.toString();
}
return 0;
}
void UDPtest::sendMessage(QString message)
{
QByteArray data;
QDataStream out(&data,QIODevice::WriteOnly);
QString localHostName = QHostInfo::localHostName();
QString address = getIP();
out <<"123"<< localHostName << address << message;
socket->writeDatagram(data,data.length(),QHostAddress::Broadcast, port);
}
void UDPtest::processPendingDatagrams()
{qDebug()<<"receive";
while(socket->hasPendingDatagrams())
{
QByteArray datagram;
datagram.resize(socket->pendingDatagramSize());
socket->readDatagram(datagram.data(),datagram.size());
QDataStream in(&datagram,QIODevice::ReadOnly);
QString userName,localHostName,ipAddress,message;
QString time = QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss");
in >>userName >>localHostName >>ipAddress >>message;
QString msg=time+userName+localHostName+ipAddress+message;
msger=msg;
qDebug()<<msg;
}
}
QString UDPtest:: messager()
{
return msger;
}
main.cpp:
#include"udptest.h"
#include<QDebug>
#include <QtCore/QCoreApplication>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
qDebug()<<"123";
UDPtest test;
test.sendMessage("aha");
return a.exec();
}
udptest.h:
#ifndef UDPTEST_H
#define UDPTEST_H
#include <QObject>
#include <QUdpSocket>
#include <QtCore/QCoreApplication>
#include <QtNetwork>
class UDPtest:public QObject
{
public:
UDPtest();
QString messager();
void sendMessage(QString);
private slots:
void processPendingDatagrams();
private:
QString msger;
QUdpSocket *socket;
qint16 port;
QString getIP();
};
#endif // UDPTEST_H
QudptestConsole.pro:
QT += core
QT -= gui
QT += network
CONFIG += c++11
TARGET = QudptestConsole
CONFIG += console
CONFIG -= app_bundle
TEMPLATE = app
SOURCES += main.cpp \
udptest.cpp
HEADERS += \
udptest.h
You have forgotten Q_OBJECT macro in UDPtest class
class UDPtest: public QObject
{
Q_OBJECT
public:
UDPtest();
.....
}
I try to send a message via dbus-send to this small example program.
But it is not received:
dbus-send --session --type=method_call / dbustester.test.slot_foo
The return code is 0 and not message is printed to the console.
Below is the source code.
main.cpp
#include <QtCore/QCoreApplication>
#include <QtCore/QDebug>
#include <QtDBus/QtDBus>
#include <Example.h>
int main(int argc, char **argv)
{
QCoreApplication app(argc, argv);
Example *e = new Example();
e->setupDBus();
return app.exec();
}
Example.h
#include <QtCore/QCoreApplication>
#include <QtCore/QDebug>
#include <QtDBus/QtDBus>
class Example : public QObject
{
Q_OBJECT
Q_CLASSINFO("D-Bus Interface", "dbustester.test")
public:
Example(QObject* parent = NULL) :
QObject(parent)
{
}
void setupDBus()
{
QDBusConnection session = QDBusConnection::sessionBus();
if (!session.isConnected())
{
qFatal("Cannot connect to the D-Bus session bus.");
return;
}
session.connect("", "/", "dbustester.test", "slot_foo", this, SLOT(slot_foo(void)));
if(!session.registerObject("/", this, QDBusConnection::ExportScriptableContents)) {
qFatal("Cannot registerObject.");
return;
}
if(!session.registerService("dbustester.test")) {
qFatal("Cannot registerObject.");
return;
}
}
public slots:
Q_SCRIPTABLE void slot_foo()
{
qDebug() << "request received";
}
};
Build:
qmake -project
echo "CONFIG += qdbus" >> *.pro
qmake
I've found the answer while writing the question, but I wrote the question anyway. Some people might find it useful.
dbus-send --session --dest=dbustester.test --type=method_call / dbustester.test.slot_foo
I forgot the --dest argument. :>
I want to start a process from a QT app and catch its termination event. Its done with the method QProcess::start(). But unlike in startDetached(), the standard output of the process is redirected to a buffer. I don't want that.
I can't find how to disable it. An ugly workaround is to call setStandardOutputFile("/dev/stdout")
test.h
#ifndef MY_TEST_H
#define MY_TEST_H
#include <QCoreApplication>
class MyApp : public QCoreApplication {
Q_OBJECT
private Q_SLOTS:
void subprocessStarted();
void subprocessFinished(int);
public:
MyApp( int & argc, char ** argv );
};
#endif
test.cpp
#include "test.h"
#include <QProcess>
#include <QCoreApplication>
#include <stdio.h>
#define ENTRY printf("%s\n", __PRETTY_FUNCTION__)
MyApp::MyApp( int & argc, char ** argv ) : QCoreApplication(argc, argv) {
ENTRY;
QProcess *process = new QProcess();
//process->setStandardOutputFile("/dev/stdout");
process->start("/bin/echo aaa");
bool b;
b = connect(process, SIGNAL(started()), SLOT(subprocessStarted()));
printf("connect started %d\n", b);
b = connect(process, SIGNAL(finished(int)), SLOT(subprocessFinished(int)));
printf("connect finished %d\n", b);
}
void MyApp::subprocessStarted() {
ENTRY;
}
void MyApp::subprocessFinished(int ret) {
ENTRY;
printf("%d\n", ret);
}
int main(int argc, char *argv[]) {
ENTRY;
MyApp a(argc, argv);
return a.exec();
}
Does QProcess::closeReadChannel(ProcessChannel channel) work for you?
Closes the read channel channel. After calling this function, QProcess
will no longer receive data on the channel. Any data that has already
been received is still available for reading. Call this function to
save memory, if you are not interested in the output of the process.
Like this-
QProcess *process = new QProcess();
process->start("/bin/echo aaa");
process->closeReadChannel(QProcess::StandardOutput);
process->closeReadChannel(QProcess::StandardError);
I am trying to display and get the result a message box from outside of a QObject class. I seem to be able to generate the dialog like this:
#include <iostream>
#include <QApplication>
#include <QtConcurrentRun>
#include <QMessageBox>
class DialogHandler : public QObject
{
Q_OBJECT
signals:
void MySignal();
public:
DialogHandler()
{
connect( this, SIGNAL( MySignal() ), this, SLOT(MySlot()) );
}
void EmitSignal()
{
emit MySignal();
}
public slots:
void MySlot()
{
QMessageBox* dialog = new QMessageBox;
dialog->setText("Test Text");
dialog->exec();
int result = dialog->result();
if(result)
{
std::cout << "ok" << std::endl;
}
else
{
std::cout << "invalid" << std::endl;
}
}
};
#include "main.moc" // For CMake's automoc
void MyFunction(DialogHandler* dialogHandler)
{
dialogHandler->EmitSignal();
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
DialogHandler* dialogHandler = new DialogHandler;
MyFunction(dialogHandler);
return app.exec();
}
To get the result back in MyFunction, it seems to work to do simply pass an object to fill with the result like this:
#include <iostream>
#include <QApplication>
#include <QtConcurrentRun>
#include <QMessageBox>
class DialogHandler : public QObject
{
Q_OBJECT
signals:
void MySignal(int* returnValue);
public:
DialogHandler()
{
connect( this, SIGNAL( MySignal(int*) ), this, SLOT(MySlot(int*)), Qt::BlockingQueuedConnection );
}
void EmitSignal(int* returnValue)
{
emit MySignal(returnValue);
}
public slots:
void MySlot(int* returnValue)
{
std::cout << "input: " << *returnValue << std::endl;
QMessageBox* dialog = new QMessageBox;
dialog->addButton(QMessageBox::Yes);
dialog->addButton(QMessageBox::No);
dialog->setText("Test Text");
dialog->exec();
int result = dialog->result();
if(result == QMessageBox::Yes)
{
*returnValue = 1;
}
else
{
*returnValue = 0;
}
}
};
#include "main.moc" // For CMake's automoc
void MyFunction(DialogHandler* dialogHandler)
{
int returnValue = -1;
dialogHandler->EmitSignal(&returnValue);
std::cout << "returnValue: " << returnValue << std::endl;
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
DialogHandler* dialogHandler = new DialogHandler;
QtConcurrent::run(MyFunction, dialogHandler);
std::cout << "End" << std::endl;
return app.exec();
}
Does that seem reasonable? Is there a better way to do it?
This isn't possible quite like you have it, but with a bit of work it could be done. One option, of course, would be to convert your class to a QObject, at which point you could send signals. It doesn't help for the delay during exec, however. If that is necessary, you could have a messaging class that lives in the main UI thread, but can be called from other threads. The function called from other threads would need to lock, make a semaphore, and send an event to itself with the semaphore and message to be displayed. Then, in customEvent (which would be in the UI thread), you would create the message box, exec it, and trigger the semaphore after the message box is cleared.
Of course, things get a bit more complicated if you need to send information back the other way as well. Then you'll need a complete subsystem for your program, instead of just one basic class like I describe here.