QSerialPort not working, but shows no errors (Ubuntu)

[Brixus]

Hello,

I need to use QSerialPort together with a USB serial adapter on Ubuntu.
This is a FT232RL which is mounted as "ttyUSB0".

Using CuteCom I can use the serial adapter and it is working fine.

Sadly with QT I am not able to access ttyUSB0.

I get no errors while compiling and executing the programm leads to an empty console window which freezes :-(

If I change ttyUSB0 to some not existing thing like ttyUSB, I get the error that he could not open the device.
So this is actually good.

But I have no Idea, how to solve my problem :-(

It would be really nice if you could help me.

Thank you very much :-)


This is the code I tried:

#include <iostream>
 
#include <QApplication>
#include <QSerialPort>
 
using namespace std;
 
QSerialPort serial;
 
 
int main (int argc, char *argv[])
{
   QApplication app(argc, argv);
   serial.setPortName("/dev/ttyUSB0");  
   serial.open(QIODevice::WriteOnly); 
   serial.setBaudRate(QSerialPort::Baud19200);
   serial.setDataBits(QSerialPort::Data8);
   serial.setParity(QSerialPort::NoParity);
   serial.setStopBits(QSerialPort::OneStop);
   serial.setFlowControl(QSerialPort::NoFlowControl);
 
 
 
    for (int i=0; i<100; i++)
    {
        serial.write("test");
        serial.flush();
        cout << i << endl;
    }
 
    serial.close();
    return 0;
}

#include <iostream>

#include <QApplication>
#include <QSerialPort>

using namespace std;

QSerialPort serial;


int main (int argc, char *argv[])
{
   QApplication app(argc, argv);
   serial.setPortName("/dev/ttyUSB0");  
   serial.open(QIODevice::WriteOnly); 
   serial.setBaudRate(QSerialPort::Baud19200);
   serial.setDataBits(QSerialPort::Data8);
   serial.setParity(QSerialPort::NoParity);
   serial.setStopBits(QSerialPort::OneStop);
   serial.setFlowControl(QSerialPort::NoFlowControl);



    for (int i=0; i<100; i++)
    {
        serial.write("test");
        serial.flush();
        cout << i << endl;
    }

    serial.close();
    return 0;
}

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And this is my .pro file:

QT       += core serialport widgets
 
QT       -= gui
 
TARGET = Timer
CONFIG   += console
CONFIG   -= app_bundle
 
TEMPLATE = app
 
 
SOURCES += main.cpp 
QMAKE_CXXFLAGS += -std=c++0x

QT       += core serialport widgets

QT       -= gui

TARGET = Timer
CONFIG   += console
CONFIG   -= app_bundle

TEMPLATE = app


SOURCES += main.cpp 
QMAKE_CXXFLAGS += -std=c++0x

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[wysota]

Shouldn't you be setting the options before opening the port? And I would suggest to avoid making the port object a global variable.

[Lesiok]

As I recall QSerialPort needs an event loop or the use of method waitForBytesWritten();

[ChrisW67]

Also check that the user you are running as has read and write permission to that port. Usually this means a particular group membership. ( Cutecom may be working only because it is marked setuid or setgid.)

[Brixus]

Sorry for the late reaction.

I had no Internet on the last days :-(


I found out the problem.

The last hint with the permissions was quiet good. :-)

There was a lockfile on the port.
After deleting the lockfile in the folder /var/lock everything worked well :-)

Thank you very much!