serial port in dll

SGaist

Did you check that you are doing the property symbol exporting ? Define name for activating the export macro etc. ?

t3685

Do you this macro: MESSWERT_ZUORDNUNG_DLL_LIBRARY defined in the pro file of your library?

chr_sch

I choose to use QLibrary instead of implementing the dll by myself. Therefore I used the following code in my main.cpp:

 QLibrary library("Messwert_Zuordnung_DLL.dll");
    if (!library.load())
    qDebug() << library.errorString();
    if (library.load())
    qDebug() << "library loaded";

    library.resolve("uebergabe");

I am not really shure, that this is the proper use of QLibrary but it builds without an error.
So I think it might work.
If my dll gives simply the value in qDebug() out which I write in the dll function in my test programm it works.
But if I try to establish a serial connection, my microcontroller does not recognize a input. So there is a fault in the use of the QSerialPort in my code. The same code is used in a GUI where it works. I only did not use the connect() function and in the definition of my port serial* = new QSerialPort (this) I didn´t write this. Because I have no parent object here. Do I have to establish a QObject for this ? Or is there any other problem with the use of QSerialPort in a dll ?

Here is my code:

QSerialPort *serial;
 serial = new QSerialPort();


    //+++++++++++++++++++++++++++++++++++
    //+++++++++++++++++++++++++++++++++++
    //COM-Port !

    serial->setPortName("COM12");

    //+++++++++++++++++++++++++++++++++++
    //+++++++++++++++++++++++++++++++++++


    serial->setBaudRate(QSerialPort::Baud115200);
    serial->setDataBits(QSerialPort::Data8);
    serial->setParity(QSerialPort::NoParity);
    serial->setStopBits(QSerialPort::OneStop);
    serial->setFlowControl(QSerialPort::SoftwareControl);


    serial->open(QIODevice::ReadWrite);


            //conversion of the variables for the use of the send function


            QByteArray messint_s = QByteArray::number(messint);
            QByteArray bauteillaenge_s = QByteArray::number(bauteillaenge);
            QByteArray interpol_s = QByteArray::number(interpol);
            QByteArray anz_messungen_s = QByteArray::number(anz_messungen);
            QByteArray abs_messungen_s = QByteArray::number(abs_messungen);

            //Sending the variables to my microcontroller
            serial->write("1");
            serial->write("\n");

regards

SGaist

Was it dll_tester that you failed to link ? If so, you were not linking to the library.

You need to delete serial by hand when not using it anymore otherwise you'll be leaking memory

chr_sch

@SGaist
I don´t know where my fault was. I think it was some linking problem but I don´t know how to solve so I use QLibrary.

Ok you mean that I have to close the serialport at the end of the dll ?
Can you see any other fault? Because the serial connection is not working .

SGaist

You have to delete serial. IIRC that should also close it.

In any case, you should recheck your project and make it link properly to your library. Using QLibrary as a workaround is not the proper thing to do.

chr_sch

@SGaist
Yes but this should only be a test program to see if the dll works correctly. In the end the dll is used in an othe context, so I want to focus on the function of the dll. Alltough it would be nice to know where my fault was. But I did everything like in the description in the links above nothing works, so I have to move on to loos not more time.

But why doesn´t works my serial connection ? That is in the moment my biggest problem.
Do I have to create a QObject as parent when I don´t have a window as parent ?
Is the connect function necessary ?
I thought the use is only to refer the connection fe to a button. But in a dll it should be unnecessary.

Is this maybe the troublemaker?

SGaist

Why it doesn't work ? I can't tell, that's Crystal Ball debugging at this point. However, you don't check that that your device opened successfully

chr_sch

@SGaist

Yeah that´s kind of diffucult. But I need help because I dont´t know how to figure out where my problem is.
I tried in a working serial port GUI to delete the connect() function and the "this" in new QSerialPort(this). It is still working. So the code should work.

With : if(!serial->open(QIODevice::ReadWrite)){qDebug()<<"Connection failed"}. I figured out, that the connection is not opened.

I get the return value: -1073741510. Knows anybody what this means?

regards

SGaist

Your application has been aborted e.g. you stopped it brutally.

Did you check the returned error ? What is it ?

chr_sch

@SGaist
How to check the error ? My program runs without showing an error. But there has to be one because the serial connection can´t be opened.

I tried to use : qDebug()<< serial->errorString();
But the output was "Unkown error".

SGaist

Ok, then just create on minimal application that opens that serial port and tries to write to / read from it. That will at least help check that your serial port is working correctly

chr_sch

@SGaist
My first project was a GUI that communicates with that serial port.
This still works fine. I used the same code to implement the serial connection in the dll file. Only the parent object, if i create the new QSerialPort, in thr parenthesis is empty. And i do not use the connect () function. If i change the code in the GUI it still works.
In the GUI as well as in the dll the serial connection us only used to send a few variables to a microcontroller. So it should be a minimal requirement to the serial. Maybeit it is not possible to write a dll that opens a serial port at runtime ?

SGaist

There's no such restriction.

Since you had trouble with the library in the first place, the next step is to create a minimal library that will provide some dummy function and link to it. Don't use QLibrary to load, just make your application link to it properly.

chr_sch

@SGaist

Ok I just tried to create a new one.
My steps:
*Qt Creator -> new -> dll
*add a dummy function under public in my header
*dummy function in the cpp file: qDebug() << dll works

*create a new console application
*right click add existing file: mark the two header files from my dll
*set the paths: -> INCLUDEPATH += folder from my dll where the headers are
->DEPENDPATH+= same folder as above
->LIBS+= -Ldebug folder of my dll file -lname of my dll file
*copy the dll in the debug folder of the test program
*in the test programm i add in the cpp file:
-> include the header
->create new object
-> call the function from the dll

All works well. But if I try to pass an integer through the function to my dll I get an unresolved symbol error.
After I changed my dll I re-build it and changed the copied files through the new ones.

SGaist

Can you show the code where you pass that integer ?

chr_sch

@SGaist

In the dll i specified the following function:
-header
public:
void Test(int a);

-cpp
qDebug()<< a;

in the Test program:
int b=1;
MyLib c ;
c.test(b);

The exact error message is:
main.obj:-1: Error: LNK2019: unresolved symbol ""__declspec(dllimport) public: void __cdecl MyLib::Test(int)" (_imp?Test@MyLib@@QEAAXH@Z)" in function "main".

SGaist

You are not exporting Test properly

chr_sch

@SGaist
How to do so ?
Where is my fault ?

SGaist

You have a nice explanation in the Creating shared libraries chapter of Qt's documentation