serial port in dll

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

chr_sch

@SGaist
I red this chapter already and my header files as well as the pro file are as specified in the explanation:
dll.h:

#ifndef MESSWERT_ZUORDNUNG_DLL_H
#define MESSWERT_ZUORDNUNG_DLL_H

#include "messwert_zuordnung_dll_global.h"

MESSWERT_ZUORDNUNG_DLLSHARED_EXPORT void Test(int a);

class MESSWERT_ZUORDNUNG_DLLSHARED_EXPORT Messwert_zuordnung_dll
{

public:
    Messwert_zuordnung_dll();

    void Test(int a);
};

#endif // MESSWERT_ZUORDNUNG_DLL_H

dll_global.h

#ifndef MESSWERT_ZUORDNUNG_DLL_GLOBAL_H
#define MESSWERT_ZUORDNUNG_DLL_GLOBAL_H

#include <QtCore/qglobal.h>

#if defined(MESSWERT_ZUORDNUNG_DLL_LIBRARY)
#  define MESSWERT_ZUORDNUNG_DLLSHARED_EXPORT Q_DECL_EXPORT
#else
#  define MESSWERT_ZUORDNUNG_DLLSHARED_EXPORT Q_DECL_IMPORT
#endif

#endif // MESSWERT_ZUORDNUNG_DLL_GLOBAL_H

I cant see a big difference.

SGaist

Following your various piece of code, you don't have any class called MyLib containing Test(int) nor any namespace containing such a function

chr_sch

@SGaist
I changed the name, because the actual is a bit long. My class is Messwert_zuordnung_dll.
The function for the export is Test.

SGaist

Ok so your

MyLib c;
c.test(b);

should rather be:

Messwert_zuordnung_dll mzd;
mzd.Test(b);

correct ?

So, when you are building your dll, do you get both the dll and corresponding lib file ?

chr_sch

@SGaist
Yes that´s correct. Sorry at this point for the confusion with the names.

Yes the build creates a .dll/.lib and .obj file.
At the beginning I had some trouble with the link I set as dependent path and libs in the pro file because there where a space in it. The error said "could not open .obj" so maybe it the program tries to open the .obj instead of the .dll ?

SGaist

No, you should link to the lib file. However having space in your path on Windows is generally a Bad Thing (™) so just avoid them altogether

chr_sch

@SGaist
Yes I realized that this is a problem and renamed the folder. But this was just at the beginning, now it has to be an other problem

SGaist

It still can't find it ? Did you implement Test(int a) ?

chr_sch

@SGaist
What exactly do you mean with implement ?
Under the exportet class in "public" I added "void Test(int a)" and right clicked refractor and added the function to the cpp file.