Export C++ class from Qt Library on Windows

  • I have created a Qt shared library project using Qt Creator 2.1 (vc 2008 compiler) and Qt Library 4.7.3 on Windows.

    in QtSharedLib_global.h:

    @#if defined(QTSHAREDLIB_LIBRARY)





    in QtSharedLib.h:

    @#include "QtSharedLib_global.h"

    int Sub(int a, int b);

    in QtSharedLib.h:

    @include "QtSharedLib.h"

    int QtSharedLib::Sub(int a, int b)
    return (a-b);

    I can build it successfully.

    In my widget application. in MainWindow.cpp funtion - on_pushButton_clicked():

    @ QtSharedLib *lib = new QtSharedLib();
    int c = lib->Sub(4, 3);@

    in the .pro:
    @QT += core gui
    TARGET = Qt_WidgetApp
    TEMPLATE = app
    SOURCES += main.cpp MainWindow.cpp
    HEADERS += MainWindow.h
    FORMS += MainWindow.ui
    INCLUDEPATH += ../QtSharedLib

    LIBS += C:/Qt_Test/QtSharedLib-build-desktop/debug/QtSharedLib.lib@

    I can build it successfully. But when I run it, I got popup dialog say exception triggered: The inferior stopped because it triggered an exception. Stopped in thread 0...

    What is the problem?

    I can import / export functions. But do not know how to inport / export class.

  • OK. I figure out something.

    I forget to mention something. In the library project, I also have: FunctionsLib.h/cpp

    in FunctionsLib.h
    @#include "QtSharedLib_global.h"
    QTSHAREDLIBSHARED_EXPORT int Add(int a, int b);@

    in FunctionsLib.cpp
    @#include "FunctionsLib.h"
    QTSHAREDLIBSHARED_EXPORT int Add(int a, int b)
    return (a+b);

    If I remove the FunctionsLib.h/cpp from library. Then build both dll and widget application project OK and Run application no error.

    So question is:

    Can I include multiple h/cpp files in the library? If yes, how to do it? if no, then how to export multiple classes? I like one file for one class.

  • Moderators

    Yes, you can have severeal .h/.cpp files in one library and you can export many symbols, too.

    Try giving "Add" another name or putting it into a namespace. Maybe some other library is already exporting a "Add"-symbol and you get a conflict... which will be resolved one way or the other with only one of the implementations being used. That can trigger all kinds of strange effects:)

    In general you only need to export/import a symbol in the header file, too, so consider to remove the QTSHAREDLIBSHARED_EXPORT from the .cpp file.

    [EDIT: fixed strike-through markup, Volker]

  • I have tried:

    Change 'Add' to 'MyAdd'

    Remove QTSHAREDLIBSHARED_EXPORT from the .cpp file.

    But same error.

  • Finally I got it!

    the dll library project folder:

    the build folder:

    the widget application project folder:

    the widget application build folder:

    In the widget application .pro file:
    LIBS += C:/Qt_Test/QtSharedLib-build-desktop/debug/QtSharedLib.lib

    If I copy the dll file to the folder:

    So question is: how to set dll path in .pro file?

  • It seems no way to set dll library path inside .pro. Anyway, I could set PATH in windows environment so that exe will use to find the dll path.

Log in to reply

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.