Inconsistent dll linkage

SGaist

Hi,

Did you properly define MYPROJECT_LIBRARY when building the library and not when using it ?

Defohin

@SGaist Yes, DEFINES += CORE_LIBRARY in the core library and DEFINES += PLUGINMANAGER_LIBRARY in the pluginmanager.

SGaist

Can you exactly how your project is organised ?

Defohin

@SGaist https://forum.qt.io/topic/75042/abstract-plugin-inheritance-error/14

I created another library called core that is not listed there and create the core_global.hpp, tried to include that header on the pluginmanager and I get the errors... - core_global.hpp has the same content as pluginmanager_global.hpp but it only works with it, not with core_global.hpp.

dheerendra

Check if your plugin class inherited from QObject and Q_OBJECT is included in private section

Defohin

@dheerendra I don't think that it has anything to do with the plugins, and the plugins doesn't inherent from QObject cause AbstractPlugin does that already and if I make a plugin inherent from QObject as well the compiler throws me a warning saying that the two of them is inheriting the same class.

SGaist

Did you adjust the define value when changing the header ?

Defohin

@SGaist Yes, I did, both the files are exactly equal, the only thing that changes is CORE_LIBRARY and PLUGINMANAGER_LIBRARY, and they are both defined on their related pro files. I just can't use the header from one library on the other one and these errors happen.

SGaist

What do you mean by you can't use the header ? What exactly goes wrong ?

Defohin

@SGaist I get the errors mentioned above about inconsistent dll linkage.

I'm going to post the entire working code and then I will post the change so you can see what is going on.

Here is the link to download the entire project: download

That is how the structure looks like:

|-- myproject
    |-- myproject.pro
    |-- core
    |   |-- core.pro
    |   |-- core_global.hpp
    |-- myproject
    |   |-- main.cpp
    |   |-- myproject.pro
    |   |-- myprojectwindow.cpp
    |   |-- myprojectwindow.hpp
    |-- pluginmanager
    |   |-- abstractplugin.cpp
    |   |-- abstractplugin.hpp
    |   |-- plugininterface.hpp
    |   |-- pluginmanager.cpp
    |   |-- pluginmanager.hpp
    |   |-- pluginmanager.pro
    |   |-- pluginmanager_global.hpp
    |-- plugins
        |-- plugins.pro
        |-- pluginfoo
            |-- pluginfoo.cpp
            |-- pluginfoo.hpp
            |-- pluginfoo.json
            |-- pluginfoo.pro

myproject.pro

TEMPLATE = subdirs
SUBDIRS  = core \
           pluginmanager \
           plugins \
           myproject
CONFIG  += ordered

core.pro

QT      += core
TARGET   = core
TEMPLATE = lib
DEFINES += CORE_LIBRARY

DESTDIR  = $$OUTPWD/bin

HEADERS += core_global.hpp

core_global.hpp

#ifndef CORE_GLOBAL_HPP
#define CORE_GLOBAL_HPP

#include <QtCore/qglobal.h>

#if defined(CORE_LIBRARY)
#  define MYPROJECT_EXPORT Q_DECL_EXPORT
#else
#  define MYPROJECT_EXPORT Q_DECL_IMPORT
#endif

#endif // CORE_GLOBAL_HPP

main.cpp

#include "myprojectwindow.hpp"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication application(argc, argv);

    MyProjectWindow window;
    window.show();

    return application.exec();
}

myproject.pro

QT      += core gui widgets xml network
TARGET   = myproject
TEMPLATE = app
DEFINES += QT_DEPRECATED_WARNINGS
DEFINES += MYPROJECT_LIBRARY

INCLUDEPATH += ../core ../pluginmanager
DESTDIR      = $$OUTPWD/bin
LIBS        += -L$$OUTPWD/bin -lcore -lpluginmanager

HEADERS   += myprojectwindow.hpp
SOURCES   += main.cpp \
             myprojectwindow.cpp

myprojectwindow.cpp

#include "myprojectwindow.hpp"

MyProjectWindow::MyProjectWindow(QWidget *parent) : QMainWindow(parent)
{

}

myprojectwindow.hpp

#ifndef MYPROJECTWINDOW_HPP
#define MYPROJECTWINDOW_HPP

#include <QMainWindow>

class MyProjectWindow : public QMainWindow
{
    Q_OBJECT

public:
    MyProjectWindow(QWidget *parent = 0);
};

#endif // MYPROJECTWINDOW_HPP

abstractplugin.cpp

#include "abstractplugin.hpp"

abstractplugin.hpp

#ifndef ABSTRACTPLUGIN_HPP
#define ABSTRACTPLUGIN_HPP

#include "plugininterface.hpp"

class MYPROJECT_EXPORT AbstractPlugin : public QObject, public PluginInterface
{
    Q_OBJECT
    Q_INTERFACES(PluginInterface)
};

#endif // ABSTRACTPLUGIN_HPP

plugininterface.hpp

#ifndef PLUGININTERFACE_HPP
#define PLUGININTERFACE_HPP

#include "pluginmanager_global.hpp"
#include <QObject>

class MYPROJECT_EXPORT PluginInterface
{
public:
    virtual ~PluginInterface() {}
};

#define PluginInterface_iid "PluginInterface/1.0"

Q_DECLARE_INTERFACE(PluginInterface, PluginInterface_iid)

#endif // PLUGININTERFACE_HPP

pluginmanager.cpp

#include "pluginmanager.hpp"

PluginManager::PluginManager(QObject *parent) : QObject(parent)
{

}

pluginmanager.hpp

#ifndef PLUGINMANAGER_HPP
#define PLUGINMANAGER_HPP

#include "pluginmanager_global.hpp"
#include <QObject>

class MYPROJECT_EXPORT PluginManager : public QObject
{
    Q_OBJECT

public:
    explicit PluginManager(QObject *parent = 0);
};

#endif // PLUGINMANAGER_HPP

pluginmanager.pro

QT      += core
TARGET   = pluginmanager
TEMPLATE = lib
DEFINES += PLUGINMANAGER_LIBRARY

INCLUDEPATH += ../core
DESTDIR      = $$OUTPWD/bin

SOURCES += abstractplugin.cpp \
           pluginmanager.cpp
HEADERS += pluginmanager_global.hpp \
           abstractplugin.hpp \
           pluginmanager.hpp \
           plugininterface.hpp

pluginmanager_global.hpp

#ifndef PLUGINMANAGER_GLOBAL_HPP
#define PLUGINMANAGER_GLOBAL_HPP

#include <QtCore/qglobal.h>

#if defined(PLUGINMANAGER_LIBRARY)
#  define MYPROJECT_EXPORT Q_DECL_EXPORT
#else
#  define MYPROJECT_EXPORT Q_DECL_IMPORT
#endif

#endif // PLUGINMANAGER_GLOBAL_HPP

plugins.pro

TEMPLATE = subdirs
SUBDIRS  = pluginfoo

pluginfoo.cpp

#include "pluginfoo.hpp"

pluginfoo.hpp

#ifndef PLUGINFOO_HPP
#define PLUGINFOO_HPP

#include "abstractplugin.hpp"

class PluginFoo : public AbstractPlugin
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID PluginInterface_iid FILE "pluginfoo.json") \
    Q_INTERFACES(PluginInterface)
};

#endif // PLUGINFOO_HPP

pluginfoo.json

{}

pluginfoo.pro

QT          += core gui
TARGET       = pluginfoo
TEMPLATE     = lib
CONFIG      += plugin
DEFINES     += QT_DEPRECATED_WARNINGS

INCLUDEPATH += ../../core ../../pluginmanager
DESTDIR      = $$OUTPWD/bin/plugins
LIBS        += -L$$OUTPWD/bin -lcore -lpluginmanager

SOURCES     += pluginfoo.cpp \
               pluginfoo.cpp
HEADERS     += pluginfoo.hpp \
               pluginfoo.hpp
DISTFILES   += pluginfoo.json

The error happens if I change this:

plugininterface.hpp

from:

#include "pluginmanager_global.hpp"

to:

#include "core_global.hpp"

debug\moc_abstractplugin.cpp:56: warning: C4273: 'AbstractPlugin::qt_static_metacall': inconsistent dll linkage

debug\moc_abstractplugin.cpp:63: warning: C4273: 'staticMetaObject': inconsistent dll linkage

debug\moc_abstractplugin.cpp:63: error: C2491: 'AbstractPlugin::staticMetaObject': definition of dllimport static data member not allowed

debug\moc_abstractplugin.cpp:70: warning: C4273: 'AbstractPlugin::metaObject': inconsistent dll linkage

debug\moc_abstractplugin.cpp:75: warning: C4273: 'AbstractPlugin::qt_metacast': inconsistent dll linkage

debug\moc_abstractplugin.cpp:87: warning: C4273: 'AbstractPlugin::qt_metacall': inconsistent dll linkage

Yes, I tried qmake but it doesn't work either.

Defohin

Anyone knows how to solve this?

SGaist

If you want to use the same export macros everywhere you also have to modify the DEFINES everywhere.

Defohin

@SGaist I tried what you said and it worked. But I have a question, do you think that it's right doing that way? I don't want to be repeating code as I was doing. Is there a better way or it's just fine?

SGaist

Having a per library global header with the export macros even if it seems redundant is cleaner.

Defohin

@SGaist Thank you, I'll keep the original structure then.

Oliver Broad

This seems to be the top search result for this warning so I'd like to add a note relating to a case I've found.

I've cloned and built the open-source project "qModMaster", and this warning comes up a lot.

What appears to have happened is that the library "libmodbus" is statically linked into qModMaster, but the libmodbus source assumes it will be implemented as a DLL, so the warnings come up every time it attempts to import/export a function. I believe the inconsistency is that it has both a definition for the function and a directive to import the function.

. #if defined(_MSC_VER)
. # if defined(DLLBUILD)
. /* define DLLBUILD when building the DLL */
. # define MODBUS_API __declspec(dllexport)
. # else
. # define MODBUS_API __declspec(dllimport)
. # endif

In this case the library has been modified after adding it to the project, it isn't a clone so in the short term it is easiest to just define MODBUS_API as nothing.

SGaist

@Oliver-Broad said in Inconsistent dll linkage:

qModMaster

Hi and welcome to devnet,

Which version of qModMaster are you talking about ?

From a quick search, the only thing I have found is that libmodbus is a C library so it is not concerned by these export/import considerations and qModMaster does not use it as a library but compiles the sources it uses directly into the executable.