undefined reference in a shared class between plugin and app.

[Filipe Antunes]

Hi all,
I want to use a class shared between plugins and a main app.
But when I try to compil, I have this error:

plugins\plugin01\plugin01.cpp:13: erreur : undefined reference to `CommonParameter::CommonParameter()'

I must have a LIBS problem somewhere in a .pro file or something else

Thanks in advance,
Filipe

Code:

/testplugin.pro

TEMPLATE = subdirs
SUBDIRS += \
    src \
    plugins

/src/src.pro

TARGET          = testplugin
DESTDIR         = ../bin
TEMPLATE        = app
QT    	       -= gui
HEADERS += \
    iplugin.h \
    commonparameter.h
SOURCES += \
    main.cpp \
    commonparameter.cpp

qtHaveModule(uitools):!embedded: QT += uitools
else: DEFINES += QT_NO_UITOOLS

build_all:!build_pass {
    CONFIG -= build_all
    CONFIG += release
}
CONFIG   += console
CONFIG   -= app_bundle

/src/iplugin.h

#ifndef IPLUGIN_H
#define IPLUGIN_H

#include <QtPlugin>
#include <commonparameter.h>

class QString;

class IPlugin
{
public:
    virtual ~IPlugin() {}

    virtual QString name() const = 0;
    virtual CommonParameter *parameter() = 0;
};

#define IPlugin_iid "AntunesFilipe.TestPlugin.IPlugin"
Q_DECLARE_INTERFACE(IPlugin, IPlugin_iid)

#endif // IPLUGIN_H

/src/main.cpp

#include <QCoreApplication>
#include <QTextStream>
#include <QDir>
#include <QPluginLoader>
#include "iplugin.h"
#include "commonparameter.h"
int main(int argc, char *argv[])
{    
   QCoreApplication app(argc, argv);

    // Find plugins located in a repository folder and load them...
    QDir pluginsDir = QDir(qApp->applicationDirPath());
    pluginsDir.cd("plugins");
    foreach (QString fileName, pluginsDir.entryList(QDir::Files)) {
        QPluginLoader loader(pluginsDir.absoluteFilePath(fileName));
        QObject *plugin = loader.instance();
        if (plugin) {
            IPlugin *iPlugin = qobject_cast<IPlugin *>(plugin);
            if (iPlugin) {
                QTextStream(stdout) << "> Plugin name:" << iPlugin->name() << endl;

                // !!! Waiting for: Fix undefined reference to CommonParameter::CommonParameter()
                // CommonParameter *param = plugin->parameter();
                // QTextStream(stdout) << "         user:" << param->userName() << endl;
                // QTextStream(stdout) << "     password:" << param->password() << endl;
            }
        }
    }

    return 0;
}

Here the "sharded" class:
/src/commonparameter.h

#ifndef COMMONPARAMETER_H
#define COMMONPARAMETER_H
#include <QString>
class CommonParameter
{
public:
    CommonParameter();
    void setUserName(const QString& name);
    void setPassword(const QString& password);
    QString userName() const;
    QString password() const;
private:
    QString m_userName;
    QString m_password;
};
#endif // COMMONPARAMETER_H

/src/commonparameter.cpp

#include "commonparameter.h"
CommonParameter::CommonParameter(){}
void CommonParameter::setUserName(const QString& name)
{
    m_userName = name;
}
void CommonParameter::setPassword(const QString& password)
{
    m_password = password;
}
QString CommonParameter::userName() const
{
    return m_userName;
}
QString CommonParameter::password() const
{
    return m_password;
}

And a plugin:
/plugins.pro

TEMPLATE = subdirs
SUBDIRS += \
    plugin01 \

/plugins/plugin01/plugin01.pro

TEMPLATE      = lib
CONFIG       += plugin
QT           += widgets
INCLUDEPATH  += ../../src
HEADERS += plugin01.h
SOURCES += plugin01.cpp
TARGET        = $$qtLibraryTarget(plugin01)
DESTDIR       = ../../bin/plugins

/plugins/plugin01/plugin01.h

#ifndef PLUGIN01_H
#define PLUGIN01_H
#include <QObject>
#include <QtPlugin>
#include <iplugin.h>
class Plugin01 : public QObject, IPlugin
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "AntunesFilipe.TestPlugin.Plugin01.IPlugin" FILE "plugin01.json")
    Q_INTERFACES(IPlugin)
public:
    Plugin01();
    QString name() const Q_DECL_OVERRIDE;
    CommonParameter *parameter() Q_DECL_OVERRIDE;
};
#endif // PLUGIN01_H

/plugins/plugin01/plugin01.cpp

#include "plugin01.h"
#include <QWidget>

Plugin01::Plugin01(){}

QString Plugin01::name() const
{
    return QString ("My Plugin 01");
}

CommonParameter *Plugin01::parameter()
{
    CommonParameter *param = new CommonParameter(); // ?!? <-- undefined reference to `CommonParameter::CommonParameter()'
    param->setUserName(QString ("TEST"));
    param->setPassword(QString ("123456"));

    return param;
}

[SGaist]

Hi and welcome to devnet,

Did you base your application on the echo plugin example ?

[Filipe Antunes]

Hi SGaist

Yes I have based my application on echo plugin and Plug & Paint example.

Under windows with mingw, I can not compile the project, I have this message:

plugins\plugin01\plugin01.cpp:13: erreur : undefined reference to `CommonParameter::CommonParameter()'

Under linux, with g++(4.8.5) the compilation is done but when I execute, I have this message:

./testplugin: symbol lookup error: ???/plugins/libplugin01.so: undefined symbol: _ZN15CommonParameterC1Ev

In my first post, I made a mistake in the copy of the code:

src/main.cpp
-- CommonParameter * param = plugin->parameter();
has to be replaced by
++ CommonParameter * param = iPlugin->parameter();

[Filipe Antunes]

I am not sure of my "hack" but..it works if I add this line in my .pro application:

QMAKE_LFLAGS   += -rdynamic

But Why ?!?

[SGaist]

The problem you are having is that you are using a class that must be known to both your application and plugin. The clean way to do that is to have a library implementing the stuff that is used in both and link each to it.

Basically add another sub-project for a library that will contain CommonParameter.

[Filipe Antunes]

Thank You SGaist
I think I will keep my current "dirty way", after all my application is the common module.

[Filipe Antunes]

Well...I confirm. It is necessary to cut the application in sub-project.
-rdynamic is not supported by OSX and Windows (!= ELF format)

[kshegunov]

@Filipe-Antunes said in undefined reference in a shared class between plugin and app.:

-rdynamic is not supported by OSX and Windows (!= ELF format)

As is expected. The ABI on Windows is different enough and symbol resolution is done at link-time so it couldn't work. Follow @SGaist's advice and export the common classes from a library; that's the reason libraries were invented in the first place.

Kind regards.