undefined reference to qt_static _plugin

NIXIN

Hi,

I am trying to load a static plugin in Qt for which I have tried the below code. My project name is "static_plugin_qmake".
I am creating a static plugin called "plugin_qmake" and trying to load it through a application "launcher"

static_plugin_qmake.pro

TEMPLATE = subdirs

SUBDIRS  = plugin_qmake \
                 launcher


launcher.pro

TEMPLATE = app
QT      += widgets

HEADERS  = interface.h

SOURCES += main.cpp

LIBS    += "/home/uidm9805/Qt Projects/static_plugin_qmake/build/plugin_qmake/libplugin_qmake.a"

interface.h

#ifndef INTERFACE_H
#define INTERFACE_H

#include <QtPlugin>

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

    virtual void setValue(int value) = 0;

    virtual int getValue() = 0;
};

#define Interface_iid "interface_identifier_id"
Q_DECLARE_INTERFACE(Interface, Interface_iid)

#endif // INTERFACE_H

main.cpp

#include <QApplication>
#include <QtPlugin>

#include <QDebug>

Q_IMPORT_PLUGIN(plugin_qmake)

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

    qDebug() << "Hello World";

    return app.exec();
}

plugin_qmake.pro

TEMPLATE      = lib
CONFIG       += plugin static
QT           += widgets

INCLUDEPATH  += ../..

HEADERS       = pluginqmake.h

SOURCES       = pluginqmake.cpp

TARGET        = $$qtLibraryTarget(plugin_qmake)

pluginqmake.h

#ifndef PLUGINQMAKE_H
#define PLUGINQMAKE_H

#include <QObject>
#include <QtPlugin>

#include "../launcher/interface.h"

class PluginQmake : public QObject,
                    public Interface
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID Interface_iid)
    Q_INTERFACES(Interface)

 public:
    void setValue(int value);

    int getValue();

private:
    int mValue;
};

#endif // PLUGINQMAKE_H

pluginqmake.cpp

#include "pluginqmake.h"

void PluginQmake::setValue(int value)
{
    mValue = value;
}

int PluginQmake::getValue()
{
    return mValue;
}

But when I build this project, I get following errors:

/home/uidm9805/Qt Projects/static_plugin_qmake/launcher/main.cpp:6: error: undefined reference to 'qt_static_plugin_plugin_qmake()'
collect2: error: ld returned 1 exit status

I don't understand why I am getting this error? I need help to make it work.....

jsulm

@NIXIN I think you forgot "QTPLUGIN += " in your pro file as described here: http://doc.qt.io/qt-5/plugins-howto.html#static-plugins

NIXIN

@jsulm what should I add with QTPLUGIN +=

because I am creating my own plugin

jsulm

@NIXIN Sorry, my post was wrong.
"Link your application with your plugin library using LIBS in the .pro file." - so, using LIBS is correct. But you're using it wrongly, it should be:

LIBS    += -L"/home/uidm9805/Qt Projects/static_plugin_qmake/build/plugin_qmake" -lplugin_qmake

Better to use relative paths, see http://doc.qt.io/qt-5/qtwidgets-tools-plugandpaint-app-example.html

NIXIN

@jsulm I tried using LIBS += the way you suggested, however still it is not working...
getting same errors again

jsulm

@NIXIN Can you show your LIBS line from your pro file?

NIXIN

@jsulm

TEMPLATE = app
QT      += widgets

HEADERS  = interface.h

SOURCES += main.cpp

#LIBS    += "/home/uidm9805/Qt Projects/static_plugin_qmake/build/plugin_qmake/libplugin_qmake.a"

LIBS    += -L"/home/uidm9805/Qt Projects/static_plugin_qmake/build/plugin_qmake" -lplugin_qmake

jsulm

@NIXIN You should check the linker call as you have a space in your path which can cause issues (you should avoid spaces in paths).

NIXIN

@jsulm I tried same thing with this example http://doc.qt.io/qt-5/qtwidgets-tools-plugandpaint-app-example.html and its working fine there

LIBS += "/home/uidm9805/Qt Projects/plugandpaint/build/plugandpaint/plugins/libpnp_basictools.a"

don't know why this project is behaving in odd manner

jsulm

@NIXIN Is your plug-in really located here: /home/uidm9805/Qt Projects/static_plugin_qmake/build/plugin_qmake? And was it build with exact same compiler and Qt version?

NIXIN

@jsulm yes plugin is located in the given path and compiler versions are same

NIXIN

can anybody help me with this issue??

NIXIN

After lot of hit and trial, I got the mistake I was doing

Q_IMPORT_PLUGIN(plugin_qmake)

this line should have the class name of plugin

Q_IMPORT_PLUGIN(PluginQmake)

now it works fine....

Ni.Sumi

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