Abstract plugin inheritance error

[Defohin]

@kshegunov I tried to add this:

myprojectglobal.h

#ifndef MYPROJECTGLOBAL_HPP
#define MYPROJECTGLOBAL_HPP

#include <QtCore/qglobal.h>

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

#endif // MYPROJECTGLOBAL_HPP

myproject.pro

DEFINES += MYPROJECT_LIBRARY

plugininterface.hpp

#ifndef PLUGININTERFACE_HPP
#define PLUGININTERFACE_HPP

#include "myprojectglobal.hpp"
#include <QtPlugin>

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

#define PluginInterface_iid "PluginInterface/1.0"

Q_DECLARE_INTERFACE(PluginInterface, PluginInterface_iid)

#endif // PLUGININTERFACE_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

And now I'm getting these errors:

moc_pluginfoo.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl PluginInterface::~PluginInterface(void)" (_imp??1PluginInterface@@UEAA@XZ) referenced in function "int public: __cdecl PluginFoo::PluginFoo(void)'::1'::dtor$0" (?dtor$0@?0???0PluginFoo@@QEAA@XZ@4HA)

moc_pluginfoo.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl PluginInterface::PluginInterface(void)" (_imp??0PluginInterface@@QEAA@XZ) referenced in function "public: __cdecl PluginFoo::PluginFoo(void)" (??0PluginFoo@@QEAA@XZ)

moc_pluginfoo.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual void * __cdecl AbstractPlugin::qt_metacast(char const *)" (_imp?qt_metacast@AbstractPlugin@@UEAAPEAXPEBD@Z) referenced in function "public: virtual void * __cdecl PluginFoo::qt_metacast(char const *)" (?qt_metacast@PluginFoo@@UEAAPEAXPEBD@Z)

moc_pluginfoo.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual int __cdecl AbstractPlugin::qt_metacall(enum QMetaObject::Call,int,void * *)" (_imp?qt_metacall@AbstractPlugin@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z) referenced in function "public: virtual int __cdecl PluginFoo::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@PluginFoo@@UEAAHW4Call@QMetaObject@@HPEAPEAX@Z)

moc_pluginfoo.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl AbstractPlugin::AbstractPlugin(void)" (_imp??0AbstractPlugin@@QEAA@XZ) referenced in function "public: __cdecl PluginFoo::PluginFoo(void)" (??0PluginFoo@@QEAA@XZ)

moc_pluginfoo.obj:-1: error: LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl AbstractPlugin::~AbstractPlugin(void)" (_imp??1AbstractPlugin@@UEAA@XZ) referenced in function "public: virtual __cdecl PluginFoo::~PluginFoo(void)" (??1PluginFoo@@UEAA@XZ)

moc_pluginfoo.obj:-1: error: LNK2001: unresolved external symbol "__declspec(dllimport) public: static struct QMetaObject const AbstractPlugin::staticMetaObject" (_imp?staticMetaObject@AbstractPlugin@@2UQMetaObject@@B)

....\bin\plugins\pluginfoo.dll:-1: error: LNK1120: 7 unresolved externals

[jsulm]

@Defohin Do you link your pluginfoo plugin against the lib containing AbstractPlugin and PluginInterface?

[Defohin]

@jsulm What you mean? The whole code I have is here.

[SGaist]

Hi,

The usual setup when building a plugin based application is to have the plugin interfaces definitions and related code in a library that you will link to both the plugin and the application.

That's what is suggested here.

[Defohin]

@SGaist I'm really struggling to understand, can you provide an example, please?

[SGaist]

Roughly :
pluginfoo.pro

QT          += core gui
TARGET       = pluginfoo
TEMPLATE     = lib
CONFIG      += plugin
DESTDIR      = $$OUTPWD/bin/plugins
LIBS += -L$$OUTPWD/lib -lmycoollib
DEFINES     += QT_DEPRECATED_WARNINGS
INCLUDEPATH += ../mycoollib
SOURCES     += pluginfoo.cpp
HEADERS     += pluginfoo.hpp
DISTFILES   += pluginfoo.json

mycoollib.pro

QT          += core gui
TARGET       = mycoollib
TEMPLATE  = lib
DESTDIR      = $$OUTPWD/lib
INCLUDEPATH += .
SOURCES     += \
    abstractplugin.cpp
HEADERS     += \
    plugininterface.hpp
    abstractplugin.hpp

myproject.pro

QT      += core gui widgets xml network
TARGET   = myproject
TEMPLATE = app
DESTDIR  = $$OUTPWD/bin
LIBS += -L$$OUTPWD/lib -lmycoollib
INCLUDEPATH += ../mycoollib
DEFINES += QT_DEPRECATED_WARNINGS
SOURCES += src/main.cpp \
           gui/myprojectwindow.cpp

HEADERS += gui/myprojectwindow.hpp

Project structure

mycoolproject \
---- mycoollib
---- pluginfoo
---- myproject

mycoolproject being a SUBDIR project building first mycoollib and then pluginfoo and myproject.

[Defohin]

@SGaist Do I have to link with -l every single plugin I have? Or I can just provide a path like -L and it's going to work?

I will try to modify here based on your example.

[SGaist]

You don't link the plugins. You link your plugins against that common library.

Yes, you have to use both -land -L.

-L just tells the linker where to look at.

[Defohin]

@SGaist It works, but I have another question now.

I named the "commonlib" to "pluginmanager" this class will hold information about plugins, load, unload and so on using QPluginLoader, but... when I try to use it on the main application including the header pluginmanager.hpp it says that it cannot open the file, even if I have the INCLUDEPATH += ../pluginmanager. On Qt Creator it does work, I'm able to ctrl+click, etc, but when I try to compile I get this error.

[jsulm]

@Defohin Did you run qmake again after changing the pro file? After qmake you should do a complete rebuild.

[Defohin]

@jsulm It works, but now I'm getting unresolved external symbol on the main project when trying to use PluginManager manager on the MyProjectWindow, and I have LIBS += -L../libs -lpluginmanager on the pro file.

myprojectwindow.obj:-1: error: LNK2019: unresolved external symbol "public: __cdecl PluginManager::PluginManager(class QObject *)" (??0PluginManager@@QEAA@PEAVQObject@@@Z) referenced in function "public: __cdecl MyProjectWindow::MyProjectWindow(class QWidget *)" (??0MyProjectWindow@@QEAA@PEAVQWidget@@@Z)

[jsulm]

@Defohin ../libs is a relative path, are you sure it is correct?
Can you post the compiler/linker call just before the error message?
As suggested by @SGaist : LIBS += -L$$OUTPWD/lib -lmycoollib (pluginmanager instead of mycoollib)

[Defohin]

@jsulm I'm using $$OUTPWD now but it still doesn't work.

[jsulm]

@Defohin Is the resulting path correct and is the lib there?

[Defohin]

It's working now, I forgot to put MYPROJECT_EXPORT on PluginManager class.

I love you guys ♥