Using Qt lib macros with static libs and apps

[btse]

Hi, I've run into a situation that I'm not quite sure how to resolve. Here is the scenario:

I have a static lib, let's call it glib.
In glib I have 2 files called app.hpp and app.cpp.
Inside of these files are subclasses of QApplication and QCoreApplication.
I want to be able to use the subclasses of QCoreApplication inside of apps that do not have the Qt GUI framework ( QT -= gui), i.e command line apps.

I now have a cmd line app called capp.
Inside of capp, I want to use my custom subclasses of QCoreApplication.
So I #include <app.hpp> and add the necessary lib to my cmd line app's project file.

However, because this is a cmd line app ( QT -= gui), it of course complains that <QApplication> does not exist.
So in an attempt to resolve this, I wrapped all of the "GUI" related code in app.hpp and app.cpp with a QT_GUI_LIB macro ifdef.

Keep in mind that app.hpp and app.cpp is compiled as a static lib. That means that the generated static lib still contains all the symbols for the subclasses of both QApplication and QCoreApplication, since the lib itself is compiled with QT += gui widgets

I can of course split up the GUI and non-gui code into 2 separate files, but wanted to know if my current approach should work and if I'm just doing something incorrectly.

Thanks for any help

[SGaist]

Hi,

Can you show your header content ?

Note that it's indeed better to have these two classes in separate headers. That will makes things way clearer when using your library.

[btse]

So the static lib builds perfectly fine. I've also tried using the QT_GUI_LIB macro instead but same result. I get these compile errors when trying to use the static lib in a non-gui app. Perhaps the easiest solution is to just spit up the GUI and non-GUI code into separate files.

This is what my app's project file looks like:

LIBS_DEPTH = ../..
LIB_DEPENDENCIES = \
   momalib \
   gedilib \
   gselib \
   tools \
   gse_streams
include(../../custom.pri)

# Input
HEADERS += mainclass.hpp
SOURCES += main.cpp mainclass.cpp

CONFIG += qt console
CONFIG -= app_bundle
QT -= gui
QT += network

Generated compile error:

Undefined symbols for architecture x86_64:
  "QApplication::qt_metacall(QMetaObject::Call, int, void**)", referenced from:
      vtable for ExceptionSafeApplication in libgselib.a(apputil.o)
      NasaApp::qt_metacall(QMetaObject::Call, int, void**) in libgselib.a(moc_apputil.o)
  "QApplication::qt_metacast(char const*)", referenced from:
      vtable for ExceptionSafeApplication in libgselib.a(apputil.o)
      NasaApp::qt_metacast(char const*) in libgselib.a(moc_apputil.o)
  "QApplication::compressEvent(QEvent*, QObject*, QPostEventList*)", referenced from:
      vtable for ExceptionSafeApplication in libgselib.a(apputil.o)
      vtable for NasaApp in libgselib.a(moc_apputil.o)
  "QApplication::staticMetaObject", referenced from:
      NasaApp::staticMetaObject in libgselib.a(moc_apputil.o)
  "QApplication::event(QEvent*)", referenced from:
      vtable for ExceptionSafeApplication in libgselib.a(apputil.o)
      vtable for NasaApp in libgselib.a(moc_apputil.o)
  "QApplication::notify(QObject*, QEvent*)", referenced from:
      ExceptionSafeApplication::notify(QObject*, QEvent*) in libgselib.a(apputil.o)
      vtable for NasaApp in libgselib.a(moc_apputil.o)
  "QApplication::QApplication(int&, char**, int)", referenced from:
      NasaApp::NasaApp(int&, char**, int, int, int, QString) in libgselib.a(apputil.o)
      ExceptionSafeApplication::ExceptionSafeApplication(int&, char**) in libgselib.a(apputil.o)
  "QApplication::~QApplication()", referenced from:
      NasaApp::NasaApp(int&, char**, int, int, int, QString) in libgselib.a(apputil.o)
      ExceptionSafeApplication::~ExceptionSafeApplication() in libgselib.a(apputil.o)
      NasaApp::~NasaApp() in libgselib.a(moc_apputil.o)
  "QApplication::metaObject() const", referenced from:
      vtable for ExceptionSafeApplication in libgselib.a(apputil.o)
  "typeinfo for QApplication", referenced from:
      typeinfo for ExceptionSafeApplication in libgselib.a(apputil.o)
      typeinfo for NasaApp in libgselib.a(moc_apputil.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

And the static lib's header file:

/**
 * @file
 */

#ifndef APPUTIL_HPP
#define APPUTIL_HPP

#include <logger/logger.hpp>
#include <util/pluginmanager.hpp>

#ifdef QT_WIDGETS_LIB
#include <QApplication>
#else
#include <QCoreApplication>
#endif
#include <QPointer>


bool disableAppNap(const QString &appDomainName);


/*******************************************************************************
 * Almost all projects should use one of the below app subclasses. They enforce
 * routine initialization and conventions.
 ******************************************************************************/

/**
 * Use for non-GUI apps.
 */
class NasaCoreApp : public QCoreApplication
{
   Q_OBJECT
public:
   explicit NasaCoreApp(int & ac,
                        char **av,
                        int majorVer,
                        int minorVer,
                        int patchVer,
                        QString svnRevision);

   void initializeLogger(bool stdErrEnabled = false);

private:
   Q_DISABLE_COPY(NasaCoreApp)
};


#ifdef QT_WIDGETS_LIB



/**
 * Use for GUI apps.
 */
class NasaApp : public QApplication
{
   Q_OBJECT
public:
   explicit NasaApp(int & ac,
                    char **av,
                    int majorVer,
                    int minorVer,
                    int patchVer,
                    QString svnRevision);

   void initializeLogger(bool stdErrEnabled = false);
   void initializeConfig699(const QString & group = "");

   void loadPlugins(const QStringList & pluginPaths = QStringList());
   PluginManager *pluginManager() { return pluginManager_; }

private:
   Q_DISABLE_COPY(NasaApp)

   QPointer<PluginManager> pluginManager_;
};


/**
 * Provides a QApplication that catches any exceptions that are thrown during
 * handling of any events. The intention is to prevent the application from
 * crashing due to an exception.
 */
class ExceptionSafeApplication : public QApplication
{
public:
   explicit ExceptionSafeApplication(int & ac, char **av);

   virtual bool notify (QObject *r, QEvent *e );

private:
   Q_DISABLE_COPY(ExceptionSafeApplication)
};

#endif // QT_WIDGETS_LIB

#endif // APPUTIL_HPP

[Christian Ehrlicher]

Wouldn't it be easier to simply create two separate classes/libraries instead?

[btse]

@Christian-Ehrlicher

Yes and that's what I've already done. I was really more curious if my original approach should have worked, but apparently there's holes in my understanding of how header and lib files interact.

[Christian Ehrlicher]

You have to make sure QT_WIDGETS_LIB is (not) defined when using the header. So I assume QT_WIDGETS_LIB was defined when you wanted to use it in non-gui mode.

[btse]

@Christian-Ehrlicher Well I've explicitly added "QT -= gui widgets" to my non-gui app's project file but it still complains about missing symbols. Is that not enough?

[Christian Ehrlicher]

@Christian-Ehrlicher said in Using Qt lib macros with static libs and apps:

QT_WIDGETS_LIB

I would check it with a short '#error QT_WIDGETS_LIB defined' within the #ifdef QT_WIDGETS_LIB branch while compiling to non-gui app just to be sure :)