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 :)