qt - Using QSettings in a global static class -

my task create qsettings wrapper class (wrapping needed qml) can reach everywhere model, too.

the obvious choice static global instance of class. problem approach it's destroyed after main, after qapplication destroyed, giving me following warning:

qapplication::qappname: please instantiate qapplication object first

here simplified, sample code showing simple wrapper, , destruction phases:

#include <qcoreapplication> #include <qdebug> #include <qglobalstatic> #include <qsettings> #include <qtimer>  class settings: public qobject { public:     ~settings() { qdebug() << "~settings"; }     qsettings settings; };  q_global_static(settings, globalsettings)  int main(int argc, char *argv[]) {     qcoreapplication app(argc, argv);      qobject::connect(&app, &qcoreapplication::abouttoquit, [](){qdebug() << "~qcoreapplication abouttoquit";});     qobject::connect(&app, &qcoreapplication::abouttoquit, [](){globalsettings->settings.setvalue("hi", 2);});     qobject::connect(&app, &qcoreapplication::destroyed, [](){qdebug() << "~qcoreapplication destroyed";});      qtimer::singleshot(0, &app, slot(quit()));      return app.exec(); } 

it prints out following:

~qcoreapplication abouttoquit ~qcoreapplication destroyed ~settings qapplication::qappname: please instantiate qapplication object first 

my question is: providing, in program qsettings used after qcoreapplication::abouttoquit emitted before qcoreapplication::destroyed, how can avoid warning?

using qsettings

i've used qsettings in pretty every project i've ever made. here pattern tend use it:

in main.cpp

#include <qsettings>  //...  // in main(), after qapplication instantiated, before settings accessed  qsettings::setdefaultformat(qsettings::iniformat); qapplication::setorganizationname("myorg"); qapplication::setapplicationname("myapp"): 

then anytime access qsettings, this:

qsettings s;  s.value(// reading value s.setvalue(// writing value 

everything gets saved in user scope in ini text file. located in windows under c:/users/<username>/appdata/roaming/myorg/myapp.ini.

this usage of qsettings (imho) clean, doesn't require global variables or static references , fast , efficient. , readable.

now able have things load settings @ right times, , not errors mentioned in question, see initial example in links below:

http://doc.qt.io/qt-5/qsettings.html#restoring-the-state-of-a-gui-application

http://doc.qt.io/qt-5/qtwidgets-mainwindows-application-example.html

it works better in timeline of qt application , works great. tend make readsettings , writesettings of gui classes , number of backend classes. readsettings happens when widget has showevent or constructor happen , writesettings happens in closeevent. if have dedicated settings dialog, emit signal have affected classes readsettings, right after settings dialog writes specific settings.

if use qml port of qsettings, uses organization name , application name , default format of qsettings pick filename , location.

http://doc.qt.io/qt-5/qml-qt-labs-settings-settings.html

i believe default functionality of qml component read setting when component created, , write setting whenever qml changes it. change c++ , have recognized qml, should use standard qml/c++ methods out there such as:

http://doc.qt.io/qt-5/qtqml-cppintegration-topic.html

and lastly if planning on installing defaults program decided build , don't want hardcode them, hand write ini file , have installer place in system scope location: c:/programdata/myorg/myapp.ini

and in case settings of program more complex want store in ini file, using qjson, , savegame example.

hope helps.