Using QSettings on Mac crashes on launch. Is there a fix?

sandy.martel23

You are using QSettings in a global variable. Move the initialisation inside the main().

Looks like you are using a statically linked Qt, right ? Your QSettings is a global variable, QSettings implementation itself rely on other global variables. The order of initialisation of global variables is undefined.
What could work, from worst to best:

shuffle the link order around to get QSettings globals initialised first (that would be a very fragile fix)
link Qt as a shared library, shared lib would be loaded and initialised before your code.
Don't build a QSettings as a global, replace it with a QSettings * and build it in main().

Crossy

@SGaist Hello. Thanks for your response. I'm just recompiling Qt now with the patch from the gerrit submission. If it does work, I will link a minimal example in the bug report that will reproduce the initial error. Is that the best way to do it?

Crossy

@sandy.martel23 Thanks for your response. I'm going to see if the patch in the bug report fixes the error. If not this will be what I try next :) Just a quick question about it though (if that's ok) :)

At the moment I've got globalsettings.cpp. In there is where I have 'QSettings settings' and then I refer to this object in some static functions which are in globalsettings.cpp. Example below:

// globalsettings.cpp
#include <QSettings>
#include "globalsettings.h"

// Initialise some variables from globalsettings.h.

QSettings settings;

void GlobalSettings::saveSetting(int day) // This function is defined statically in globalsettings.h.
{
    settings.setValue("dayNumber", day);
}

In main.cpp I define the information needed for QCoreApplication which is why I haven't included app name etc as parameters in the QSettings object.

So my question, is, where should I move the initialisation of the QSettings object, as unless I've misunderstood (possible because I'm a newbie), I can't have a main loop in globalsettings.cpp, and if I put it in the main loop in main.cpp, it won't be accessible. As I said, I may have totally misunderstood but would appreciate any clarification :)

SGaist

You don't need a global QSettings. Just create one when you need to either read or write a setting and be done with it.

Crossy

@SGaist Thanks. I assume this means that the bug report was not related to my problem? Thanks for your help!

SGaist

The bug report was about a corrupted file which doesn't match your use case.

All in all, since you have already built Qt with the patch applied, did you also test it for your use case ?

Crossy

@SGaist Qt with the patch applied is still building ;( I tested the above with the original build I was using when I got the error and the program loaded with no problems. Thanks again for your help :)

SGaist

Still building ? What machine do you have ? What options did you pass to configure ?

Crossy

@SGaist A 2011 Mac book pro. The reason it's still building because it failed about an hour in while I was out. So I'm building it again :)

SGaist

If you only need the core modules for your application, just build qtbase, that will save you lots of times

Crossy

@SGaist Thanks - not sure if i did that or not, lol, but I'll do it next time as I'm only using the core modules :)

sandy.martel23

@Crossy said:

QSettings settings;

void GlobalSettings::saveSetting(int day) // This function is defined statically in globalsettings.h.
{
settings.setValue("dayNumber", day);
}

SGaist is right, the code should look like this:

void GlobalSettings::saveSetting(int day) // This function is defined statically in globalsettings.h.
{
QSettings settings; // <-- NOT a global
settings.setValue("dayNumber", day);
}

This is much better than your current implementation, since the destructor of QSettings will save/sync the preferences right away.
And if the global is really what is causing the problem, that would fix it.

Crossy

@sandy.martel23 Thanks for your help :) It was the global causing the problem - after changing it to how you and SGaist suggested, it has worked :) Thank you!

SGaist

Good !

Since everything is working now, please mark the thread as solved using the "Topic Tool" button so that other forum users may know a solution has been found :)