Qt6 topics merged with General

set<int> in Qt creator and debugger

  • Yesterday I came across a strange output making no sense at all. Today I could replicate very easily.

    This is on windows 10, Qt creator 4.2.1 and

    Am I missing something?

  • Showing that it has something to do with the debugger

  • Lifetime Qt Champion

    well i started on Qt5.5 and back then,
    when upgrading my my beloved win 7 to win 10, i also saw
    some strange issues and warnings. In Qt/Creator.

    Could you post code. ?

    Yes its easy to re-type but im old fashioned and likes that the code really IS the same. :)

    Just wondering if gone in later versions/gdb version.

    It looks like a bug to me. so lets test some more?

  • @mrjj


    #include <set>
    #include <QDebug>
    int main(int argc, char *argv[])
        std::set < int > setint;
        for ( unsigned i = 0; i < 20; ++i )
            setint.insert (i);
        for ( std::set<int>::const_iterator it = setint.begin(); it != setint.end(); ++it)
            qDebug() << *it;
        return 0;

    and here the .pro file, which holds another surprise with new creator.

    QT += core
    QT -= gui
    CONFIG += c++11
    TARGET = TestDebugSet
    CONFIG += console
    CONFIG -= app_bundle
    TEMPLATE = app
    SOURCES += main.cpp
    # The following define makes your compiler emit warnings if you use
    # any feature of Qt which as been marked deprecated (the exact warnings
    # depend on your compiler). Please consult the documentation of the
    # deprecated API in order to know how to port your code away from it.
    # You can also make your code fail to compile if you use deprecated APIs.
    # In order to do so, uncomment the following line.
    # You can also select to disable deprecated APIs only up to a certain version of Qt.
    #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

    Certainly it is good to do more testing. I did not expect that it is as easily reproducable.
    If you mean old-fashioned -> lazy , I'm old-fashioned too. ;)

  • I see the same with Qt 5.7.1 and MinGW 5.3.0.

    Wasn't there something to be installed alongside with the tools for debugging with gdb?

    [edit, koahnig] That is what I remembered. Found in here
    GDB On Windows, use the Python-enabled GDB versions that is bundled with the Qt package or comes with recent versions of MinGW. On most Linux distributions the GDB builds shipped with the system are sufficient. You can also build your own. Follow the instructions in Building GDB. Builds of GDB shipped with Xcode on macOS are no longer supported.

  • Moderators

    We (at least I) can't see the pictures.

  • @kshegunov

    Here is a link to the second picture. Part of the picture is the first picture anyway.

  • Moderators

    I'd venture to say you're seeing the buckets for the values, not the actual values. What does the code output to the debug stream? Is it the numbers shuffled up?

  • @kshegunov
    The output to qDebug() is correct. You should see, it is part of the lower end of the picture.

    What do you mean with buckets?
    Whatever this would be, shouldn't it non-repeating?

  • Moderators

    @koahnig said in set<int> in Qt creator and debugger:

    What do you mean with buckets?
    Whatever this would be, shouldn't it non-repeating?

    No, it can be repeating, it depends on the internal structure of std::set. I assumed (erroneously) the set is implemented as a hash-table (like in Qt), so that's where "buckets" come from - it's the index of the array where the actual data is kept. Anyway, after a quick lookup I see it's a red-black tree (i.e. like QMap), so my new hypothesis is you're looking at the node index be it left node or right. I'd even make a further step and speculate 0 is the root node, 1 is the left node and 2 is the right node (relative to the parent).

    In any case you should probably file a bug report on it, as the debug helpers don't seem to properly resolve the actual data.

  • @kshegunov

    Bug report filed QTCREATORBUG-17653

  • Lifetime Qt Champion


    "If you mean old-fashioned -> lazy , I'm old-fashioned too. ;)"
    Yes also that :))

    Tried at home with Qt5.7, Creator 4.1.0, win 10, mingw, gdb 7.10.1

    alt text

  • @mrjj

    Thanks for checking.

    This reflects my memory. I had upgraded recently to latest qt creator version, but left all the different Qt lib version and their associated tools, respectively there might be an update somewhere, but not on all different Qt lib versions.

    I am pretty sure that the display worked prior to the upgrade of creator.

    Unfortunately, I cannot go back easily to previous Qt creator setup for checking. At least I will not dare to do, because there have been adaptations to project setups.

  • @mrjj

    Took the liberty to add a comment and your screenshot to the bug report on JIRA.

  • Lifetime Qt Champion

    Super. So we are thinking its related to Creator version and not so much Qt version?
    Sounds like. Was working in Creator 3.6 ? and then upgraded to 4.2.1 and
    it was now incorrect?

  • @mrjj
    Not sure, but I think I had a 4.1.x already bnefore upgrading. This would correlate with your findings.
    [edit:koahnig] Yes, the change to V4.2.1 brought up the problem.

    I am too "old-fashioned" to keep track of this.
    In general I am a slow upgrader, because "Never change a running system". Therefore, I am mainly using 5.4.2 at the moment. This gives the nasty message when starting up the application on win10, but it works and that is the point.

  • Lifetime Qt Champion

    So if I upgrade my Creator, i should get the same. maybe.
    You just download other Creator from
    and run it ?

  • @mrjj
    No, I simply used the maintenance tool and used the second entry (updating/upgrading?).
    Therefore, there could be also some updates invloved for the other tools. I did not pay attention, but it is probably save to assume that the installation for Qt5.4.2 stayed as it was.

  • Lifetime Qt Champion

    Hi i used the update option and updated ONLY Creator.
    ( and some docs that was not de-selectable)

    And i have issue now
    alt text

    So it seems a bug in 4.2.1 .

    Soo where is my downgrade option ? :)

  • @mrjj

    Bad luck, I guess. ;)

    At least I know that this is not an issue with my specific machine.

    Somehow it would be good to have parallel installations of Qt creator as well. However, the implications might be huge.

  • Lifetime Qt Champion

    Its really reproducible.
    Just tried in virtual. Same result.

    In theory , there should be nothing stopping us from having multiple Creators but
    i wonder if a 3.6 version can load the plugins of 4.2.1

  • @mrjj

    I doubt that creator 3.6 can load plugins of version 4.2.1.

    I had wasted a while ago my time with enhancing the doxygen plugin. My rational was that at least I can use while doing a complete compilation of creator with all plugins. However, I had found out that another plugin, which I was relying on, changed interface. Adding the mostly non-existing documentation for feaures and interfaces completes in my opinion the nightmare.

    Do you know if you can use plugins the other way around (e.g. 3.6 plugins in 4.2)?
    Respectively, can you mix MinGW plugins with VS plugins?
    The latter one is probably killed by incompatibility of different compilers, or is that assumption wrong?

  • Lifetime Qt Champion

    yes i assume only minor version will work.
    I have 2 creators installed currently. seems to work.
    Im not sure how compatible the plugins are but going to try an older creator:)

    We cannot use mingw plugins unless creator is compiled with mingw. I made such version to make
    testing Designer plugins easier. but to run in the normal creator it must be compiled with vs 2013 or 2015 for 5.8

  • I am wondering if this has something to do with the debugging problems?

    I am pretty sure that the settings where ok prior to creator update.

    Also this looks strange

  • Lifetime Qt Champion

    Image upload is broken :)

  • @mrjj

    Here are the links first pciture
    Second picture
    Is my handling wrong or is it a general issue with the upload?

  • Lifetime Qt Champion

    Its general issue. The image is in fact uploaded to cloud server but sadly that area is only
    available to the users on that Host. So it remains visible for some time to the poster and "some"
    and then its gone.

  • @mrjj

    If I undertand you correctly I would need to install a previous version of Qt creator separately through creator install.exe. Are you aware of any downsides when you are downgrading from the buggy version?
    E.g. are there conflicts through the various files holding settings?

    As noted before, I am not really happy to downgrade of potential version conflicts, but as it looks to me, it might be the best alternative. I need to debug structures based on std::map now. The same problem there. Probably not surprising I guess.

  • Moderators

    @koahnig said in set<int> in Qt creator and debugger:

    E.g. are there conflicts through the various files holding settings?

    There might be, you will probably at least need to reconfigure the project's kits (i.e. deleting the *.pro.user files). I'd try to load them directly first though, it might work fine.

    @koahnig said in set<int> in Qt creator and debugger:

    The same problem there.

    It's the same data structure, so no surprise at all, indeed.