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QSettings::beginWriteArray() produces incorrect output under Linux (bug?)

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  • JonBJ JonB

    Qt 5.12.2 as supplied with Ubuntu 19.04, at least.

    See the example code at https://doc.qt.io/qt-5/qsettings.html#beginWriteArray. Additionally I have called QSettings.setDefaultFormat(QSettings.Format.IniFormat), but I don't imagine that's relevant***.

    The sample output shown as intended is:

    The generated keys will have the form
    
        logins/size
        logins/1/userName
        logins/1/password
        logins/2/userName
        logins/2/password
        logins/3/userName
        logins/3/password
    

    However, I get that output but with \s where it should be /s, e.g. logins\1\userName :(

    We are admonished not to go for backslashes instead of forward slashes in our own keys, for good reason....

    Could someone kindly verify under Linux at least whether they get same? What about Windows? I worry about reporting this, because then if they fix it the previously-saved arrays in files may not read in? :(

    *** EDIT Hmmm... Perhaps that IniFormat is actually what the behaviour is all about? (I'm just using it at present so all platforms save to a file, not Windows registry.) But there is

    On Unix, NativeFormat and IniFormat mean the same thing

    and there is

    QSettings always treats backslash as a special character and provides no API for reading or writing such entries.

    though of course the backslashes I am seeing are in QSettings-generated key names, not my values.

    Nope: I just tried removing the IniFormat: Linux saved it as "native" .conf file instead of .ini, but they are still all backslashes.

    Still scary!?

    Pl45m4P Offline
    Pl45m4P Offline
    Pl45m4
    wrote on last edited by Pl45m4
    #2

    @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

    logins\1\userName

    How did you print this? With toString() or is this in your settings file?

    1. Do not use slashes ('/' and '\') in section or key names; the backslash character is used to separate sub keys (see below). On windows '' are converted by QSettings to '/', which makes them identical.

    (From https://doc.qt.io/qt-5/qsettings.html#section-and-key-syntax)

    Maybe its a conversion issue from QSetting together with Linux OS (I would understand, if it was the other way round)
    I can test on Win 10 (Qt 5.11.2) and Ubuntu 18.04 (Qt 5.13.2) later.

    UPDATE:

    Windows (5.11.2):

    • ini file
    • QSettings::Format::IniFormat set
    [logins]
    1\userName=userName
    1\password=password
    2\userName=userName
    2\password=password
    

    Linux (Qt 5.13.2):

    • same code / project as on Windows
    • same, unsatisfying output... :(
    [logins]
    1\password=password
    1\userName=userName
    2\password=password
    2\userName=userName
    

    If debugging is the process of removing software bugs, then programming must be the process of putting them in.

    ~E. W. Dijkstra

    JonBJ 1 Reply Last reply
    2
    • Pl45m4P Pl45m4

      @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

      logins\1\userName

      How did you print this? With toString() or is this in your settings file?

      1. Do not use slashes ('/' and '\') in section or key names; the backslash character is used to separate sub keys (see below). On windows '' are converted by QSettings to '/', which makes them identical.

      (From https://doc.qt.io/qt-5/qsettings.html#section-and-key-syntax)

      Maybe its a conversion issue from QSetting together with Linux OS (I would understand, if it was the other way round)
      I can test on Win 10 (Qt 5.11.2) and Ubuntu 18.04 (Qt 5.13.2) later.

      UPDATE:

      Windows (5.11.2):

      • ini file
      • QSettings::Format::IniFormat set
      [logins]
      1\userName=userName
      1\password=password
      2\userName=userName
      2\password=password
      

      Linux (Qt 5.13.2):

      • same code / project as on Windows
      • same, unsatisfying output... :(
      [logins]
      1\password=password
      1\userName=userName
      2\password=password
      2\userName=userName
      
      JonBJ Offline
      JonBJ Offline
      JonB
      wrote on last edited by JonB
      #3

      @Pl45m4 said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

      logins\1\userName

      How did you print this? With toString() or is this in your settings file?

      This is what ends up in the file (else I wouldn't be reporting an issue!) :)

      As per the docs and the example there I quoted, they claim it should be logins/1/userName, but it's logins\1\userName. Honest, guv!

      Do not use slashes ('/' and '') in section or key names; the backslash character is used to separate sub keys (see below). On windows '' are converted by QSettings to '/', which makes them identical.

      Yes, that's why they I said they admonish us not to use them ourselves. And I don't. In case you're not aware, this is an issue of what QSettings::beginWriteArray() is producing, not me. They are choosing to implement "save array" via multiple keys-worth of output. The docs say they will use '/', which I feel marginally safe about, but in practice at least under Ubuntu they are outputting \, which I'm less safe about :)

      This will presumably be either a big in the (intended) code, or incorrect documentation.

      Thank you, yes, please do try on whatever platform(s) you have. Armed with your results, I will presumably then have to go raise a bug report....

      EDIT I think your latest modification has just crossed with my reply. Then it looks like it's not any better/different under Windows either....

      Pl45m4P 1 Reply Last reply
      1
      • JonBJ JonB

        @Pl45m4 said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

        logins\1\userName

        How did you print this? With toString() or is this in your settings file?

        This is what ends up in the file (else I wouldn't be reporting an issue!) :)

        As per the docs and the example there I quoted, they claim it should be logins/1/userName, but it's logins\1\userName. Honest, guv!

        Do not use slashes ('/' and '') in section or key names; the backslash character is used to separate sub keys (see below). On windows '' are converted by QSettings to '/', which makes them identical.

        Yes, that's why they I said they admonish us not to use them ourselves. And I don't. In case you're not aware, this is an issue of what QSettings::beginWriteArray() is producing, not me. They are choosing to implement "save array" via multiple keys-worth of output. The docs say they will use '/', which I feel marginally safe about, but in practice at least under Ubuntu they are outputting \, which I'm less safe about :)

        This will presumably be either a big in the (intended) code, or incorrect documentation.

        Thank you, yes, please do try on whatever platform(s) you have. Armed with your results, I will presumably then have to go raise a bug report....

        EDIT I think your latest modification has just crossed with my reply. Then it looks like it's not any better/different under Windows either....

        Pl45m4P Offline
        Pl45m4P Offline
        Pl45m4
        wrote on last edited by Pl45m4
        #4

        @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

        Thank you, yes, please do try on whatever platform(s) you have. Armed with your results, I will presumably then have to go raise a bug report....

        Additionally I think there is a mistake or typo in the code example :)

        QList<Login> logins; // QList named LOGINS
        ...
        
        QSettings settings;
        settings.beginWriteArray("logins");
        for (int i = 0; i < logins.size(); ++i) {
            settings.setArrayIndex(i);
            settings.setValue("userName", list.at(i).userName); // LIST.at(i)???
            settings.setValue("password", list.at(i).password); // LIST.at(i)??? Shouldn't it be "logins.at(i)"?!
        }
        

        Discovered another weird thing, as I'm comparing the ini file on Window with the ini file on Linux.
        When you look at the order, you will see that Linux wrote password, userName, while on WIndows it's userName, password (as supposed due to code, where "userName" is written to settings first)...


        If debugging is the process of removing software bugs, then programming must be the process of putting them in.

        ~E. W. Dijkstra

        JonBJ 1 Reply Last reply
        0
        • Pl45m4P Pl45m4

          @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

          Thank you, yes, please do try on whatever platform(s) you have. Armed with your results, I will presumably then have to go raise a bug report....

          Additionally I think there is a mistake or typo in the code example :)

          QList<Login> logins; // QList named LOGINS
          ...
          
          QSettings settings;
          settings.beginWriteArray("logins");
          for (int i = 0; i < logins.size(); ++i) {
              settings.setArrayIndex(i);
              settings.setValue("userName", list.at(i).userName); // LIST.at(i)???
              settings.setValue("password", list.at(i).password); // LIST.at(i)??? Shouldn't it be "logins.at(i)"?!
          }
          

          Discovered another weird thing, as I'm comparing the ini file on Window with the ini file on Linux.
          When you look at the order, you will see that Linux wrote password, userName, while on WIndows it's userName, password (as supposed due to code, where "userName" is written to settings first)...

          JonBJ Offline
          JonBJ Offline
          JonB
          wrote on last edited by JonB
          #5

          @Pl45m4
          My code is actually in Python, it's the same as the example but I didn't copy that bit of the C++ code so I didn't notice. Yes, using list in their code example is wrong, it should be logins :)

          I wouldn't rely on the order being the same from code to file or across platforms. QSettings probably holds some unordered dictionary for the keys, so output order would not be guaranteed. And that would be reasonable for ini file/registry saving.

          The only bit I care about is whether the file ends up with forward or backward slashes!

          Pl45m4P 1 Reply Last reply
          0
          • JonBJ JonB

            @Pl45m4
            My code is actually in Python, it's the same as the example but I didn't copy that bit of the C++ code so I didn't notice. Yes, using list in their code example is wrong, it should be logins :)

            I wouldn't rely on the order being the same from code to file or across platforms. QSettings probably holds some unordered dictionary for the keys, so output order would not be guaranteed. And that would be reasonable for ini file/registry saving.

            The only bit I care about is whether the file ends up with forward or backward slashes!

            Pl45m4P Offline
            Pl45m4P Offline
            Pl45m4
            wrote on last edited by Pl45m4
            #6

            @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

            The only bit I care about is whether the file ends up with forward or backward slashes!

            The slashes in the doc could be just for demonstration purposes. Just to show the QSetting hierarchy?!

            • The generated keys will have the form

            What if "form" is meant in terms of hierarchy, separated by single slashes and not showing the actual content of the save file?!

            If this is the case, it's very misleading, but occording to QSettings doc (at least on Windows) QSettings ignores '\' and converts them to '/' anyway...

            So it could be an unfortunately worded example for this:

            - logins
            -------- 1
            ------------- userName
            ------------- password
            -------- 2
            ------------- userName
            ------------- password

            Edit:

            Looks like arrays always have backslashes (if they should? I dont know...)
            https://forum.qt.io/topic/79494/qsetting-array/4

            Just found a version of QSettings code online.
            https://github.com/radekp/qt/blob/master/src/corelib/io/qsettings.cpp

            void QSettingsPrivate::processChild(QString key, ChildSpec spec, QMap<QString, QString> &result)
            {
                if (spec != AllKeys) {
                    int slashPos = key.indexOf(QLatin1Char('/')); // ### SLASH
                    if (slashPos == -1) {
                        if (spec != ChildKeys)
                            return;
                    } else {
                        if (spec != ChildGroups)
                            return;
                        key.truncate(slashPos);
                    }
                }
                result.insert(key, QString());
            }
            
            void QSettingsPrivate::beginGroupOrArray(const QSettingsGroup &group)
            {
                groupStack.push(group);
                if (!group.name().isEmpty()) {
                    groupPrefix += group.name();
                    groupPrefix += QLatin1Char('/'); // # SLASH!!
                }
            }
            

            In addition to that, QSettings uses the QDir::separator() which indeed returns a single slash ('/') on my Linux system and a backslash on Windows....

            I really don't know where the backslash is coming from and WHY? :-)


            If debugging is the process of removing software bugs, then programming must be the process of putting them in.

            ~E. W. Dijkstra

            JonBJ 1 Reply Last reply
            1
            • Pl45m4P Pl45m4

              @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

              The only bit I care about is whether the file ends up with forward or backward slashes!

              The slashes in the doc could be just for demonstration purposes. Just to show the QSetting hierarchy?!

              • The generated keys will have the form

              What if "form" is meant in terms of hierarchy, separated by single slashes and not showing the actual content of the save file?!

              If this is the case, it's very misleading, but occording to QSettings doc (at least on Windows) QSettings ignores '\' and converts them to '/' anyway...

              So it could be an unfortunately worded example for this:

              - logins
              -------- 1
              ------------- userName
              ------------- password
              -------- 2
              ------------- userName
              ------------- password

              Edit:

              Looks like arrays always have backslashes (if they should? I dont know...)
              https://forum.qt.io/topic/79494/qsetting-array/4

              Just found a version of QSettings code online.
              https://github.com/radekp/qt/blob/master/src/corelib/io/qsettings.cpp

              void QSettingsPrivate::processChild(QString key, ChildSpec spec, QMap<QString, QString> &result)
              {
                  if (spec != AllKeys) {
                      int slashPos = key.indexOf(QLatin1Char('/')); // ### SLASH
                      if (slashPos == -1) {
                          if (spec != ChildKeys)
                              return;
                      } else {
                          if (spec != ChildGroups)
                              return;
                          key.truncate(slashPos);
                      }
                  }
                  result.insert(key, QString());
              }
              
              void QSettingsPrivate::beginGroupOrArray(const QSettingsGroup &group)
              {
                  groupStack.push(group);
                  if (!group.name().isEmpty()) {
                      groupPrefix += group.name();
                      groupPrefix += QLatin1Char('/'); // # SLASH!!
                  }
              }
              

              In addition to that, QSettings uses the QDir::separator() which indeed returns a single slash ('/') on my Linux system and a backslash on Windows....

              I really don't know where the backslash is coming from and WHY? :-)

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by JonB
              #7

              @Pl45m4
              From your https://forum.qt.io/topic/79494/qsetting-array/4 it looks like it is producing \s elsewhere. At least I know. Then it's perhaps just a docs issue.

              Pl45m4P 1 Reply Last reply
              0
              • JonBJ JonB

                @Pl45m4
                From your https://forum.qt.io/topic/79494/qsetting-array/4 it looks like it is producing \s elsewhere. At least I know. Then it's perhaps just a docs issue.

                Pl45m4P Offline
                Pl45m4P Offline
                Pl45m4
                wrote on last edited by Pl45m4
                #8

                @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

                @Pl45m4
                From your https://forum.qt.io/topic/79494/qsetting-array/4 it looks like it is producing \s elsewhere.

                Just because others face the same issue or behavior, it doesn't mean that it's intended or correct :)
                Could be wrong (buggy) since years / many releases, but seems to work :)

                @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

                Then it's perhaps just a docs issue.

                The second part of my post (the Qt source code) shows that it's not a doc issue. You can also find the same comment in the source code ("The generated keys will have the form.... bla...")... Really weird...


                If debugging is the process of removing software bugs, then programming must be the process of putting them in.

                ~E. W. Dijkstra

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                • Christian EhrlicherC Offline
                  Christian EhrlicherC Offline
                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on last edited by
                  #9

                  What's the problem as long as beginReadArray() can read them later on?

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                  • Christian EhrlicherC Christian Ehrlicher

                    What's the problem as long as beginReadArray() can read them later on?

                    JonBJ Offline
                    JonBJ Offline
                    JonB
                    wrote on last edited by JonB
                    #10

                    @Christian-Ehrlicher
                    At the time I raised the question I did not yet know whether it could be read OK. Now I am pleased to report it does. I merely asked to see if it was the same for others. I do not know if there any other consequences, hopefully not.

                    So you belong to the "it doesn't matter what the docs say as long as it works" school ;-)

                    Pl45m4P Christian EhrlicherC 2 Replies Last reply
                    0
                    • JonBJ JonB

                      @Christian-Ehrlicher
                      At the time I raised the question I did not yet know whether it could be read OK. Now I am pleased to report it does. I merely asked to see if it was the same for others. I do not know if there any other consequences, hopefully not.

                      So you belong to the "it doesn't matter what the docs say as long as it works" school ;-)

                      Pl45m4P Offline
                      Pl45m4P Offline
                      Pl45m4
                      wrote on last edited by Pl45m4
                      #11

                      myCodeWorks.jpg

                      Nevertheless, it would be satisfying (for me as well) if someone could explain where the backslashes come from, because even in current sources arrays start explicitly with '/'. (https://github.com/radekp/qt/blob/master/src/corelib/io/qsettings.cpp#L393)


                      If debugging is the process of removing software bugs, then programming must be the process of putting them in.

                      ~E. W. Dijkstra

                      JonBJ 1 Reply Last reply
                      2
                      • Pl45m4P Pl45m4

                        myCodeWorks.jpg

                        Nevertheless, it would be satisfying (for me as well) if someone could explain where the backslashes come from, because even in current sources arrays start explicitly with '/'. (https://github.com/radekp/qt/blob/master/src/corelib/io/qsettings.cpp#L393)

                        JonBJ Offline
                        JonBJ Offline
                        JonB
                        wrote on last edited by JonB
                        #12

                        @Pl45m4

                        Nevertheless, it would be satisfying (for me as well) if someone could explain where the backslashes come from

                        All backslashes live in a land of their own, where everything is the wrong way round. They emanate from there, mystically. And sometimes arrive in pairs.

                        I will raise a report on the Qt bug forum tomorrow and they can decide whether it's a documentation or behaviour issue.

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                        • JonBJ JonB

                          @Christian-Ehrlicher
                          At the time I raised the question I did not yet know whether it could be read OK. Now I am pleased to report it does. I merely asked to see if it was the same for others. I do not know if there any other consequences, hopefully not.

                          So you belong to the "it doesn't matter what the docs say as long as it works" school ;-)

                          Christian EhrlicherC Offline
                          Christian EhrlicherC Offline
                          Christian Ehrlicher
                          Lifetime Qt Champion
                          wrote on last edited by
                          #13

                          @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

                          So you belong to the "it doesn't matter what the docs say as long as it works" school ;-)

                          No, but to the 'I don't care about the internals as long as the library can read it again'. Or do you really care how e.g. QDataStream encodes and decodes the stuff as long as it is doing what you expect?

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                          • Christian EhrlicherC Christian Ehrlicher

                            @JonB said in QSettings::beginWriteArray() produces incorrect output under Linux (bug?):

                            So you belong to the "it doesn't matter what the docs say as long as it works" school ;-)

                            No, but to the 'I don't care about the internals as long as the library can read it again'. Or do you really care how e.g. QDataStream encodes and decodes the stuff as long as it is doing what you expect?

                            JonBJ Offline
                            JonBJ Offline
                            JonB
                            wrote on last edited by JonB
                            #14

                            @Christian-Ehrlicher
                            So are you saying you'd rather I didn't report it? When the docs choose to tell me the file will look like such & such and I try it and it does not, I shouldn't question it, shouldn't ask about it here but just assume it's fine? I don't understand your point/suggestion?

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                            • Christian EhrlicherC Offline
                              Christian EhrlicherC Offline
                              Christian Ehrlicher
                              Lifetime Qt Champion
                              wrote on last edited by
                              #15

                              From my pov that's only a documentation error.

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                              • Christian EhrlicherC Christian Ehrlicher

                                From my pov that's only a documentation error.

                                JonBJ Offline
                                JonBJ Offline
                                JonB
                                wrote on last edited by JonB
                                #16

                                @Christian-Ehrlicher
                                No problem. I'll log it tomorrow, if it's only docs and the behaviour is intended then at least someone (might be you!) will have seen it and can decide.

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                                • JonBJ Offline
                                  JonBJ Offline
                                  JonB
                                  wrote on last edited by
                                  #17

                                  For right or for wrong, raised https://bugreports.qt.io/browse/QTBUG-81951. Hopefully someone will check whether it's only a documentation issue or if it has any consequences.

                                  1 Reply Last reply
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