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Qt 5.5 - QList variable causes compilation to fail

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  • K Offline
    K Offline
    knight556
    wrote on last edited by
    #1

    Hi guys, I'm trying to include a QList member variable in my class, e.g.

    QList<QString> m_myList;

    I have included all the relevant classes, ie. <QList>, <QString>, etc, and I have QT += core in my make file, but the compilation always fails with the message:

    expected member name or ';' after declaration specifiers
    QList<QString> m_myList;
    –––––^

    I have tried everything I can think of to get it to work. I feel like I'm making a very fundamental mistake somewhere! Any ideas?

    1 Reply Last reply
    0
    • dheerendraD Offline
      dheerendraD Offline
      dheerendra
      Qt Champions 2022
      wrote on last edited by
      #2

      Your error may be coming line previous to this line. Just check. I don't see any issue with above line of code.

      Dheerendra
      @Community Service
      Certified Qt Specialist
      http://www.pthinks.com

      1 Reply Last reply
      4
      • K Offline
        K Offline
        knight556
        wrote on last edited by
        #3

        I wish it was that easy, but if that line is commented out, the rest of the program runs perfectly.

        mrjjM 1 Reply Last reply
        0
        • K knight556

          I wish it was that easy, but if that line is commented out, the rest of the program runs perfectly.

          mrjjM Offline
          mrjjM Offline
          mrjj
          Lifetime Qt Champion
          wrote on last edited by
          #4

          @knight556 said:

          And the
          #include <QList>
          #include <QString>

          are in the .H file ?

          with the class having the m_mylist?

          Are you using Creator and a pro file or how do you build the project ?

          1 Reply Last reply
          1
          • K Offline
            K Offline
            knight556
            wrote on last edited by
            #5

            The includes are in the .cpp file, and yes I'm using Creator with a pro file. I've noticed that if I declare a QList within a class method then it compiles just fine, it's only when I try and declare it as a member variable that it complains.

            mrjjM 1 Reply Last reply
            0
            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #6

              Hi and welcome to devnet,

              Not a direct answer but since you want a QList of QString, why not use QStringList ?

              Interested in AI ? www.idiap.ch
              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

              1 Reply Last reply
              1
              • K knight556

                The includes are in the .cpp file, and yes I'm using Creator with a pro file. I've noticed that if I declare a QList within a class method then it compiles just fine, it's only when I try and declare it as a member variable that it complains.

                mrjjM Offline
                mrjjM Offline
                mrjj
                Lifetime Qt Champion
                wrote on last edited by
                #7

                @knight556
                Hi

                But if you declare m_list in the H file you must have
                #include <QList>
                #include <QString>

                in the H file (and not cpp file ) or the type is unknown :)
                Its not enough to include in CPP file.

                I have noticed that if I declare a QList within a class method ...

                Yes as you included the files in the cpp I guess.

                K 1 Reply Last reply
                1
                • K Offline
                  K Offline
                  knight556
                  wrote on last edited by
                  #8
                  This post is deleted!
                  1 Reply Last reply
                  0
                  • mrjjM mrjj

                    @knight556
                    Hi

                    But if you declare m_list in the H file you must have
                    #include <QList>
                    #include <QString>

                    in the H file (and not cpp file ) or the type is unknown :)
                    Its not enough to include in CPP file.

                    I have noticed that if I declare a QList within a class method ...

                    Yes as you included the files in the cpp I guess.

                    K Offline
                    K Offline
                    knight556
                    wrote on last edited by
                    #9

                    @mrjj Moving the includes to the .h file didn't help.

                    @SGaist Yes the QStringList does in fact work, but what I have failed to mention (for simplicity) is that this bug is occurring for all data types, eg. QList<int> fails as well. As it turns out I want to use my own custom class as the list type, but I can't hope to get that working until I get the QList working with more basic data types first!

                    Creator is clearly happy with QList being used, because if I start typing on the next line something like:
                    m_mylist.
                    the autocomplete/intellisense/whatever-it's-called will give me the option of append(), so something is working correctly!

                    mrjjM 1 Reply Last reply
                    0
                    • K knight556

                      @mrjj Moving the includes to the .h file didn't help.

                      @SGaist Yes the QStringList does in fact work, but what I have failed to mention (for simplicity) is that this bug is occurring for all data types, eg. QList<int> fails as well. As it turns out I want to use my own custom class as the list type, but I can't hope to get that working until I get the QList working with more basic data types first!

                      Creator is clearly happy with QList being used, because if I start typing on the next line something like:
                      m_mylist.
                      the autocomplete/intellisense/whatever-it's-called will give me the option of append(), so something is working correctly!

                      mrjjM Offline
                      mrjjM Offline
                      mrjj
                      Lifetime Qt Champion
                      wrote on last edited by
                      #10

                      @knight556

                      Oh ok. sorry for assuming it was that basic thing,

                      Can we try a simple test just to be sure compiler not funky?

                      If you create a new console project and then
                      right click -> add new -> Header file and call it thehappylist.h
                      and put code below in thehappylist.h

                      #ifndef THEHAPPYLIST
                      #define THEHAPPYLIST
                      
                      #include <QList>
                      #include <QString>
                      class Happy {
                      public:
                          QList<QString> m_list;
                      };
                      #endif // THEHAPPYLIST
                      

                      and then the main.cpp

                      #include "thehappylist.h"
                      int main(int argc, char *argv[])
                      {
                          Happy h;
                          h.m_list.append("test");
                      }
                      

                      And tell me if that compiles ?

                      1 Reply Last reply
                      1
                      • K Offline
                        K Offline
                        knight556
                        wrote on last edited by
                        #11

                        @mrjj said:

                        #include "thehappylist.h"
                        int main(int argc, char *argv[])
                        {
                        Happy h;
                        h.m_list.append("test");
                        }

                        Hi, yes it does compile... which is frustrating because that doesn't help find the problem.

                        1 Reply Last reply
                        0
                        • mrjjM Offline
                          mrjjM Offline
                          mrjj
                          Lifetime Qt Champion
                          wrote on last edited by
                          #12

                          HI

                          Well, its not an include path thing then.
                          Since the mini sample works.

                          Would it be possible to post your code ?
                          I really can not get a clue of what could be wrong as you have the includes
                          and it all sounds ok.

                          1 Reply Last reply
                          1
                          • K Offline
                            K Offline
                            knight556
                            wrote on last edited by
                            #13

                            I'm working on quite a large project (it's basically a DICOM image viewer), but I will attempt to create a minimal working example.

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                            0
                            • K Offline
                              K Offline
                              knight556
                              wrote on last edited by
                              #14

                              OK now this is weird. I'm not sure how I came to this, but instead of writing:

                              QList<QString> m_mylist;

                              I write:

                              ::QList<QString> m_mylist

                              It compiles and works... however Qt Creator doesn't seem to like it as the terms QList and QString are not coloured purple as normal.
                              Any ideas why this works?

                              JKSHJ 1 Reply Last reply
                              0
                              • K knight556

                                OK now this is weird. I'm not sure how I came to this, but instead of writing:

                                QList<QString> m_mylist;

                                I write:

                                ::QList<QString> m_mylist

                                It compiles and works... however Qt Creator doesn't seem to like it as the terms QList and QString are not coloured purple as normal.
                                Any ideas why this works?

                                JKSHJ Offline
                                JKSHJ Offline
                                JKSH
                                Moderators
                                wrote on last edited by
                                #15

                                @knight556 said:

                                OK now this is weird. I'm not sure how I came to this, but instead of writing:

                                QList<QString> m_mylist;

                                I write:

                                ::QList<QString> m_mylist

                                It compiles and works... however Qt Creator doesn't seem to like it as the terms QList and QString are not coloured purple as normal.
                                Any ideas why this works?

                                1. Did you redefine "QList" somewhere else in your code?
                                2. Does this only happen in this particular class, or does it also happen if you add a QList member to other classses?

                                Qt Doc Search for browsers: forum.qt.io/topic/35616/web-browser-extension-for-improved-doc-searches

                                1 Reply Last reply
                                1
                                • K Offline
                                  K Offline
                                  knight556
                                  wrote on last edited by
                                  #16

                                  Well that got me thinking, so I had a look and for some reason in another one of my classes I had listed a forward reference to QList. I have now deleted that line of code and the rest of the program compiles and works as expected, without needing the extra :: bits at the start of the QList declaration!
                                  So... clearly I don't understand forward references. Thanks for the help everyone!

                                  1 Reply Last reply
                                  0
                                  • SGaistS Offline
                                    SGaistS Offline
                                    SGaist
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #17

                                    It's pretty unusual to forward declare QList, why did you do that in the first place ?

                                    Interested in AI ? www.idiap.ch
                                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                    1 Reply Last reply
                                    1
                                    • K Offline
                                      K Offline
                                      knight556
                                      wrote on last edited by
                                      #18

                                      I was learning Qt through a series of Pluralsight videos and the instructor was basically forward declaring every class he was gonna use, so I got into that habit. Time to go back and remove some of that rubbish.

                                      1 Reply Last reply
                                      0
                                      • SGaistS Offline
                                        SGaistS Offline
                                        SGaist
                                        Lifetime Qt Champion
                                        wrote on last edited by
                                        #19

                                        Even QString ?

                                        Interested in AI ? www.idiap.ch
                                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                                        1 Reply Last reply
                                        1
                                        • K Offline
                                          K Offline
                                          knight556
                                          wrote on last edited by
                                          #20

                                          Yep even QString. Is forward referencing even necessary if you put all your includes in the header file? I always thought forward referencing was only needed if you had 2 classes that referenced one another, but of course 1 had to be defined before the other.

                                          JKSHJ 1 Reply Last reply
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