C++ Gurus

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  Unsolved C++ - Can't access function in another class
  • mad-hatter

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  Solved C++ % " ?
  • JonB

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  They didn't overload operator , so everything is under control :)

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  Unsolved QSharedDataPointer detach too much ( don't call const )
  • miskol

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  @miskol It outputs 2 times "bbb". Why do you think there is a detach in your example?

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  Unsolved how to write PID control algorithm to control temperature
  • _bhum

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  @_bhum said in how to write PID control algorithm to control temperature:

  how i execute my program on raspi terminal????

  do you know how to run a program in a Linux terminal?

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  Unsolved How to use QTimer connect without Object and without slot
  • mrudula

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  Hi,
  You can use QTimer with lamda functions like this.

  connect(pTimerValidateScheduleTimeoutr, &QTimer::timeout, []() { ValidateScheduleEvent(); });
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  Unsolved Is this intentional?
  • digital_light

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  @digital_light said in Is this intentional?:

  Why are we defining Ui::LoadScreen and ::LoadScreen? Doesn't that defeat the purpose of the namespace?

  They are 2 separate classes.

  ::LoadScreen is your "actual" class where you write your code Ui::LoadScreen is a fully auto-generated class that's embedded inside ::LoadScreen.
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  Unsolved print function char FirstDriveFromMask( ULONG unitmask ) with qDebug()
  • filipdns

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  Hi,

  Not a direct answer but did you consider KDE’s Solid framework for that ?

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  Unsolved Letting the User set the respective directory within a qt wigdet application
  • Pippapo

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  @Pippapo said in Letting the User set the respective directory within a qt wigdet application:

  QString directory = fi.filePath(); QDir dir(directory); dir.setCurrent(directory);

  http://doc.qt.io/qt-5/qfileinfo.html#filePath does not return a directory, it returns the full path to the file, directory plus filename, from the docs? You should check the return result from your http://doc.qt.io/qt-5/qdir.html#setCurrent, I imagine it's returning false? Try using something more like http://doc.qt.io/qt-5/qfileinfo.html#absoluteDir ?

  P.S. At least while you're new, if you've got a function like http://doc.qt.io/qt-5/qdir.html#setCurrent which returns a result always check that! And use something like qDebug() << ... to check things as you go along, e.g.

  QString directory = fi.filePath(); qDebug() << directory;

  might have helped you.

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  Unsolved Cgal Computational Geometry algorithms integration with QT
  • ujur007

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  @ujur007

  Why should you?

  The example names are just for explanation of how to integrate a third party library. The 3rd party library is integrated through relative path within your actual project. However, you may place the 3rd party stuff anywhere and your PC.

  Basically you have to download and install the 3rd party library independent of Qt. You need to know the path to the includes and add this as relative or absolute path to INCLUDEPATH

  You have to ensure that the libraries are compiled correctly for Qt installation (32 vs 64 bit, compiler andsome stuff). You need to locate the required libraries and setup absolute or relative path and libraries in LIBS

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  Solved What parentheses at the beginning mean?
  • Engelard

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  @Engelard

  It is a C-style cast to an unspecified long pointer. When some more is around in the line you are casting to your needs.

  As you show it above you get rid of compile warnings.

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  Solved Logical public variable in object programming
  • elicat

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  @elicat said in Logical public variable in object programming:

  it is clear that * pA is a pointer to a new class A instance
  what type of object is * pA ??
  is an instance of the class but how do I declare it?

  You already answered for yourself what type of object pA is --- it's a pointer to a class instance.

  How to declare it? I gave you:

  # Outside world goes: classA *pA = new classA("Hello world");

  but if I have set this variable in a program phase and then I will have to read it later in other classes and at other times of the process .. . how can I do? Do I have to carry the variable with me at every step?

  Yes, like any other variable, if you need to access the object all over the place you have to pass it around. If it turns out(?) you often access the classA instance from your classB instance, you could create a classA * member variable in your classB and then if you're passing a classB instance around it will carry with it a classA * to save you having to pass that around separately.

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  Unsolved Why does const auto& lead to empty lists?
  • Asperamanca

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  @Asperamanca said in Why does const auto& lead to empty lists?:

  So you never do stuff like this?

  for(const auto& item : container) { // Do stuff }

  I do, I do.

  I just I think of this like I do with function parameters, but I think of function parameters differently from local variables inside a function block (like const auto& list = ...;). Once I remember they're basically the same, it now makes sense.

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  Solved Best design for code used in many classes
  • Weichao Wang

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  @Gojir4
  Many thanks!

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  Solved Constructor of a derived class
  • Weichao Wang

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  @SGaist
  Many thanks!

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  Solved abstract class
  • Weichao Wang

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  @jsulm
  Thank you! I'm going to use this mothode. The code would be a little extensive and I want to avoid the situation that it turns out to be not workable.

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  This topic is deleted!
  • DoubleC122

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  Solved abstract class and virtual function
  • Weichao Wang

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  Hi,

  With C++11, you can add the override keyword after the declaration of each function you re-implement. This will give the compiler a hint that will allow him to scream at you if you try to re-implement a non virtual function.

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  Solved Whats wrong with TCHAR?
  • Engelard

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  @kshegunov Yep, that would be fine.

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  Unsolved How to "find" all memory which program uses?
  • Engelard

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  Last report from me:
  It's working if i'll use simplest scan with for loop simply scanning every memory address from the beginning. To find variable address of my test program tooks about 24 seconds, considering that fact that that address was placed at the beginning(11 million position), and CPD with 4Ghc speed.

  I calculated, using such "simple" scan might take 2 and half hours...

  P.S. And CheatEngine doing such scan like in one second, but it was written on python, i dont know why he choose to write in that language, but must be some reason.

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  Unsolved Using a proxy for certain URL calls made by app
  • JrDeskJockey

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  @Pablo-J.-Rogina Sure will do.

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  Solved How to share Serial port opened in Main Window class with Dialog box class
  • saurabh162

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  @saurabh162 And this is the third same question: https://forum.qt.io/topic/93202/how-to-share-serial-port-opened-in-main-window-class-with-dialog-box-class

  Stop doing that!

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  Solved Mariadb query returns empty strings
  • Gosport_gaz

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  Thanks JonB, It seems that connClose() is the problem. Or more specifically the line 'mydb.removeDatabase(QSqlDatabase::defaultConnection);'. It seems that this only affects the server/client database (as I've tried it with PostresSql with the same results.)
  I'm not sure why this doesn't affect Sqlite.

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  Unsolved How do I safely call methods from another object?
  • JohnFrom

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  @J.Hilk

  connect((QObject*)sender, SIGNAL(newNodeAdded()), this, SLOT(onRefreshnodeClicked()));

  "sender not decleared in the scope"

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  This topic is deleted!
  • VRonin

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  This topic is deleted!
  • JohnFrom

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  Unsolved QTimer setInterval integer value
  • K-Str

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  hi @K-Str,

  i gave you three points to check, have done this?

  you will need to debug this issue yourself, we cannot do it for you.

  regards

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  Unsolved This seems redundant to me? Delete each single value of a map and then
  • JohnFrom

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  Hi,

  Or use qDeleteAll and then clear your container.

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  Unsolved Adding a sqlite3 header
  • Satvik

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  Hi and welcome to devnet,

  It's described here in the Qt Creator documentation.

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  Unsolved Template class creating object
  • jcga

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  I want this class to store only pointers to objects of class Obj

  Add, inside the class
  static_assert(std::is_pointer<T>::value && std::is_base_of<Obj, std::remove_pointer<T>::type>::value,"T must be a pointer to an Obj");

  Is there a way to create an object that is a pointer to an object of class T?

  T obj = new std::remove_pointer<T>::type;

  You should also have a think about what happens if the user const-qualifies T. For example, in case of ObjListP<const Obj*> mylist;

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  Solved try-finally statement behaviour in MSVC C++
  • JonB

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  @JonB said in try-finally statement behaviour in MSVC C++:

  I would not have guessed that!!!

  Yep, it's rather rarely used by the compilers at least from my observations. The usual thing you'd see is just: ret, which is the same as ret 0.

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  Solved Copying a const complex data type
  const copy appending • • devDawg

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  @devDawg said in Copying a const complex data type:

  would the best plan be to declare that data source as a C++ class

  I would think so, yes

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  Solved Strong typing problem
  • ofmrew

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  @JonB said in Strong typing problem:

  Yeah, but you don't actually have an interface keyword :)

  Nope, we don't. But that's only because we like to write more with less typing ... efficiency you see ... ;)

  It isn't. It's a horse-animal, which happens to implement a transportation device interface. If you think it's a transportation device which happens to implement a horse interface, I can't help you :)

  Heheh, and I thought it's an animal that happens to have aggregated transportation device features ... damn, that's the franken-horse ...!

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  Solved Problem adapting a C code to Qt
  c code crash app ricker wavelet scientific comp • • Flavio Mesquita

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  @Flavio-Mesquita Then please mark this thread as solved.

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  Solved Strange LNK 2019 error in qt
  • Shaharyaar

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  I am currently using Qt 5.6.3

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  Unsolved unique_ptr question
  • adutzu89

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  @VRonin Oh, I was not taking unique_ptr into account as I removed it from my code.

  Thanks for your input though!

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  Unsolved instance of a struct
  • Digitale_GFacchini

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  @JonB said in istance of a struct:

  Even when you get this bit working, like I said I suspect your whole approach like now is not going to achieve what you want in the way of making these values available to every module, so you're going to have to do it a different way like I said anyway...

  Good evening, I'm sorry for my absence.
  It's true! The problem is a C ++ concept that I have been studying for a short time, together with QT. But those who use QT, if I understand correctly, also know C ++. For that I asked the question here. Apart from that, I think it's right that what you said also on the approach. I think that my intent must act in another way. the question is which one?

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  Unsolved Information about Ethernet over USB (RNDIS) in Qt
  qt creator c++ qt usb qt ethernet rndis • • cnmM

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  Sounds rather like a job for libusb

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  Solved struct and passing array parameters
  • Digitale_GFacchini

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  Thank SGaist

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  Solved Signal and Slots are not Working in my project
  • Shaharyaar

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  I think you misunderstand how signals/slots work.

  in your connect statement the first param is an object emitting a signal and the second one is a method (signal) of that object's class. Class QPushButton doesn't have a method (signal) named sayHello. It's a method (signal) in MainWindow class.

  QPushButton has a method (signal) named clicked(), so you can connect that. If you want to call pushed() when the button "Hi" is clicked then you connect like this:

  connect(ui->pushButton_2, &QPushButton::clicked, this, &MainWindow::pushed);

  If you want the main window to emit sayHello when the button "Hi" is pressed and then in response to that you want to call replyHi you make two connections:

  connect(ui->pushButton_2, &QPushButton::clicked, this, &MainWindow::sayHello); // emits sayHello when the button is clicked connect(this, &MainWindow::sayHello, this, &MainWindow::replyHi); // calls replyHi when sayHello is emitted
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  This topic is deleted!
  • mad-hatter

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