Lost my QApplication

  • Doing Qt C++ in Win 7.

    I somehow am getting an error that I cannot open include file QApplicaiton -- I am following a YouTube tutorial. Help cannot find QApplicaiton either, so I suspect it has been superceded by something. How do I find out what? I'm a total novice, new to C++ and Qt. Also my knowledge of Windows esoterica is limited as well.

  • @astroannie
    Hi and welcome to devnet

    You do not give enough details. However, it may be your virus checker playing a role. I have had similar cases that I could start my application and the next moment I could not. The executable was gone.

    If this is not the case, you need to give some details about your setup and which tutorial you are following.

  • Okay, the tutorial is C++ Qt Programming by VoidRealms -- I don't know how to get the nitty-gritty on which Qt I'm using except I downloaded it Tuesday so it's pretty new. (Help > About tells about QtCreator). And yes, I'm running Avast.

    It's not my executable -- that one I can fix by logging out and logging back in again. This is an error where it says that it can't open QApplication Here's the code:

    #include <QApplication>
    #include <QLabel>
    int main(int argc, char *argv[])
        QApplication app(argc, argv);
        QLabel *label = new QLabel("Hello world");
        return app.exec();

    ... and here's the error:
    C:\QtWorkspace\minimal\main.cpp:1: error: C1083: Cannot open include file: 'QApplications': No such file or directory

    Is this more helpful?

  • Lifetime Qt Champion

    Do you have a project file ?
    Its often called a .pro
    in that file, you might need
    QT += core gui

    You can also test by selecting new from menu and create new GUI application.
    (just next next it)
    Then run it.
    If that works, your Qt is fine.

  • Sorry, it's QApplication -- no s -- I typed it instead of copy/paste. I learned though -- here's my .pro file

    QT += core gui
    SOURCES += \

  • Lifetime Qt Champion

    ahh. ok. good catch :)

  • I told Avast to exclude my workspace. It's still not being able to find the QApplication -- same message. I even tried restarting to no avail.

    (I didn't realize you could copy/paste errors -- my old IDE was wonky about that). Here is what it really says, copy/pasted for your convenience:

    C:\QtWorkspace\minimal\main.cpp:1: error: C1083: Cannot open include file: 'QApplication': No such file or directory

  • @astroannie
    You are using Qt creator as your new IDE?
    You have the setup from your install process for Qt?

    In Qt creator go to menu "Tools" -> "Options" -> "Build&Run" what can you see under the different tabs?
    Are there some warnings?

  • @koahnig
    Okay, I looked.

    My compiler is (not copy/pastable) Microsoft Visual C++ 10.0 (x86).

    My Qt versions are 5.4.2 and 5.5.1 (both). Would removing one help?

    The only thing I have warnings on is Kits -- which I didn't know I even had. They have little triangles with ! in them. One is Qt5.4.2 MSVC2010 OpenGL 32bit and the other is Qt5.5.1 MSVC2010 32-bit (default)

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    You are missing QT += widgets in your .pro file.

    With Qt 5, the widgets have moved into their own module.

  • Bless you sir, I regret that I can thumb you up but the once.

  • Lifetime Qt Champion

    No worries for that :)

    Since you have it 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 :)