I have installed C++SDK that have Qt but when I try compiling a code linking QApplication it gives me the error:
Error QApplication: no such file or directory
How do I link these libraries? I searched into the directories and there is a file named QApplication.h; So I tried to link it with -I (linking the directory) but it was still giving me that error.
Please make sure that the version of qmake you are using corresponds to the version of QT you want to use.
To be sure, you can just run :
$qmake -v
Your problem seems to be a symptom of a version conflict between QT 3 and 4, as can be seen here :
http://lists.trolltech.com/qt4-preview-feedback/2005-11/thread00013-0.html
To fix this, you can either delete your old install of QT, or specifically point to qmake-qt4 in your Makefile.
You can change build versiyon.For example i tried QT 5.6.1 but it didn't work.Than i tried QT 5.7.0 .So it worked , Good Luck! :)
In Qt 5 you now have to add widgets to the QT qmake variable (in your MyProject.pro file).
QT += widgets
For QT 5
Step1:
.pro (in pro file, add these 2 lines)
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
Step2:
In main.cpp replace code:
#include <QtGui/QApplication>
with:
#include <QApplication>
you have to add QT +=widgets in the .pro file before the first execution, if you execute before adding this line its not gonna working, so yo need to start file's creation from the beginning.
Looks like you don't have the development libraries installed. Install them using:
sudo apt-get install libqt4-dev
As you said int the comments that you have them installed, just re-install it. Now. to update the locate's database, issue this command $sudo updatedb
Then $locate QApplication to check that you now have the header file installed.
Now, goto the the folder where you have the code & type these commands
qmake -project
qmake
make
Then you can find the binary created.
Alternatively, you can use Qt Creator if you want the GUI.
See the official documentation for more info. http://developer.qt.nokia.com/doc/qt-4.8/gettingstartedqt.html
To learn how to use Qt Creator, use http://doc.qt.nokia.com/qtcreator-2.2/creator-qml-application.html
I suggest you to update your SDK and start new project and recompile everything you have. It seems you have some inner program errors. Or you are missing package.
And ofc do what Abdijeek said.
Make sure you have qmake in your path (which qmake), and that it works (qmake -v) (IF you have to kill it with ctr-c then there is something wrong with your environment).
Then follow this: http://developer.qt.nokia.com/doc/qt-4.8/gettingstartedqt.html
Well, It's a bit late for this but I've just started learning Qt and maybe this could help somebody out there:
If you're using Qt Creator then when you've started creating the project you were asked to choose a kit to be used with your project, Let's say you chose Desktop Qt <version-here> MinGW 64-bit. For Qt 5, If you opened the Qt folder of your installation, you'll find a folder with the version of Qt installed as its name inside it, here you can find the kits you can choose from.
You can go to /PATH/FOR/Qt/mingw<version>_64/include and here you'll find all the includes you can use in your program, just search for QApplication and you'll find it inside the folder QtWidgets, So you can use #include <QtWidgets/QApplication> since the path starts from the include folder.
The same goes for other headers if you're stuck with any and for other kits.
Note: "all the includes you can use" doesn't mean these are the only ones you can use, If you include iostream for example then the compiler will include it from /PATH/FOR/Qt/Tools/mingw<version>_64/lib/gcc/x86_64-w64-mingw32/7.3.0/include/c++/iostream
In Qt5 you should use QtWidgets instead of QtGui
#include <QtGui/QComboBox> // incorrect in QT5
#include <QtWidgets/QComboBox> // correct in QT5
Or
#include <QtGui/QStringListModel> // incorrect in QT5
#include <QtCore/QStringListModel> // correct in QT5
Source: Stackoverflow.com