Error QApplication no such file or directory

Question

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

User · Answer

In Qt5 you should use QtWidgets instead of QtGui   include  lt QtGui QComboBox gt         incorrect in QT5  include  lt QtWidgets QComboBox gt        correct in QT5   Or   include  lt QtGui QStringListModel gt        incorrect in QT5  include  lt QtCore QStringListModel gt        correct in QT5

User · Answer

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

User · Answer

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  lt QtGui QApplication gt     with     include  lt QApplication gt

User · Answer

In Qt 5 you now have to add widgets to the QT qmake variable  in your MyProject pro file     QT    widgets

User · Answer

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  amp  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

User · Answer

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

User · Answer

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

User · Answer

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  lt version-here gt  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 lt version gt  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  lt QtWidgets QApplication gt  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 lt version gt  64 lib gcc x86 64-w64-mingw32 7 3 0 include c   iostream

User · Answer

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

User · Answer

To start things off  the error QApplication  no such file or directory means your compiler was not able to find this header  It is not related to the linking process as you mentioned in the question   The -I flag  uppercase i  is used to specify the include  headers  directory  which is what you need to do   while the -L flag is used to specify the libraries directory  The -l flag  lowercase L  is used to link your application with a specified library   But you can use Qt to your advantage  Qt has a build system named qmake which makes things easier  For instance  when I want to compile main cpp I create a main pro file  For educational purposes  let s say this source code is a simple project that uses only QApplication and QDeclarativeView  An appropriate  pro file would be   TEMPLATE    app QT    gui declarative SOURCES    main cpp   Then  execute the qmake inside that directory to create the Makefile that will be used to compile your application  and finally execute make to get the job done   On my system this make outputs   g   -c -pipe -O2 -Wall -W -D REENTRANT -DQT NO DEBUG -DQT DECLARATIVE LIB -DQT GUI LIB -DQT CORE LIB -DQT SHARED -I opt qt 47x mkspecs linux-g   -I  -I opt qt 47x include QtCore -I opt qt 47x include QtGui -I opt qt 47x include QtDeclarative -I opt qt 47x include -I usr X11R6 include -I  -o main o main cpp g   -Wl -O1 -Wl -rpath  opt qt 47x lib -o main main o -L opt qt 47x lib -L usr X11R6 lib -lQtDeclarative -L opt qt 47x lib -lQtScript -lQtSvg -L usr X11R6 lib -lQtSql -lQtXmlPatterns -lQtNetwork -lQtGui -lQtCore -lpthread   Note  I installed Qt in another directory --   opt qt 47x  Edit  Qt 5 x and later  Add QT    widgets to the  pro file and solve this problem

User · Answer

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

[c++] Error QApplication: no such file or directory

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