C1083: Cannot open include file: 'QApplication'

Hello,

I'm very new to Qt.
I just installled Qt5.0.0 & MS Visual C++ Comilper 10.0 on my compuer (running Win7)

I tried to compile and run a few programs from the Qt Creator Examples. They work.

Then, I created a very simple project using "Empty Qt project" from Qt Creator.
The project was created at the default location "C:\Qt\Qt5.0.0\Tools\QtCreator\bin"
I just added one main.cpp source file with the following code:

Code:

---

#include <QApplication>
#include <QPushButton>
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QPushButton button("Run");
    button.show()
    return app.exec
}

---

I tried to compile it. It didn't work and it gave me: C1083: Cannot open include file: 'QApplication'.

I looked up on the forum for similar issues and someone said: "Add the folder of the Qt include files to the paths that are used for finding headers."
I added it to the project file (.pro), so now it looks like this:

Code:

---

INCLUDEPATH = C:\Qt\Qt5.0.0\5.0.0\msvc2010\include
SOURCES += \
    main.cpp

---

but it still doesn't work...Any idea to help me with this very basic code? :(

Thank you in advance!

Add the following to your project file:

Code:

---

QT += widgets

---

Thanks wysota.

I did it, so my project file looks like this:

Code:

---

QT += widgets
SOURCES += \
    main.cpp

---

I tryed to compile without modifying the main.cpp and I got the exact same error.
I figured out that I actually had to write:

Code:

---

#include <QtWidgets/QApplication>
#include <QtWidgets/QPushButton>

---

instead of:

Code:

---

#include <QApplication>
#include <QPushButton>

---

for it to work.

What I still don't understand is that the examples given in Qt creator use

Code:

---

#include <QApplication>

---

and they compile without complaining.

You neither need nor want the "QtWidgets/" portion of those #include lines; but you do need to rerun qmake after modifying the PRO file.

Thank you very much CrisW67! It works just fine. My error was that I thought that pressing the run button in Qt creator would both run qmake and compile the code.

Hi everybody, I have the same problem, I did add

Code:

---

QT += widgets

---

and rerun the qmake and rebuild.
What I get is no errors ,but when I run the project it says The program has unexpectedly finished. and in the compile output this line C:\Qt\Qt5.0.1\Tools\QtCreator\bin\jom.exe -f Makefile.Debug is colored in red

Your code is the problem. Launch your program in your debugger and, when it crashes, look at the information available to work out where and why it crashes. If you still cannot work it out then start your own thread and actually provide some information about your program, where it is crashing, what you have tried to diagnose/fix it etc. We are not mind readers and need at least some information to go on.

It worked, The error was that I used a QCoreApplication object instead of QApplication , my bad sorry ;)

QT +=widgets is one of assignment to qmake variable. qmake has following variables for your reference.
CONFIG
DEFINES
DEF_FILE
DEPENDPATH
DEPLOYMENT
DEPLOYMENT_PLUGIN
DESTDIR
DESTDIR_TARGET
DLLDESTDIR
DISTFILES
FORMS
GUID
HEADERS
ICON
INCLUDEPATH
INSTALLS
LEXIMPLS
LEXOBJECTS
LEXSOURCES
LIBS
LITERAL_HASH
MAKEFILE
MAKEFILE_GENERATOR
MOC_DIR
OBJECTS
OBJECTS_DIR
OBJMOC
POST_TARGETDEPS
PRE_TARGETDEPS
PRECOMPILED_HEADER
PWD
OUT_PWD
QMAKE
QMAKESPEC
QMAKE_APP_FLAG
QMAKE_APP_OR_DLL
QMAKE_AR_CMD
QMAKE_BUNDLE_DATA
QMAKE_BUNDLE_EXTENSION
QMAKE_CC
QMAKE_CFLAGS_DEBUG
QMAKE_CFLAGS_RELEASE
QMAKE_CFLAGS_SHLIB
QMAKE_CFLAGS_THREAD
QMAKE_CFLAGS_WARN_OFF
QMAKE_CFLAGS_WARN_ON
QMAKE_CLEAN
QMAKE_CXX
QMAKE_CXXFLAGS
QMAKE_CXXFLAGS_DEBUG
QMAKE_CXXFLAGS_RELEASE
QMAKE_CXXFLAGS_SHLIB
QMAKE_CXXFLAGS_THREAD
QMAKE_CXXFLAGS_WARN_OFF
QMAKE_CXXFLAGS_WARN_ON
QMAKE_DISTCLEAN
QMAKE_EXTENSION_SHLIB
QMAKE_EXT_MOC
QMAKE_EXT_UI
QMAKE_EXT_PRL
QMAKE_EXT_LEX
QMAKE_EXT_YACC
QMAKE_EXT_OBJ
QMAKE_EXT_CPP
QMAKE_EXT_H
QMAKE_EXTRA_COMPILERS
QMAKE_EXTRA_TARGETS
QMAKE_FAILED_REQUIREMENTS
QMAKE_FRAMEWORK_BUNDLE_NAME
QMAKE_FRAMEWORK_VERSION
QMAKE_INCDIR
QMAKE_INCDIR_EGL
QMAKE_INCDIR_OPENGL
QMAKE_INCDIR_OPENGL_ES1, QMAKE_INCDIR_OPENGL_ES2
QMAKE_INCDIR_OPENVG
QMAKE_INCDIR_QT
QMAKE_INCDIR_THREAD
QMAKE_INCDIR_X11
QMAKE_INFO_PLIST
QMAKE_LFLAGS
QMAKE_LFLAGS_CONSOLE
QMAKE_LFLAGS_DEBUG
QMAKE_LFLAGS_PLUGIN
QMAKE_LFLAGS_RPATH
QMAKE_LFLAGS_QT_DLL
QMAKE_LFLAGS_RELEASE
QMAKE_LFLAGS_SHAPP
QMAKE_LFLAGS_SHLIB
QMAKE_LFLAGS_SONAME
QMAKE_LFLAGS_THREAD
QMAKE_LFLAGS_WINDOWS
QMAKE_LIBDIR
QMAKE_LIBDIR_FLAGS
QMAKE_LIBDIR_EGL
QMAKE_LIBDIR_OPENGL
QMAKE_LIBDIR_OPENVG
QMAKE_LIBDIR_QT
QMAKE_LIBDIR_X11
QMAKE_LIBS
QMAKE_LIBS_EGL
QMAKE_LIBS_OPENGL
QMAKE_LIBS_OPENGL_QT
QMAKE_LIBS_OPENGL_ES1, QMAKE_LIBS_OPENGL_ES2
QMAKE_LIBS_OPENVG
QMAKE_LIBS_QT
QMAKE_LIBS_QT_DLL
QMAKE_LIBS_QT_OPENGL
QMAKE_LIBS_QT_THREAD
QMAKE_LIBS_RT
QMAKE_LIBS_RTMT
QMAKE_LIBS_THREAD
QMAKE_LIBS_WINDOWS
QMAKE_LIBS_X11
QMAKE_LIB_FLAG
QMAKE_LINK_SHLIB_CMD
QMAKE_LN_SHLIB
QMAKE_POST_LINK
QMAKE_PRE_LINK
QMAKE_PROJECT_NAME
QMAKE_MAC_SDK
QMAKE_MACOSX_DEPLOYMENT_TARGET
QMAKE_MAKEFILE
QMAKE_MOC_SRC
QMAKE_QMAKE
QMAKE_QT_DLL
QMAKE_RESOURCE_FLAGS
QMAKE_RPATH
QMAKE_RPATHDIR
QMAKE_RUN_CC
QMAKE_RUN_CC_IMP
QMAKE_RUN_CXX
QMAKE_RUN_CXX_IMP
QMAKE_TARGET
QMAKE_UIC
QT
QTPLUGIN
QT_VERSION
QT_MAJOR_VERSION
QT_MINOR_VERSION
QT_PATCH_VERSION
RC_FILE
RC_INCLUDEPATH
RCC_DIR
REQUIRES
RESOURCES
RES_FILE
SIGNATURE_FILE
SOURCES
SRCMOC
SUBDIRS
TARGET
TARGET_EXT
TARGET_x
TARGET_x.y.z
TEMPLATE
TRANSLATIONS
UICIMPLS
UICOBJECTS
UI_DIR
UI_HEADERS_DIR
UI_SOURCES_DIR
VERSION
VER_MAJ
VER_MIN
VER_PAT
VPATH
YACCIMPLS
YACCOBJECTS
YACCSOURCES
_PRO_FILE_
_PRO_FILE_PWD_