[Solved] QApplication: No such file or directory

sierdzio

How do you include QApplication header? In Qt5, it resides in <QtWidgets/QApplication>, while in Qt4 it was <QtGui/QApplication>.

Zlatomir

I think the module isn't added in .pro file, so did you added QT += widgets in your .pro file?

//anyway if the module is added the header can be included with #include <QApplication> you don't need <QtWidgets/QApplication> or <QtGui/QApplication> in Qt4 (that works with both Qt4 and 5)

jalomann

Adding QT += widgets in .pro file made the trick. Thanks.

Carel

Why does qmake not include these, or what must one do in the source to ensure qmake auto generates this line in the .pro file ?

sierdzio

qmake will never generate anything in your .pro file. Those files are config files for qmake to use, not the other way around. If you create a new project in recent versions of Qt Creator, this line will be added for you in standard app template.

Carel

Ooh ok, that make more sense now, thanks for the reply.

Sorry for hijacking the thread by the way :D

Iotaprime

The "Adding QT += widgets in .pro file" really helped me as well. Thanks.

realtebo

I'm happy, too. I solved.

Why qmake --project is doing a so simple task in a wrong way?

niboaix

can qmake -project add "QT += widgets" to .pro automatically ?

Pysis

Just to say what happened to be my problem, it was a dumb error:

I was following a guide that had me open an empty QT project, which gave me a .pro file but left it empty. I had filled in some data and "TEMPLATE = application" as they has mentioned it. I already had the "widgets" line but it still couldn't find the library as I included it in the .cpp file. When I changed it to "TEMPALTE = app" the .pro file was parsed, and the file to include resolved correctly (QApplication).

Mijaz

@sierdzio
I have add <QtWidgets/QApplication> to mainwindow.h file and
QT += widgets in .pro file but still "error : No such file or directory" occurs .

jsulm

@Mijaz said in [Solved] QApplication: No such file or directory:

<QtWidgets/QApplication>

It's

#include <QApplication>

Mijaz

@jsulm
I have changed but error still error not resolved.

jsulm

@Mijaz Please show your pro file and main.cpp

braden_sun

@jsulm Hello, I am having a similar issue to @Mijaz. I am trying to use Qt 5.11 to cross compile for a STM32MP157c-DK2 development board. I have successfully loaded images to the board from a qml file but my cpp files are riddled with errors including "use of undeclared identifier 'QCoreApplication'. I have tried adding #include <QApplication> and QT += widgets with no luck. Here is my main.cpp file and my pro file.

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include <QApplication>
#include <QLabel>

#include <QQmlEngine>
#include <QTextCodec>
#include <QtGui>

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

pro file

QT += quick widgets core gui

CONFIG += c++11 qmltypes qt

# The following define makes your compiler emit warnings if you use
# any Qt feature that has been marked deprecated (the exact warnings
# depend on your compiler). Refer to the documentation for the
# deprecated API to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
#qnx: target.path = /tmp/$${TARGET}/bin
#else: unix:!android: target.path = /opt/$${TARGET}/bin
#!isEmpty(target.path): INSTALLS += target
TARGET = stm32mp1Test
    target.files = stm32mp1Test
    target.path = /home/root
INSTALLS += target

Thanks for the help.

jsulm

@braden_sun Did you cross compile Qt for your device?
Why do you include QApplication and QGuiApplication if you want to use QCoreApplication? You need to include QCoreApplication...