[Solved] QApplication: No such file or directory

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...