Qt DECLARATIVE_EXAMPLE_MAIN means what?

**Mike_m** · 27th June 2017, 09:37

I wanted to look at an example C++ code that came with Qt software.
I looked at main.cpp file at following path:

Qt Code:

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C:\Qt\Examples\Qt-5.9\quick\threading

C:\Qt\Examples\Qt-5.9\quick\threading

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This main.cpp has following two lines:

Qt Code:

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#include "../shared/shared.h"
DECLARATIVE_EXAMPLE_MAIN(threading/threading)

#include "../shared/shared.h"
DECLARATIVE_EXAMPLE_MAIN(threading/threading)

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What this DECLARATIVE_EXAMPLE_MAIN means?
Is there a way to look at this main.cpp's C++ source code and understand features of this main program
please?
Thanks

**Mike_m** · 28th June 2017, 12:09

I found answer to what DECLARATIVE_EXAMPLE_MAIN means?
This is a macro defined in the following shared.h file.

Qt Code:

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// C:\Qt\Examples\Qt-5.9\quick\shared\shared.h
 
#define DECLARATIVE_EXAMPLE_MAIN(NAME) int main(int argc, char* argv[]) \
{\
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);\
    QGuiApplication app(argc,argv);\
    app.setOrganizationName("QtProject");\
    app.setOrganizationDomain("qt-project.org");\
    app.setApplicationName(QFileInfo(app.applicationFilePath()).baseName());\
    QQuickView view;\
    if (qgetenv("QT_QUICK_CORE_PROFILE").toInt()) {\
        QSurfaceFormat f = view.format();\
        f.setProfile(QSurfaceFormat::CoreProfile);\
        f.setVersion(4, 4);\
        view.setFormat(f);\
    }\
    view.connect(view.engine(), &QQmlEngine::quit, &app, &QCoreApplication::quit);\
    new QQmlFileSelector(view.engine(), &view);\
    view.setSource(QUrl("qrc:///" #NAME ".qml")); \
    if (view.status() == QQuickView::Error)\
        return -1;\
    view.setResizeMode(QQuickView::SizeRootObjectToView);\
    if (QGuiApplication::platformName() == QLatin1String("qnx") || \
          QGuiApplication::platformName() == QLatin1String("eglfs")) {\
        view.showFullScreen();\
    } else {\
        view.show();\
    }\
    return app.exec();\
}

// C:\Qt\Examples\Qt-5.9\quick\shared\shared.h

#define DECLARATIVE_EXAMPLE_MAIN(NAME) int main(int argc, char* argv[]) \
{\
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);\
    QGuiApplication app(argc,argv);\
    app.setOrganizationName("QtProject");\
    app.setOrganizationDomain("qt-project.org");\
    app.setApplicationName(QFileInfo(app.applicationFilePath()).baseName());\
    QQuickView view;\
    if (qgetenv("QT_QUICK_CORE_PROFILE").toInt()) {\
        QSurfaceFormat f = view.format();\
        f.setProfile(QSurfaceFormat::CoreProfile);\
        f.setVersion(4, 4);\
        view.setFormat(f);\
    }\
    view.connect(view.engine(), &QQmlEngine::quit, &app, &QCoreApplication::quit);\
    new QQmlFileSelector(view.engine(), &view);\
    view.setSource(QUrl("qrc:///" #NAME ".qml")); \
    if (view.status() == QQuickView::Error)\
        return -1;\
    view.setResizeMode(QQuickView::SizeRootObjectToView);\
    if (QGuiApplication::platformName() == QLatin1String("qnx") || \
          QGuiApplication::platformName() == QLatin1String("eglfs")) {\
        view.showFullScreen();\
    } else {\
        view.show();\
    }\
    return app.exec();\
}

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**d_stranz** · 28th June 2017, 17:07

And do you understand what it does?

**Mike_m** · 30th June 2017, 07:02

To understand what it does, I replaced macro with its equivalent C++ program as follows:

Qt Code:

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#include <QDir>
#include <QGuiApplication>
#include <QQmlEngine>
#include <QQmlFileSelector>
#include <QQuickView>
 
int main(int argc, char* argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc,argv);
    app.setOrganizationName("QtProject");
    app.setOrganizationDomain("qt-project.org");
    app.setApplicationName(QFileInfo(app.applicationFilePath()).baseName());
    QQuickView view;
    if (qgetenv("QT_QUICK_CORE_PROFILE").toInt()) {
        QSurfaceFormat f = view.format();
        f.setProfile(QSurfaceFormat::CoreProfile);
        f.setVersion(4, 4);
        view.setFormat(f);
    }
    view.connect(view.engine(), &QQmlEngine::quit, &app, &QCoreApplication::quit);
    new QQmlFileSelector(view.engine(), &view);
    view.setSource(QUrl("qrc:///threading/threading.qml"));
    if (view.status() == QQuickView::Error)
        return -1;
    view.setResizeMode(QQuickView::SizeRootObjectToView);
    if (QGuiApplication::platformName() == QLatin1String("qnx") ||
          QGuiApplication::platformName() == QLatin1String("eglfs")) {
        view.showFullScreen();
    } else {
        view.show();
    }
    return app.exec();
}

#include <QDir>
#include <QGuiApplication>
#include <QQmlEngine>
#include <QQmlFileSelector>
#include <QQuickView>

int main(int argc, char* argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc,argv);
    app.setOrganizationName("QtProject");
    app.setOrganizationDomain("qt-project.org");
    app.setApplicationName(QFileInfo(app.applicationFilePath()).baseName());
    QQuickView view;
    if (qgetenv("QT_QUICK_CORE_PROFILE").toInt()) {
        QSurfaceFormat f = view.format();
        f.setProfile(QSurfaceFormat::CoreProfile);
        f.setVersion(4, 4);
        view.setFormat(f);
    }
    view.connect(view.engine(), &QQmlEngine::quit, &app, &QCoreApplication::quit);
    new QQmlFileSelector(view.engine(), &view);
    view.setSource(QUrl("qrc:///threading/threading.qml"));
    if (view.status() == QQuickView::Error)
        return -1;
    view.setResizeMode(QQuickView::SizeRootObjectToView);
    if (QGuiApplication::platformName() == QLatin1String("qnx") ||
          QGuiApplication::platformName() == QLatin1String("eglfs")) {
        view.showFullScreen();
    } else {
        view.show();
    }
    return app.exec();
}

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This program gave following output:

thread_program_output.PNG

In the next post, I will explain this program and its output.

**d_stranz** · 30th June 2017, 17:43

Good. The purpose of the macro is to give the developers of QML examples the ability to write a "boilerplate" driver program, where all of the differences between examples are in the QML that the driver loads in the "view.setSource()" line 23. The driver is identical in all examples, what is different is only in the QML.

**Mike_m** · 1st July 2017, 03:19

d_stranz,
Thank you for information about line 23.
I quickly searched all example programs and found following is list of example programs this boilerplate driver is being used:

Qt Code:

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DECLARATIVE_EXAMPLE_MAIN(qml/xmlhttprequest/xmlhttprequest)
DECLARATIVE_EXAMPLE_MAIN(animation/animation)
DECLARATIVE_EXAMPLE_MAIN(canvas/canvas)
DECLARATIVE_EXAMPLE_MAIN(dialcontrol)
DECLARATIVE_EXAMPLE_MAIN(demos/calqlatr/calqlatr)
DECLARATIVE_EXAMPLE_MAIN(demos/clocks/clocks)
DECLARATIVE_EXAMPLE_MAIN(demos/maroon/maroon)
DECLARATIVE_EXAMPLE_MAIN(demos/rssnews/rssnews)
DECLARATIVE_EXAMPLE_MAIN(demos/samegame/samegame)
DECLARATIVE_EXAMPLE_MAIN(demos/stocqt/stocqt)
DECLARATIVE_EXAMPLE_MAIN(demos/tweetsearch/tweetsearch)
DECLARATIVE_EXAMPLE_MAIN(draganddrop/draganddrop)
DECLARATIVE_EXAMPLE_MAIN(externaldraganddrop/externaldraganddrop)
DECLARATIVE_EXAMPLE_MAIN(imageelements/imageelements)
DECLARATIVE_EXAMPLE_MAIN(keyinteraction/keyinteraction)
DECLARATIVE_EXAMPLE_MAIN(mousearea/mousearea)
DECLARATIVE_EXAMPLE_MAIN(particles/affectors/affectors)
DECLARATIVE_EXAMPLE_MAIN(particles/customparticle/customparticle)
DECLARATIVE_EXAMPLE_MAIN(particles/emitters/emitters)
DECLARATIVE_EXAMPLE_MAIN(particles/imageparticle/imageparticle)
DECLARATIVE_EXAMPLE_MAIN(particles/system/system)
DECLARATIVE_EXAMPLE_MAIN(positioners/positioners)
DECLARATIVE_EXAMPLE_MAIN(accessibility/accessibility)
DECLARATIVE_EXAMPLE_MAIN(righttoleft/righttoleft)
DECLARATIVE_EXAMPLE_MAIN(shadereffects/shadereffects)
DECLARATIVE_EXAMPLE_MAIN(text/text)
DECLARATIVE_EXAMPLE_MAIN(threading/threading)
DECLARATIVE_EXAMPLE_MAIN(touchinteraction/touchinteraction)
DECLARATIVE_EXAMPLE_MAIN(views/views)

DECLARATIVE_EXAMPLE_MAIN(qml/xmlhttprequest/xmlhttprequest)
DECLARATIVE_EXAMPLE_MAIN(animation/animation)
DECLARATIVE_EXAMPLE_MAIN(canvas/canvas)
DECLARATIVE_EXAMPLE_MAIN(dialcontrol)
DECLARATIVE_EXAMPLE_MAIN(demos/calqlatr/calqlatr)
DECLARATIVE_EXAMPLE_MAIN(demos/clocks/clocks)
DECLARATIVE_EXAMPLE_MAIN(demos/maroon/maroon)
DECLARATIVE_EXAMPLE_MAIN(demos/rssnews/rssnews)
DECLARATIVE_EXAMPLE_MAIN(demos/samegame/samegame)
DECLARATIVE_EXAMPLE_MAIN(demos/stocqt/stocqt)
DECLARATIVE_EXAMPLE_MAIN(demos/tweetsearch/tweetsearch)
DECLARATIVE_EXAMPLE_MAIN(draganddrop/draganddrop)
DECLARATIVE_EXAMPLE_MAIN(externaldraganddrop/externaldraganddrop)
DECLARATIVE_EXAMPLE_MAIN(imageelements/imageelements)
DECLARATIVE_EXAMPLE_MAIN(keyinteraction/keyinteraction)
DECLARATIVE_EXAMPLE_MAIN(mousearea/mousearea)
DECLARATIVE_EXAMPLE_MAIN(particles/affectors/affectors)
DECLARATIVE_EXAMPLE_MAIN(particles/customparticle/customparticle)
DECLARATIVE_EXAMPLE_MAIN(particles/emitters/emitters)
DECLARATIVE_EXAMPLE_MAIN(particles/imageparticle/imageparticle)
DECLARATIVE_EXAMPLE_MAIN(particles/system/system)
DECLARATIVE_EXAMPLE_MAIN(positioners/positioners)
DECLARATIVE_EXAMPLE_MAIN(accessibility/accessibility)
DECLARATIVE_EXAMPLE_MAIN(righttoleft/righttoleft)
DECLARATIVE_EXAMPLE_MAIN(shadereffects/shadereffects)
DECLARATIVE_EXAMPLE_MAIN(text/text)
DECLARATIVE_EXAMPLE_MAIN(threading/threading)
DECLARATIVE_EXAMPLE_MAIN(touchinteraction/touchinteraction)
DECLARATIVE_EXAMPLE_MAIN(views/views)

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