--icon option doesn't work with QApplication in Qt > 5.5

JoshThunar

I want to display the command line argument, that user provided for the application, f.e.:

./ToolOne --name

When I'm trying to get the argument from QApplication object within Qt 5.3.2 everything works. However, after using Qt 5.6.1 or 5.11.3, everything works, except the option

--icon

Any other word is working, no matter if -i or --ico. Except for --icon... Somehow, when this argument is consumed by the QApplication() it disappears.

My main function:

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QStringList arguments = a.arguments(); 
    // If argv has --icon, under Qt >= 5.6, arguments list will NOT contain icon

    MainWindow w( arguments.join(" ") );
    w.show();

    return a.exec();
}

--icon argument simply disappears in the QApplication constructor. What is worth to mention is that when I'm using QCoreApplication it works perfectly under all systems.

I tried to find any special handling in Qt or any bug report but with no result. If that matters I've checked it on:

CentOS 6 with Qt 5.3.2 and gcc: 4.8.2 (works)
RedHat 6 with Qt 5.3.2 and gcc: 4.7.2 (works)
RedHat 6 with Qt 5.6.1 and gcc 4.7.1 (fails)
RedHat 6 with Qt 5.6.1 and gcc 4.9.1 (fails)
CentOS 7 with Qt 5.9.2 and gcc 4.8.5 (fails)
RedHat 7 with Qt 5.3.2 and gcc 4.8.5 (works)
Fedora 29 with Qt 5.11.3 and gcc 8.2.1 (fails)

Link with small example:
https://drive.google.com/drive/folders/1TGJIbzTkotnHbymTC3xDa-0PFAfG1w4n?usp=sharing

JoshThunar

I've received an answer on Stack Overflow. It looks like in Qt 5.4 there was a change related with XCB handling that is not shown in the documentation:

https://stackoverflow.com/questions/54553876/icon-option-doesnt-work-with-qapplication-in-qt-5-5

In the documentation it is stated, that f.e. user can use -geometry same as -qwindowgeometry but only -qwindowicon is visible in the documentation.

http://doc.qt.io/qt-5/qguiapplication.html#QGuiApplication

In code we can see, that -icon is also recognised on XCB platform:
http://code.qt.io/cgit/qt/qtbase.git/tree/src/gui/kernel/qguiapplication.cpp?h=5.5#n1164