Function parameters QML/C++

[alecs26]

Hello,

In order to communicate between my QML UI and my C++ code, I use ContextProperty.
For instance, in my main.cpp, I have my main function:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QQmlApplicationEngine engine;

    QQmlComponent componentmain(&engine,QUrl(QStringLiteral("qrc:/main.qml")));
    otherfunctions.objectmain=componentmain.create();

    QQmlContext* ctx = engine.rootContext();
    OtherFunctions otherfunctions;
    ctx->setContextProperty("otherfunctions", &otherfunctions);

    testmainfunc(otherfunctions); // explained later

    return app.exec();
}

From my QML code, I can access the functions from my class "otherfunctions". I can also access this class from my main function which is usefull to communicated between QML and C++.

However, in my main.cpp, I have another function that I call from the main function: testmainfunc(otherfunctions). As a parameter, I want to send my class "otherfunctions" so this function can modify parameters from "otherfunctions" and thus communicate with the QML code.

However, when I declare my function as "void testmainfunc(OtherFunctions otherfunctions);", I get the error :
"error: use of deleted function 'OtherFunctions::OtherFunctions(const OtherFunctions&)'"

If I declare my function as "void testmainfunc(OtherFunctions &otherfunctions);" [notice the &] it seems fine. For instance the following seems to work:

void testmainfunc(OtherFunctions &otherfunctions)
{
    otherfunctions.pathweb1insession="test1";
}

My question is

1. Why "void testmainfunc(OtherFunctions otherfunctions);" does not work ?
2. Is it OK to do as I did with "void testmainfunc(OtherFunctions &otherfunctions);" [notice the &] ?

Thank you very much for your help !

Alex

[dheerendra]

Your object is Qobject. You r passing the object by value. Copy constructor is disabled in qt. Hence you hit the error.

[jsulm]

@alecs26 To add to @dheerendra : if you want a function which modifies its parameter then you should pass this parameter as reference (&) or pointer (*), else your function will modify a copy! Read about passing parameters "by value", "by reference" and pointer in C++.

[alecs26]

@jsulm
Thank you for you answer.

So is it OK to do that:
in the main call: testmainfunc(otherfunctions);

and the function:
void testmainfunc(OtherFunctions &otherfunctions)
{
otherfunctions.pathweb1insession="test1";
}

Thank you !

Alex

[jsulm]

@alecs26 Actually you can answer your own question by just trying it out.
But, yes passing by reference will work.

[dheerendra]

Yes it is ok as you r passing the object by reference.

[alecs26]

@jsulm @dheerendra
Thank you for your answer.

@jsulm Yes I tried it and it worked but I wanted to be sure it was a proper way to do it.

Thank you both very much !

Alex