QCommandLineParser inheritance and vector problem.

[Khamza]

So, i wanted to inherit QCommandLineParser to save all option logic in my own class.
This is small example:

#include <QCommandLineParser>
class CommandLineParser : public QCommandLineParser
{
public:
    CommandLineParser()
    {
        QCommandLineOption *option = new QCommandLineOption("Option");
        addOption(*option);
       //^ - WARNING HERE
    }
private:
    QVector<QCommandLineOption *> options;
};

This gives me warning but compiles and works fine:

error: cannot initialize object parameter of type 'QCommandLineParser' with an expression of type 'CommandLineParser'

But if i change QVector to std::vector or QList it gives no warnings and also works fine.
I thought maybe problem is that in QCommandLineOption declaration used Q_DISABLE_COPY(QCommandLineOption). But as i said despite this i can use QList.

So, my question is why using QVector<QCommandLineOption *> options; gives me this warning?

Thanks in advance.
P.S using Qt Creator, Qt 5.

[jsulm]

@Khamza said in QCommandLineParser inheritance and vector problem.:

but may it be UB?

Do you mean undefined behavior? Why should it be?
As I said: this error comes from code model, not from the compiler when you compile your project. Code model can generate false positive errors/warnings. Important is what the compiler says when you compile.

[jsulm]

@Khamza You should call QCommandLineParser constructor in CommandLineParser constructor

[Khamza]

@jsulm I tried. Same result...

[jsulm]

@Khamza said in QCommandLineParser inheritance and vector problem.:

QCommandLineOption *option = new QCommandLineOption("Option");

Any reason you're allocating on the heap?

Please show how you're calling the base constructor.
I see no reason why the type of options member would cause this error. Try to rename options - not sure there is a property with this name in QCommandLineParser.

[Khamza]

@jsulm

class CommandLineParser : public QCommandLineParser
{
public:
    CommandLineParser()
        : QCommandLineParser()
    {
        QCommandLineOption *option = new QCommandLineOption("Option");
        addOption(*option);
    }
private:
    QVector<QCommandLineOption *> options;
};

int main(int argc, char** argv) {
    QApplication a(argc, argv);
    MainWindow w;
    
    w.show();
    return a.exec();
}

Use heap allocation to freely use option in class without many copyings.
Besides can it be IDE mistake?
P.S renaming option also didn't help...

[JonB]

@Khamza said in QCommandLineParser inheritance and vector problem.:

Besides can it be IDE mistake?

Where are you getting the

error: cannot initialize object parameter of type 'QCommandLineParser' with an expression of type 'CommandLineParser'

from? You say "This gives me warning but compiles and works fine", so I don't really understand. You get this at runtime, or what?

FWIW: At Qt6 QVector is gone, it just becomes QList. If you say your code works or doesn't warn with QList instead of QVector you could replace and pretend you never saw this issue. :)

[Khamza]

@JonB

Red stripes due to git

[jsulm]

@Khamza Please post code as text, not pictures.
This comes from code model I guess. Does your project compile?

"Use heap allocation to freely use option in class without many copyings" - why do you think there is less copying if you allocate it on the heap? You are passing it by reference, not pointer.

[Khamza]

@jsulm Sorry for that. Yes project compiles and runs. And QCommandLineParser functions also work.
P.S Regarding heap allocation, I realized that I was wrong

[jsulm]

@Khamza Then that error is a false positive from the code model and you can ignore it.

[Khamza]

@jsulm
This

class CommandLineParser : public QCommandLineParser
{
public:
    CommandLineParser(QApplication &a)
        : QCommandLineParser()
    {
        QCommandLineOption option = QCommandLineOption("option", "this is description", "argument");
        addHelpOption(); // main.cpp:38:9: error: cannot initialize object parameter of type 'QCommandLineParser' with an expression of type 'CommandLineParser'
        addVersionOption(); // same here
        addOption(option); // same here
        process(a);
        qInfo() << "Names: " << optionNames(); // same here
        qInfo() << "Is set:" << isSet(option) << value(option); // also here
    }
public:
    QVector<QCommandLineOption *> options;
//    QList<QCommandLineOption *> options;
};

int main(int argc, char** argv) {
    QApplication a(argc, argv);
    MainWindow w;
    CommandLineParser parser(a);
    w.show();
    return a.exec();
}

gives me

Names:  ("option")
Is set: true "asd"

So, as you see works fine. You say it's false positive, but may it be UB?

[jsulm]

@Khamza said in QCommandLineParser inheritance and vector problem.:

but may it be UB?

Do you mean undefined behavior? Why should it be?
As I said: this error comes from code model, not from the compiler when you compile your project. Code model can generate false positive errors/warnings. Important is what the compiler says when you compile.

[Khamza]

@jsulm
Ok, got it. Thanks a lot.
P.S
So, i thought that that i need my options must "live" when use parser.process(). But internally QLineOptionParser copies all option to QList<QCommandLineOption> commandLineOptionList; so i simply remove that vector...

[SGaist]

Hi,

@Khamza said in QCommandLineParser inheritance and vector problem.:

@jsulm

class CommandLineParser : public QCommandLineParser
{
public:
    CommandLineParser()
        : QCommandLineParser()
    {
        QCommandLineOption *option = new QCommandLineOption("Option");
        addOption(*option);
    }

One small side note: there's no need to allocate the option on the heap. You are just adding a layer of indirection for no benefit.

[JonB]

@Khamza
Just to wrap up.

• I think you are going to get rid of the new, so it does not matter now, but be aware that the way you wrote will leak the created QCommandLineOption. You assign to local variable and do not delete it. It would show up if you used e.g. valgrind.

• The message you get is only from the code model, and seems inexplicable. Which model are you using? If it's the internal one that no longer gets any attention and might be "off". You might wish to check if you are using the clang code model, it's settable somewhere in settings.

• I'm not sure whether the red lines are from your editing or from the code model. If the latter it looks like it's got itself lost all over the place.

• If I understand you rightly, you said the "cannot initialize ..." message only occurs if you have QVector<QCommandLineOption *> and not if you make that a QList. That line comes after the error message one and just has no relationship to it, so it's a mystery.

• As I wrote earlier, why don't you change over from QVector to QList anyway if that solves it, as that will be better going forward and makes no difference to you now?

[Khamza]

@JonB
Thanks for your response.

1. +
2. I use built-in model. Yes it's clang
3. I thought it's because of git.
4. +
5. So, i thought that QVector is more preferable than QList. Also i already used QVector in all other code.
   P.S. Why should i call explicitly QCommandLineParser in CommandLineParser? Isn't it called implicitly?