Copy QStringList pointer to QStringList

Sikarjan

Hi,

how can I make a copy of a QStringList pointer that is not a new pointer? I am learning by doing and even if I've been reading about pointers I am still very unsure of the concept.

My goal is to dynamically update a QCompleter:

void CodeEditor::scanForVariables(){
    QStringList customCompList = new QStringList(completerList); // <- this is not working because completerList is a pointer. If it is not a pointer other parths of my code will not work

    QRegularExpression variableExpression = QRegularExpression("\\$[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*");
    QRegularExpressionMatchIterator matches = variableExpression.globalMatch(this->toPlainText());
    while (matches.hasNext()) {
        QRegularExpressionMatch match = matches.next();
        customCompList << match.captured();
    }

    QRegularExpression functionExpression = QRegularExpression("(?<=function )[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*(?=\\s*\\()");
    matches = functionExpression.globalMatch(this->toPlainText());
    while (matches.hasNext()) {
        QRegularExpressionMatch match = matches.next();
        customCompList << match.captured();
    }

    completerModel->setStringList(customCompList);
}

My problem is that setStringList does not allow pointers.

Thanks for any hints!

SGaist

Hi,

The first question is: why are you using pointers to QStringList ?

There's no need for that in your use case.

Sikarjan

Hi,

the completerList is used in different codeEditors. If it is not a pointer it will get copied over and over, right?

Best

J.Hilk

Hi,
first of, @SGaist is correct, no need to use pointers here.

But to answer your question, to copy your QStringlist you'll have to do either do a "deep copy" or copy each string and append it to your new list.

I would recommend the later one.

QStringList customCompList;
for( QString s : completerList)
       customCompList.append(s);

Sikarjan

Okay, this was quite a mess and a lot of try and error. Now I am not using pointers but the program crashes on the last line. "Segmentation error". The customCompList looks okay. The old and new values are there. Can I not do this:

QStringList customCompList = completerList;

And then append to it via <<? Will this mess up the list in the memory?

SGaist

If you pass your QStringList around using const references then no there won't be copies done and if you need really need to pass a pointer from time to time for a good reason, then just pass the address of your QStringList to that function.

Sikarjan

Hi,

I am new to the debugging tool. Here is what I get when I try to qDebug the list:

    for(QString s: customCompList)
        qDebug() << s;

		__for_begin	@0x28c1b8	QList<QString>::iterator
		__for_end	@0x28c1b4	QList<QString>::iterator
			i	@0x28c1b4	QList<QString>::Node
				v	0x123eb08 <vtable for QTextDocument+8>	void*
		__for_range	<2818 Elemente>	QStringList &
			[0]	"$GLOBALS"	QString
			[...]
			[2817]	"zlib_get_coding_type"	QString
		customCompList	<2819 Elemente>	QStringList

Why is the for range with 2818 elements one element short? The missing element is the one I added in the function.

SGaist

Where exactly are you calling that ?

Sikarjan

I replaced the setStringList with the for loop. The output is displayed in the Qt Debug window (the right one with all the variables).

Sikarjan

I got it. I needed to add

completerModel = new QStringListModel();

Prior setting the string list.