Match nested capture groups with quantifiers using QRegularExpression

Question

I'm trying to get with a QRegularExpression all attributes of an xml tag in the different captured groups. I use a regex matching the tags and I manage to get the capture groups containing the attribute value but with a quantifier, I get only the last one.

I use this regex :

<[a-z]+(?: [a-z]+=("[^"]*"))*>

And I would like to get "a" and "b" with this text :

<p a="a" b="b">

Here is the code:

const QString text { "<p a=\"a\" b=\"b\">" };
const QRegularExpression pattern { "<[a-z]+(?: [a-z]+=(\"[^\"]*\"))*>" };

QRegularExpressionMatchIterator it = pattern.globalMatch(text);
while (it.hasNext())
{
    const QRegularExpressionMatch match = it.next();

    qDebug() << "Match with" << match.lastCapturedIndex() + 1 << "captured groups";
    for (int i { 0 }; i <= match.lastCapturedIndex(); ++i)
        qDebug() << match.captured(i);
}

And the output :

Match with 2 captured groups
"<p a=\"a\" b=\"b\">"
"\"b\""

Is it possible to get multiple capture groups with the quantifier * or have I to iterate using QRegularExpressionMatchIterator with a specific regex on the string literals?

Why regex? See [a non-regex approach here](https://www.qtcentre.org/threads/31522-Qt-way-of-getting-parsing-style-attributes-from-html-tags-local-file-batch). An [SO thread](https://stackoverflow.com/questions/32082181/how-to-get-xml-attributes-with-this-syntax-using-qt-dom) here. A more generic: [How to parse an HTML file with QT?](https://stackoverflow.com/questions/49223317/how-to-parse-an-html-file-with-qt) — Wiktor Stribiżew, May 08 '19 at 11:45

Emma · Answer 1 · 2019-05-08T13:34:37.837

This expression might help you to simply capture those attributes and it is not bounded from left and right:

([A-z]+)(=\x22)([A-z]+)(\x22)

Graph

This graph shows how the expression would work and you can visualize other expressions in this link, if you wish to know:

If you would like to add additional boundaries to it, which you might want to do so, you can further extend it, maybe to something similar to:

(?:^<p )?([A-z]+)(=\x22)([A-z]+)(\x22)

Test for RegEx

const regex = /(?:^<p )?([A-z]+)(=\x22)([A-z]+)(\x22)/gm;
const str = `<p attributeA="foo" attributeB="bar" attributeC="baz" attributeD="qux"></p>`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

Thanks for your help. But here I still have to loop using the regex engine (QRegularExpressionMatchIterator) and we can't have all the attributes in the different capture groups of one match. Is that correct ? — Maluna34, May 08 '19 at 14:34

Match nested capture groups with quantifiers using QRegularExpression

1 Answers1

Graph

Test for RegEx