How to create a new QDir from an existing QDir + a subfolder?

[EchoReaper]

I have an existing QDir. I want a QDir for a folder inside. E.g.

void someMethod(QDir input) {
    QDir folderInInput = input.path() + "/SubfolderName";

    doStuff(folderInInput);
    ...
}

Normally, scripting languages will you allow to do something like QDir folderInput = input / "SubfolderName", but Qt doesn't. I could just use what I have above, but I'm not a fan of it because it hardcodes the slash. I could do input.path() + QDir::separator() + "SubfolderName", but that's too verbose. Does Qt have a more desirable way to index a subfolder of an existing QDir?

[J.Hilk]

Hi @EchoReaper and welcome

I'm not entirely sure what you try to do here, as doStuff seems to be a local function, but QDir offers a change directory function
cdUp to go one directory up and
cd(folderName) to change to a sub directory

If that is what you're looking for?

[EchoReaper]

cd kind of does what I want, but I want to create a new QDir rather than modifying an existing one. cd doesn't really make sense because of the variable names e.g.

QDir getDownloads(QDir userProfile) {
    userProfile.cd("Downloads");

    return userProfile;
}

We say we're returning userProfile, but we're not actually. We've changed the QDir to something else. I could clone the QDir and then change that, but that wouldn't be so elegant either. Preferred:

QDir getDownloads(QDir userProfile) {
    QDir downloads = userProfile.subfolder("Downloads");

    maybeDoStuffWithQDirIfThisIsNotSuchASimpleMethod(downloads);

    return downloads;
}

[J.Hilk]

@EchoReaper
Well no, there is no function in the QDir class that returns a new dir, at least not in the way you want it.

You could use the copy constructor?

Dir newDir(oldDir).cd("Downloads");

[EchoReaper]

I guess that will do. Thanks!

[JonB]

@EchoReaper said in How to create a new QDir from an existing QDir + a subfolder?:

Normally, scripting languages will you allow to do something like QDir folderInput = input / "SubfolderName", but Qt doesn't. I could just use what I have above, but I'm not a fan of it because it hardcodes the slash. I could do input.path() + QDir::separator() + "SubfolderName", but that's too verbose. Does Qt have a more desirable way to index a subfolder of an existing QDir?

I would say the "correct" Qt way of producing the path to a sub-folder, without using / or QDir::separator() the way you have (which isn't great if your starting directory ends with a /, like / or C:/, e.g. when QDir::isRoot() == true), is to use https://doc.qt.io/qt-5/qfileinfo.html#setFile-2, void QFileInfo::setFile(const QDir &dir, const QString &file).

You/Qt don't know whether the sub-item is a file or directory, that's why it's a QFileInfo method rather than a QDir one. You can then, say, feed QFileInfo::absoluteFilePath() to a new QDir() if you want to access it as a directory.

If you actually wish to create the sub-directory you could use https://doc.qt.io/qt-5/qdir.html#mkdir or https://doc.qt.io/qt-5/qdir.html#mkpath.