QFile doesn't detect read-only files

Sucharek

Hello, I've came across a problem. I'm making a sorting system, and I'm checking if the file is read-only, so I can check, if the file got moved, or not, but it doesn't work.
I try to detect if the file exists (which it does), but QFile doesn't detect it.
Here's my code for it:

        qDebug() << "file:" << filename;
        QFile move(mainPath + filename);
        bool system = move.isWritable();
        if (system == false) {
            move.copy(mainPath + rPath + filename);
            QFile check(mainPath + rPath + filename); //path of the moved file
            if (check.exists()) { //here it detects, always false even if it does exist
                move.remove();
            } else {
                qDebug() << mainPath + rPath + filename;
                qDebug() << check.exists();
                QMessageBox error;
                error.setWindowTitle("Error!");
                error.setText("Warning! There was an unexpected error!\n"
                              "File has not been manipulated!\n"
                              "File path: " + mainPath + filename);
                error.exec();
            }
        } else {
            move.rename(mainPath + filename, mainPath + rPath + filename);
            qDebug() << "from: " + mainPath + filename;
            qDebug() << "to: " + mainPath + rPath + filename;
        }

mchinand

@Sucharek You may be having issues because your file is a .lnk file (shortcut) which I think is treated as a symbolic link, so keep that in mind when you are reading the documentation on various file manipulation methods. For copy(), the documentation says it copies the file that the .lnk file is referring to, not the .lnk file itself.

Christian Ehrlicher

What OS, Qt version and filesystem type do you use?

Sucharek

Hi @Christian-Ehrlicher, I'm on windows, my Qt version is 5.15.2 and my filesystem is NTFS

mchinand

@Sucharek said in QFile doesn't detect read-only files:

    bool system = move.isWritable();
    if (system == false) {
        move.copy(mainPath + rPath + filename);

You might want to check the return value on your copy command

        QFile check(mainPath + rPath + filename); //path of the moved file
        if (check.exists()) { //here it detects, always false even if it does exist
            move.remove();

This might be filesystem dependent, but I don't think you will be able to remove a file that you don't have write-access to (this is within the if-block when isWritable() is false).

Sucharek

Hi @mchinand, the return value of copying is true, and I can remove the file, even when it's unwritable (with QFile::remove()).

JonB

@Sucharek
You claim QFile::exists() returns false. What does QFileInfo have to say about the file?

Christian Ehrlicher

This is working fine for me on a NTFS file system with Qt5.15.2 (assuming a read-only file named 'tmp1.txt' is in D:\

int main(int argc, char** argv)
{
    QCoreApplication app(argc, argv);
    QString filename = "tmp1.txt";
    QString mainPath = "D:/";
    QString rPath = "subdir/";
    if (!QDir().mkpath(mainPath + rPath)) {
        qDebug() << "Could not create path " << mainPath + rPath;
    }
    QFile move(mainPath + filename);
    bool system = move.isWritable();
    if (system == false) {
        move.copy(mainPath + rPath + filename);
        QFile check(mainPath + rPath + filename); //path of the moved file
        if (check.exists()) {
            qDebug() << "Copied file at " << check.fileName() << "exists - removing";
            move.remove();
        }
        else {
            qDebug() << "Copied file at " << check.fileName() << "does not exist";
            qDebug() << mainPath + rPath + filename;
            qDebug() << check.exists();
        }
    }
    else {
        qDebug() << "File is writeable";
    }
    return 0;
}

mpergand

I don't know on Windows but on Mac since the file is not open for writing, isWritable() return false

   QFile file(path);
   QTLog(<<"is writable"<<file.isWritable())       
       if(file.open(QIODevice::WriteOnly))
           { 
           QTLog(<<"is writable"<<file.isWritable())  
            ...

is writable false
is writable true

mchinand

The documentation says QIODevice::isWritable() checks the OpenMode, so seems like your finding isn't specific to Mac and QIODevice::isWritable() is only useful for open files. QFileInfo::isWritable() is what is needed here.

mpergand

@mchinand said in QFile doesn't detect read-only files:
so seems like your finding isn't specific to Mac

Yes I know ;)
All the topic makes no sense because there is a confusion between the open state of a file (read/write) and the permissions for a file.

Sucharek

Hi, thanks for all the replies, but none of them seem to work.
@JonB QFileInfo returned false.
@Christian-Ehrlicher your method doesn't work for me. Prints:
Copied file at "C:/Users/username/Downloads/Other/Spotify.lnk" does not exist
But it actually does exist.

mchinand

@Sucharek You may be having issues because your file is a .lnk file (shortcut) which I think is treated as a symbolic link, so keep that in mind when you are reading the documentation on various file manipulation methods. For copy(), the documentation says it copies the file that the .lnk file is referring to, not the .lnk file itself.

Sucharek

Hi @mchinand, thank you for your answer.
I guess that explains my issue.
Thanks

JonB

@Sucharek said in QFile doesn't detect read-only files:

Copied file at "C:/Users/username/Downloads/Other/Spotify.lnk" does not exist

This is a .lnk file. You never mentioned this, even though it behaves differently from all other file types under Windows. Did you not think that relevant? The QFile etc. documentation tells you how it handles .lnk files --- effectively, it always tells you about the file pointed to by the .lnk file, not the .lnk file itself. So, for example, when you say QFile::exists() reports it as not existing, it is telling you about the file the .lnk points to. Did that exist?

@JonB QFileInfo returned false

You were supposed to look through the various QFileInfo::is...() methods, not just QFileInfo::exists(), to see what the attributes of the file are. For instance, QFileInfo::isShortcut() under Windows would have told you/us what is relevant here.