Qt cannot cannot create/write to C:\

Question

I am writing a Qt program (4.7 for windows 7 initially) that requires writing to the installed directory (C:\Program Files...). No files are being created when I try to write to a location that would be "protected" (program files, C:\ etc). However, QFile is not giving me any error code (error() is returning 0 which means it worked fine).

Here is a code snippit that I am using that is not working. I am closing the file its just much later in the program.

QApplication a(argc, argv);

// Setting plugin paths.
QStringList paths = QCoreApplication::libraryPaths();
paths.append(QCoreApplication::applicationDirPath());
QCoreApplication::setLibraryPaths(paths);



// Debug file.
QString path = QCoreApplication::applicationDirPath() + "/debug.dat";
//QFile debugFile(QCoreApplication::applicationDirPath() + "/debug.dat");
QFile debugFile("C:/debug.txt");
qDebug() << debugFile.error();
debugFile.setPermissions(QFile::WriteUser | QFile::WriteGroup | QFile::WriteOwner | QFile::WriteOther);
debugFile.open(QFile::WriteOnly);
QTextStream debugStream(&debugFile);

// Processing the arguments.
debugStream << QString("Processing Arguments\n");

Does anyone have any tips on how to solve this problem?

Thanks for the help,

Jec

Adding a manifest file is the route I choose to fix this problem.

Thanks for all of the help.

"However, QFile is not giving me any error code": You should check the return value of debugFile.open(). — Frank Osterfeld, Jan 09 '11 at 18:25

score 7 · Accepted Answer · answered Jan 09 '11 at 19:58

Have you checked whether the file isn't created in the VirtualStore for that user? Check the Event Viewer under Applications and Services Logs -> Microsoft -> Windows -> UacFileVirtualization -> Operational. If you see entries with event ID 5000, a FileCreateVirtualExclude event has occurred.

Check if the file didn't get created under %USERPROFILE%\AppData\Local\VirtualStore. If it did, you might need to embed a manifest requesting the required privileges (i.e., turning virtualization off.)

For more details, see New UAC Technologies for Windows Vista (scroll down and look for Virtualization.)

You were absolutely correct. My files were being stored in the virtual store (well most of them anyway. I had a subfolder that wasn't being stored virtually for some reason). I added the manifest so my program is now running virtually. Thanks. — jecjackal, Jan 10 '11 at 04:00

score 2 · Answer 2 · answered Jan 09 '11 at 18:04

2

You need to acquire sufficient user access rights (ie "Run as Administrator") to write to such folders in Windows Vista+. Either start the app as administrator, or ask for Administrator rights via a call to WinAPI.

answered Jan 09 '11 at 18:04

rubenvb

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AFAIK you can't request admin rights for an already running process but have to start another process to perform the operations requiring those permissions. – Frank Osterfeld Jan 09 '11 at 18:24

score 2 · Answer 3 · answered Jan 09 '11 at 22:45

2

QFile may be giving you an error code, but you've failed to check for it.

You should do something more like:

if (!debugFile.open(QFile::WriteOnly)) {
    qWarning() << "Failed to open" << debugFile.fileName() << "for write:" << debugFile.errorString();
}

You've checked the return value of QFile::error, but only before calling open - you need to check after the open attempt.

answered Jan 09 '11 at 22:45

rohanpm

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Wow, you were right. I was checking the error code before opening the file. Well thats what happens when I stay up late coding :). Thanks. – jecjackal Jan 10 '11 at 04:01

Qt cannot cannot create/write to C:\

3 Answers3

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