We have a server on windows, but it has a network drive which is actually on a linux server. The Program has to delete a file at the same location with the same name (signals), it works ok when those files are on local drive, but when running on the network drive, it will sometime not delete the file, and even worse, the functions will return that everything went ok(meaning the file is deleted). I tried with remove, _unlink, DeleteFileA , the problem still persists,sometime completely at random it won't be deleted and it will stay like this.
The code is really simple:
bool File::Delete()
{
if(isFile() && exist())
{
return DeleteFileA(filename.c_str()) != 0 ? true : false;
}
else
return false;
}
This will always return true even if the file is not removed, if for example it would not have permission it should fail(and fail each time, not at random), could someone give me an idea ? I ran out of options :(
Edit:
Thanks to #ExcessPhase, it seems like moveFile actually detects an error, so renaming before deleting can detect a problem "ERROR_FILE_NOT_FOUND".
Other things : This random problem can only happen when the files are created from linux server. If I create them from windows, they will always be deleted. Even more: If I have a file that the program cannot delete, and I create another file next to it from Windows, the program will detect and delete the one it could not delete before.
Edit2: Closer to answer: filename test and TEST in linux is different, while in Windows it's the same. The problem seems to appear at random when the case don't match. But I'm not sure since it's so random.
I believe the problem is with Samba service on Linux, which implements the SMB protocol for Windows. DeleteFile function just requests the SMB server (Server service on Windows) to delete a file. The success is returned by Samba.
Maybe you should try something more higher level like boost file system, or std::experimental::filesystem::remove
Related
(Note that this is not primarily a Qt question)
It seems to me that the return value of QFile::exists() is sometimes incorrect.
Consider the following two unit-test-like snippets (each of which I have executed a few thousand times in a loop)
// create file
QFile file("test.tmp");
QVERIFY(file.open(QIODevice::WriteOnly));
QVERIFY(file.write("some data") != -1);
file.close();
// delete file
QVERIFY(file.remove());
// assert file is gone
QVERIFY(!file.exists()); // <-- 5..10 % chance of failure
and
// create file
QFile file("test.tmp");
QVERIFY(file.open(QIODevice::WriteOnly));
QVERIFY(file.write("some data") != -1);
file.close();
// delete file
QVERIFY(file.remove());
// retry until file is gone (or until timeout)
for (auto i = 0; i < 10; i++)
{
if (!file.exists()) // <-- note that only the check is retried, not the actual delete
return;
QThread::yieldCurrentThread();
}
QFAIL("file is still reported as existing"); // <-- never reached in my tests
The first unit test fails about 8 out of 100 times. Always on the last line of code (indicating that the file still exists). The second unit test never fails.
This behavior was observed on a Windows 10 system using NTFS (with Qt 5.2.1). It could not be reproduced using ubuntu 16.04 LTS using ext4 on a VM (with Qt 5.8.0)
Not sure if this helps:
Process Monitor (when it succeeds)
Process Monitor (when it fails)
So my questions are:
what is happening?
what are implications that I might be interested in?
update:
For clarification: I am hoping for an answer like "this is caused by the NTFS feature 'bills-fancy-caching-magic'". From there I would like to find out, whether Qt does look over this feature intentionally.
According to the Windows API documentation, it is defined behaviour:
The DeleteFile function marks a file for deletion on close. Therefore, the file deletion does not occur until the last handle to the file is closed. Subsequent calls to CreateFile to open the file fail with ERROR_ACCESS_DENIED.
It seems to be a property of the Windows kernel and therefore not to be limited to NTFS.
The behaviour seems to be unpredictable, as other services (think virus scanners) might open the file in question.
Say I have an application I write, that relies for some task on an externat app (lets call it "tool") that is installed on my machine. In my program, I call it with system( "tool myarguments" ); , works fine.
Now, I want to distribute my app. Of course, the end-user might not have "tool" installed on his machine, so I would like my app to check this, and printout a message for the user. So my question is:
Is there a portable way to check for the existence of an app on the machine? (assuming we know its name and it is accessible through the machine's shell).
Additional information: First idea was to check the existence of the binary file, but:
This is platform dependent,
depending on how it has been installed (build from sources, installed through package,...), it might not always be in the same place, although it can be accessed through local path.
My first opinion on this question is "No", but maybe somebody has an idea ?
Reference: system()
Related: stackoverflow.com/questions/7045879
If you use the Qt toolkit, QProcess may help you.
Edit: and look for QProcess::error() return value: if it is QProcess::FailedToStart , then either it is not installed, or you have insufficient permissions.
If running the tool without argument has no side-effect, and is expected to return an exit code of 0, you can use system("tool") to check tool's existence.
You can check whether the command has been found by checking system's return value like this:
int ret = system("tool");
if (ret != 0) {
std::cout << "tool is not here, move along\n";
}
It is portable in the sense that system is expected to return 0 if all goes well and the command return status is 0 too.
For example, on Linux, running system("non_existing_command") returns 0x7F00 (same type of value as returned by wait()).
On Windows, it returns 1 instead.
I’m using the following code to delete an empty folder on Linux:
bool removeFolder (const QString& path)
{
QDir dir(path);
assert(dir.exists());
return dir.rmdir(".");
}
For some reason it sometimes returns false (for specific folders, but those folders don’t seem to be wrong in any way). If I subsequently use ::rmdir from <unistd.h> to remove the same folder, it succeeds.
How can I tell why QDir::rmdir is failing?
This never happened on Windows so far, QDir::rmdir just works.
Confirming: works on windown, fails on linux.
Reading the "rmdir" doc in <unistd>, here https://pubs.opengroup.org/onlinepubs/007904875/functions/rmdir.html, it says there that "If the path argument refers to a path whose final component is either dot or dot-dot, rmdir() shall fail." So what's probably happening is that QDir::rmdir() is calling the unistd rmdir() function in linux, and this one fails with ".".
I tried to just use the full absolute path ( QDir::rmdir(absolutePath) ) and it worked; however, i see basically no point in using QDir::rmdir() over unistd's rmdir(), so i''ll stick w/ the unistd rmdir() from now on.
note: QDir::removeRecursively() is a different story: it seems to work okay, and it's way more convenient than going through opendir() and then successive readdir()'s (or the nftw(...FTW_DEPTH...) thingie).
I had the same problem but on Windows, I could not delete an empty directory with QDir().rmdir(path);. This happened on some older hard drive so may be the ancient file system was to blame. But I found a hack:
QFile(path).setPermissions(QFile::WriteOther); // this works even for dirs
bool success = QDir().rmdir(path);
Of course, you should revert the permissions back to original values if the deletion was unsuccessful anyway, but that's a different story.
Try to use this one:
dir.rmdir(dir.absolutePath())
Good Day,
I have searched the Internet tirelessly trying to find an example of how to start Windows Speech Training from with in my VB.Net Speech Recognition Application.
I have found a couple examples, which I can not get working to save my life.
One such example is on the Visual Studios Fourms:
HERE
this particular example users the "Process.Start" call to try and start the Speech Training Session. However this does not work for me. Here is the exmaple from that thread:
Process.Start("rundll32.exe", "C:\Windows\system32\speech\speechux\SpeechUX.dll, RunWizard UserTraining")
What happens is I get and error that says:
There was a problem starting
C:\Windows\system32\speech\speechux\SpeechUX.dll
The specified module could not be found
So I tried creating a shortcut (.lnk) file and thought I could access the DLL this way. My short cut kind of does the same thing. In the short cut I call the "rundll32.exe" with parameters:
C:\Windows\System32\rundll32.exe "C:\Windows\system32\speech\speechux\SpeechUX.dll" RunWizard UserTraining
Then in my VB.Net application I use the "Process.Start" and try to run the shortcut.
This also gives me the same error. However the shortcut itself will start the SPeech Training session. Weird?!?
So, I then took it one step further, to see if it has something to do with my VB.Net Application and the "Process.Start" Call.
I created a VBScript, and using "Wscript.Shell" I point to the Shortcut.
Running the VBScript calls the Shortcut and low and behold the Speech Training starts!
Great! But...
when I try to run the VBscript from my VB.net Application, I get that error again.
What the heck is going on here?
Your problem likely is that your program is compiled as 32-bit and your OS is 64-bit, and thus, when you try to access "C:\Windows\System32\Speech\SpeechUX\SpeechUX.dll" from your program, you're really accessing "C:\Windows\SysWOW64\Speech\SpeechUX\SpeechUX.dll" which, as rundll32.exe is reporting doesn't exist.
Compile your program as 64-bit instead or try the pseudo directory %SystemRoot%\sysnative.
Also, instead of rundll32.exe, you may want to just run SpeechUXWiz.exe with an argument.
Eg.
private Process StartSpeechMicrophoneTraining()
{
Process process = new Process();
process.StartInfo.FileName = System.IO.Path.Combine(Environment.SystemDirectory, "speech\\speechux\\SpeechUXWiz.exe");
process.StartInfo.Arguments = "MicTraining";
process.Start();
return process;
}
private Process StartSpeechUserTraining()
{
Process process = new Process();
process.StartInfo.FileName = System.IO.Path.Combine(Environment.SystemDirectory, "speech\\speechux\\SpeechUXWiz.exe");
process.StartInfo.Arguments = "UserTraining";
process.Start();
return process;
}
Hope that helps.
Read more about Windows 32-bit on Windows 64-bit at http://en.wikipedia.org/wiki/WoW64
or your problem specifically at http://en.wikipedia.org/wiki/WoW64#Registry_and_file_system
If you are using a 64bit OS and want to access system32 folder you must use the directory alias name, which is "sysnative".
"C:\windows\sysnative" will allow you access to system32 folder and all it's contents.
Honestly, who decided this at Microsoft is just silly!!
I'am trying to watch a directory and notify for file changing(creation), I'am using a virtual machine (VirtualBox) on windows 7 and Ubuntu 12.04 as the guest, when a file was added to my watched folder I test the existence of this file to get its size and manipulate it later, the problem is: sometimes it return 0 as size although the file exists and have a non zero size, here is my code:
void Watcher::OnFileChanged (char* FileBaseName)
{
QDir watchDir(RootToWatch);
QString fileN="";
fileN=QString::fromLocal8Bit(FileBaseName);
QFileInfo file(RootToWatch+"/"+fileN);
qDebug()<<"Watcher::OnFileChanged "<<fileN;
try
{
if(file.exists())
{
qDebug()<<"FileWatcher::OnFileChanged "<<fileN<<"exists";
qDebug()<<"OnFileChanged:fileName "<<file.fileName()
<<"\nOnFileChanged File().size"<<QFile(fileN).size()
<<"\nOnFileChanged QFileInfo Size:"<<file.size();
....
}
}
}
should I wait for laps of time to get the real size (if yes how match and how test if the file is ready to be read) or do I missed some thing.
Any help will be appreciated.
This does sound like a typical case of "watcher goes off before the file is finally written" - which would be perfectly expected behaviour really, as all you can say is "tell me if this file has changed" - getting size zero is definitely a change - whether it previously existed or is just coming into existance, it's a change from the previous state.
My approach in this case would be to set the watch again, and see if the file has "grown" next time around.