[Qt-interest] QFile::copy() fails on Windows Vista if the source is in resources (Was Re: QFile::remove() fails on Windows Vista)

[Yevgen Muntyan]

Hey,

I tried simple QFile::rename(), it works fine for regular files. My 
program copies a file from
resources and apparently that hits an unlucky code path.

DeleteFile fails because the file is held by someone else. I can't 
delete the file while the application
is sitting in debugger right before DeleteFile call. DeleteFile returns 
0, and GetLastError is 32.
Trying to delete file in cmd.exe I get "The process cannot access the 
file because it is being used
by another process." After I let the program run further (and after 
QFile::rename() fails), I can
delete the file without problems, with or without "\\?\" prefix. What I 
said earlier about the prefix
was wrong, I simply tried to delete the file while the program was stopped.

The following is a complete test case which reproduces my problem (you 
need to add a resource
file which includes some file, deltest.pro in this code):

#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QFile file(":/deltest.pro");
    if (file.copy("copycopy.txt"))
        QMessageBox::information(0, "yay!", "yay!");
    else
        QMessageBox::critical(0, "oops!", file.errorString());
    return 0;
}

It gives me "Cannot create copycopy.txt for output" (it's lying, the 
error message is overwritten inside
QFile::copy).

Best regards,
Yevgen

Constantin Makshin wrote:
> "\\?\" prefix is used to extend the maximum path length from 259 to ~32000  
> characters. Could you call DeleteFileW(L"\\?\<path>"), where <path> is the  
> absolute path to your temporary file with backslashes as path delimiters,  
> directly and see what it returns?
>
> On Mon, 22 Jun 2009 21:00:48 +0400, Yevgen Muntyan <muntyan at fastmail.fm>  
> wrote:
>   
>> Yevgen Muntyan wrote:
>>     
>>> Hey,
>>>
>>> I have a problem with QFile::rename: it fails when it tries to remove  
>>> the
>>> temporary file it uses, because DeleteFileW() fails inside
>>> QFSFileEngine::remove(). My code is roughly the following:
>>>
>>> QFile source(":/gap/ggap.g");
>>> source.copy("C:/Users/muntyan/AppData/Local/Temp/ggap-000025cb/ggap.g")
>>>
>>> The copy() call here fails.
>>> "C:/Users/muntyan/AppData/Local/Temp/ggap-000025cb" directory is created
>>> with QDir::mkdir(), and I do have permissions to delete files from it,  
>>> and I
>>> can delete files from it in explorer. The temporary files  
>>> qt_temp.XXXXXX are
>>> not read-only, so DeleteFile() isn't supposed to fail. But it does!
>>>
>>>       
>> I found out that Qt calls DeleteFile() on some funny long version of the
>> filename, namely it passes
>> the following string to DeleteFile:
>>
>> \\?\c:\Users\muntyan\AppData\Local\Temp\ggap-00002d22\qt_temp.Za5308
>>
>> it prepends \\?\ in QFSFileEnginePrivate::longFileName(). DeleteFile()
>> doesn't fail if I call it on
>> the filename without that prefix. Ideas?
>>
>> Thanks,
>> Yevgen
>>     
>
>