I have QString variable named "src", which holds a filename. Operation QFile::copy(src, target) works Ok, until target is "C:" or "C:/" (I have the problem in Windows 10). In this case the operation returns true, even though I do not see any files actually copied to C:/ (in fact, normally I cannot copy anything to C:/ without administrator rights). Moreover, when I debug, I see that it says it has copied to C:// (two slashes). Is it a Qt bug or do I miss something?
UPD: Copying, e.g., to C:/Users which also requires administrator rights fails, as it should (returns false). Qt version is 5.7.
UPD:
QString src = "C:/Stuff/somefile.pdf";
QString target = "C:/somefile.pdf";
if (QFile::copy(src, target)) qDebug() << "Copy successful";
else qDebug() << "Copy failed";
This code yields "Copy succeful", whereas neither do I have write access to C:/ nor actually file somefile.pdf appears there.
When your application does not have permissions for writing to some directories, the files are stored into the Windows Virtual Store located at C:\Users\%USERNAME%\AppData\Local\VirtualStore. So in fact your file is successfully saved (albeit the path is redirected), that is why QFile::copy() returns true.
This redirection is called UAC Virtualization, and it works for C:, C:\Program Files, C:\Windows and HKLM\Software.
I guess the most genuine way to avoid such problems is to stick to saving configuration data in the designated locations such as application data (which in the context of the Qt framework will also meet the terms of cross-platform code).