On 2019-10-26 11:43, Konrad Rosenbaum wrote:
Hi,
On 10/24/19 5:53 PM, Murphy, Sean wrote:
I'd like to be able to have QSettings write out my settings to an INI
file format, but I'd like to avoid writing it to an actual file,
instead just writing it to "something" in memory (for example, a
QString, QByteArray, QBuffer, etc.).
That's because QSettings is rather complex underneath - it handles
stuff like multiple instances accessing the same file at the same
time, hierarchies of settings-files (e.g. system level and user
level), etc. If you handed in a QIODevice then QSettings could not be
sure what the state of the underlying IO-Object is and whether it is
safe to access it.
So I if all the above is correct, and there is no way to write an INI
formatted string to memory, and given the fact that I really don't
want a file in the first place, I decided to look at writing the
settings out to a QTemporaryFile, then just reading that data back in
as a string, and then let the QTemporaryFile go out of scope and
clean itself up. But according to the following test code, QSettings
does not seem to play nicely with QTemporaryFile:
This is basically the way to go.
void MainWindow::writeSettings()
{
// comment/uncomment the *define* below to switch implementations
#define USE_QTEMPORARY_FILE
#ifdef USE_QTEMPORARY_FILE
// using a QTemporaryFile doesn't seem to work
QTemporaryFile tempFile;
bool ok = tempFile.open();
#else
// if instead you use a regular QFile, it works
QFile tempFile("tempFile.ini");
bool ok = tempFile.open(QIODevice::ReadWrite);
#endif
if(ok)
{
qDebug() << "Opened" << tempFile.fileName();
} else {
qDebug() << "Unable to open" << tempFile.fileName();
}
Call tempFile.fileName() before you call close()! (But close() before
you instantiate QSettings.)
tempFile.close();
QSettings settings(tempFile.fileName(), QSettings::IniFormat);
settings.setValue("string", "hello");
settings.setValue("int", 2);
settings.sync();
// using QTemporaryFile always produces an AccessError here,
Because QSettings has the file locked. Make sure settings goes out of
scope before you re-open the file.
Granted, it's complex with the locking code, but underneath it all you
have this hidden gem writeIniFile(), which takes a QIODevice and the map
(you know, the function with those hardwired [General] and [General%]
strings).
Suggestion: you have this nice extension/plugin call
QSettings::registerFormat(), which takes a readFunc and a writeFunc ptr.
If that writeIniFile() could be exposed as a public writeFunc ptr (yes
it has the same function signature) then you could have users bypass the
locking stuff, by requiring them to register a new format (say with the
extension "buffer" for a QBuffer) but allowing them to reuse the
existing writeIniFile() as their own writeFunc (and say a QBuffer as the
QIODevice).
That way you could access the streaming functionality of QSettings
without involving the file system.
Rgrds Henry
_______________________________________________
Interest mailing list
Interest@qt-project.org
https://lists.qt-project.org/listinfo/interest
