Detecting PDF Printing on Mac - c++

Question

I use a QPrintDialog to initialize a QPrinter object like this:
QPrinter printer;
QPrintDialog dlg(&printer);
if (dlg.exec() == QDialog::Accepted)
{
/* Are we printing to PDF? */
}
On Windows, it's easy to detect if the output is going to a file or to a PDF writer. On a Mac, none of the same functions work:
if ((printer.outputFormat() == QPrinter::PdfFormat)
|| (!printer.outputFileName().isEmpty()))
{
qDebug("PDF mode");
}
Looking at a copy of qprintdialog_mac.mm online, in the function QPrintDialogPrivate::closeCarbonPrintPanel(), Qt attempts to detect if the output is redirected to a file. It stores the file name in a member of QMacPrintEnginePrivate. Somehow that name never makes its way to the QPrinter object. I'm not sure where the disconnect is.
So..... how can I tell if the print output is actually going to a file? I'm willing to get platform specific here if it's easy. I have zero Mac programming experience though.

Answer 1

This was a bug in Qt.
In Qt 5.3 the sample code provided will work because of the second condition, the call to QPrinter::outputFileName().

Answer 2

As of Qt 5.14, the outputFileName property of QPrinter is still null, even if "Save as PDF" was selected in the QPrintDialog.
However, when painting to the QPrinter object, the right thing is done.
if "Open with Preview" was selected, the painted contents will open
in preview.
if "Save as PDF" is selected, a file dialog will pop up
if "Send in Mail" is selected, the mail client will open with the PDF
attaced
etc.
Somehow, the QPrinter seems to store all the info from the dialog in an opaque way not accessible through public getters.
The correct way to support all the options from the mac print dialog seems to be:
QPrinter printer;
QPrintDialog dlg(&printer);
if (dlg.exec() == QDialog::Accepted)
{
QPainter painter;
painter.begin(&printer);
// do the painting
painter.end();
}
Unfortunately, it does not seem possible to extract the info out of the QPrinter object in case you like to implement your own printing logic.