Qt QDockWidget adds extra margin space - c++

Question

I have a QDockWidget where both the contents and size of the dock should be the same. I currently am encountering an issue where although the size of the dock is valid; the parent central widget create a 4 pixel gap on the right which I cannot seem to shrink when resizing the mainwindow. Here's a screenshot:
This is the code that I use to force the dock to a specific size; which works fine and makes the dock the correct size. (it also contains a frame which should be the same size as the dock):
ui->dockFrame->resize(w, h);
ui->dock->setFixedSize(w, h);
I have also tried using layout()->setContentsMargins(0,0,0,0); for both the mainwindow and central widget to no avail.
Does anyone have an idea on where these extra pixels may be coming from, and how to resolve this issue? Thank you in advance.

Answer 1

The gap has very little to do with the QDockWidget. It's a property of QMainWindow - it's a movable separator between dock widgets, or between dock widget and a central widget.
You can get rid of it for example with the style sheet:
QMainWindow::separator
{
width: 0px; /* when vertical */
height: 0px; /* when horizontal */
}
in your C++ code:
mainwindow->setStyleSheet("QMainWindow::separator{ width: 0px; height: 0px; }");