How to position an added widget to a layout based on another widget in the same layout?

In my GUI, I would like to add a QComboBox to a verticalLayout programmatically based on a a signal triggered by specific action. The following code works fine and the widget is added:

QComboBox* userOptions = new QComboBox();
ui->verticalLayout_13->addWidget(userOptions);

However, this way the widget is always added to the end of the layout.

My question is: how to position the added QComboBox to the verticalLayout in alignment to another widget in the same layout ? (i.e.: above the "Go" push button for example)

Solution

There doesn't seem to be a way to explicitly insert an item in a layout where you want it to be.

You have a few choices to achieve that the "hard" way:

use QLayout::takeAt(int index) to take all items after the index you want to insert at, insert your item, then insert back the taken items.
create a placeholder widget which you can use to reserve an index in the layout, then you don't insert the item in the layout, but in a layout nested inside the placeholder widget. Without an item, the placeholder widget takes no space, and expands to accommodate whatever is put into it.
implement your own QLayout subclass which supports inserting at a specific index. There are several functions you will have to implement.

EDIT: An omission on my end, as Kuba Ober noted, most of the concrete layout implementations support inserting at a specific index, for example QBoxLayout derived have insert methods which pass an index as a parameter.