где ты это нашол ?
вот описание из моего Асистента
void QHeaderView::setResizeMode ( int logicalIndex, ResizeMode mode )
This is an overloaded function.
Sets the constraints on how the section specified by logicalIndex in the header can be resized to those described by the given mode. The logical index should exist at the time this function is called.
Note: This setting will be ignored for the last section if the stretchLastSection property is set to true. This is the default for the horizontal headers provided by QTreeView.