I want to know if the QTableWidget column is being changed with the mouse. How can I emit a signal when any of the columns changes?
Column resizing is done horizontally QHeaderView. Enter it, calling QTableWidget::horizontalHeader() const, and the signal you are interested in QHeaderView::sectionResized(int logicalIndex, int oldSize, int newSize).
QHeaderView
QTableWidget::horizontalHeader() const
QHeaderView::sectionResized(int logicalIndex, int oldSize, int newSize)