Have you tried setting the QHeaderView
's Resize Mode?
QTableWidget* myTable = new QTableWidet;
QHeaderView* header = myTable->horizontalHeader();
header->setResizeMode(QHeaderView::Stretch);
Edit: As pointed out, in Qt 5:
QTableWidget* myTable = new QTableWidet;
QHeaderView* header = myTable->horizontalHeader();
header->setSectionResizeMode(QHeaderView::Stretch);