One cell in each row of a QTableWidget contains a combobox
for (each row in table ... ) {
QComboBox* combo = new QComboBox();
table->setCellWidget
No need for the signal mapper... When the combobox is created you can simply add two custom properties to it:
combo->setProperty("row", (int) nRow);
combo->setProperty("col", (int) nCol);
In the handler function you can get a pointer back to the sender of the signal (your combobox).
Now by asking for the properties you can have your row/col back:
int nRow = sender()->property("row").toInt();
int nCol = sender()->property("col").toInt();