//////////////////// DutchAuction ////////////////////DutchAuction::DutchAuction( const string newProductName ) : Auction( newProductName ){// cout << "max sum\n";// cin >> currentPrice;}/tmp/cck7buf8.o: In function `DutchAuction::DutchAuction(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':auction.cpp:(.text+0x4e9): undefined reference to `vtable for DutchAuction'/tmp/cck7buf8.o: In function `DutchAuction::DutchAuction(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':auction.cpp:(.text+0x551): undefined reference to `vtable for DutchAuction'collect2: ld returned 1 exit status