The 3 main options are casual; smart and formal this covers most cruises and smart for gents is jacket/trousers and for ladies dress. The formal options can be tuxedo, although less and less lately; dinner jacket or suit and long dress or dress for the ladies casual is fairly obvious but shorts are normally not a good idea for the main restuarant.
Oops sorry, Seven seas Mariner
I quote from their web-site: "Shipboard attire ranges from Country Club casual to informal to formal. Country Club casual (resort-style attire) is appropriate for daytime on board or ashore. Shorts are not appropriate after 6 p.m. in any of the public rooms or lounges. Guests are asked not to wear bathing suits in the restaurants and lounges at any time. Evening attire can be Country Club casual, informal (sport coat and tie recommended), or formal (black tie optional). Evening dress codes begins at 6 p.m." There is a great deal of interesting and important information on the web-site and in the brochure, could be advantageous to read it....regards....Nei.