I don't think we're talking about P&O or Cunard on this Carnival board, slacks and dress shirts are fine for Carnival. The ladies in my family with be in cocktail dresses and the men slacks, long sleeved shirt and tie (no jacket - oh my!!!!) and we will not be going against the dress code, nor would we if the men didn't wear ties and the ladies didn't wear dresses - as long as we weren't in shorts, T-shirts, bathing suits or jeans, we would be adhering to Carnival's dress code.
This is Carnival's dress code for "elegant" night:
Cruise Elegant Dining Dress Code: Gentlemen - Dress slacks, dress shirts. We also suggest a sport coat. If you wish to wear suits and ties or tuxedos, by all means we invite you to do so. Ladies - Cocktail dresses, pantsuits, elegant skirts and blouses; if you‘d like to show off your evening gowns, that's great too!
Not permitted in the dining room during the Cruise Elegant dinner for ladies and gentlemen: shorts, gym shorts, T-shirts, beach flip-flops, bathing suit attire, jeans, cut-off jeans, sleeveless shirts for men, sportswear, and baseball hats.