I used to go to loads of black tie events with OH when he was working and honestly anything goes! But usually if it's a dinner rather than a dinner/dance or ball I think a long dress is not going to be the norm. But it does depend on the function and where it's held.
Wear whatever you feel comfortable in, lots of pretty accessories and a shrug or wrap as air conditioning can be fierce.
Also don't think you have to wear black -at so many 'do's' most of the ladies wear black and shouldn't! It's very aging and draining - unless you know it suits you choose something more flattering to your colouring. And strapless is usually not good either unless you have very toned arms!
have a great evening!