ok size?
 

So i just bought a 56 cm 05 langster on craigslist ,I am about 5'9,this should be a good fit right?

most likely. at least it will be close.

go to competitivecyclist.com they have a pretty good fit calculator
no one should size a frame off just their height and inseam

I would say that you are in the ball park but may want to go with a shorter stem depending on your body geometry / ride preferences

I'm 5'11" w/ 33" inseam. I ride a 54cm Langster and a 56cm road frame both with 120mm stems. The more aggressive saddle to bar height on the Langster made me choose the 54cm frame over the 56cm. The 56cm Langster felta bit stretched out for my preferences. Both bikes fit me like a glove.