Riodejainero, is safe place in night...?

I V SEEN gang shooting vs police in the city.

This depends on many factors: where you goes, how you acts, what you wear, etc.
Don't look as a tourist and you will not call the attention. Look like a brazilian wearing the same clothes and act as a brazilian.
But it doesn't means that you will be safety for being considered a non-tourist. Brazilian thieves can't to depend on tourist's money to survive in their "business". So, brazilians are the main victims, of course.
Thieves will not cut your fingers, but, the general rules are: observe the brazilians and try to act in same way, and, keep on alert around.

As in most parts of the world, most gang violence is between gangs, between gangs and the cops, and/or restricted to certain neighborhoods. If you stay on the beaten track, you should be OK. Keep your eyes open in popular tourist areas (e.g. Copacabana, Ipanema) where people who look obviously foreign can sometimes be targets for petty theft.

Yeah if you hang out only in the chick areas such as Leblon, Ipanema, Arpoador etc...

http://www.abadboy.com/amateur/0703/676/...

Do not travel alone. When there, I was was warned that gangs of roving youths will "cut off your fingers to get the gold and jewelry". I was also advised to stay in the areas mentioned by others in their answers and not to wander off the beaten track. It is best not to carry a lot of cash or openly show jewelry. When leaving your hotel beware of hawkers that throw things to you - once you catch them, you have possession and they will hassle you for money for the item you just "bought".

Generally it is safe, but be cautious.