The general rule
§ 12-10-12(c): "If no action is taken on the complaint during the period of filing, the complaint shall be automatically expunged. No criminal record shall result."
One caveat in the same sentence: in a civil action for a tort, a plea of guilty or a finding of guilty remains admissible notwithstanding that the complaint was filed.
How long is a filing?
Not necessarily a year, though a year is common. § 12-10-12(a) leaves the length to the court's discretion, providing only that "in no event shall it be longer than the maximum jail sentence allowed by law" for the offense.
The conditions matter too. § 12-10-12(b) requires that during the filing period you keep the peace, be of good behavior, and have paid all outstanding court-imposed fees, fines, costs, assessments and other monetary obligations, unless reduced or waived by order of the court. A violation can bring the case back.
Domestic violence filings run on three years
This is the exception that catches people. § 12-1-12.1(c) requires the court to retain the records of a domestic violence filing for three years from the date of filing, and provides that they "shall not be expunged or sealed" during that period.
§ 12-10-12(d) then completes the picture: if for three years after the filing you are not charged with another crime involving domestic violence — or if charged, you are acquitted or it is dismissed — all records relating to the filed complaint are expunged without the requirement of filing a motion.
So a DV filing does clear automatically. It just takes three years rather than the filing period.
Which cases can be filed at all
§ 12-10-12(a) permits a judge to place on file any complaint in a criminal case other than a complaint for a felony, a complaint against a person who has been convicted of a felony, or a private complaint.