字符串转成NSDate类型，计算与当前时间的相差，年数，天数，时

NSString *dateStr=@"2013-08-13 20:28:40";//传入时间

//将传入时间转化成需要的格式

NSDateFormatter *format=[[NSDateFormatter alloc] init];

[format setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

NSDate *fromdate=[format dateFromString:dateStr];

NSTimeZone *fromzone = [NSTimeZone systemTimeZone];

NSInteger frominterval = [fromzone secondsFromGMTForDate: fromdate];

NSDate *fromDate = [fromdate  dateByAddingTimeInterval: frominterval];

NSLog(@"fromdate=%@",fromDate);

[format release];

//获取当前时间

NSDate *date = [NSDate date];

NSTimeZone *zone = [NSTimeZone systemTimeZone];

NSInteger interval = [zone secondsFromGMTForDate: date];

NSDate *localeDate = [date  dateByAddingTimeInterval: interval];

NSLog(@"enddate=%@",localeDate);

double intervalTime = [fromDate timeIntervalSinceReferenceDate] - [localeDate timeIntervalSinceReferenceDate];

long lTime = (long)intervalTime;

NSInteger iSeconds = lTime % 60;

NSInteger iMinutes = (lTime / 60) % 60;

NSInteger iHours = (lTime / 3600)$;

NSInteger iDays = lTime/60/60/24;

NSInteger iMonth = lTime/60/60/24/12;

NSInteger iYears = lTime/60/60/24/384;

NSLog(@"相差M年d月 或者 d日d时d分d秒", iYears,iMonth,iDays,iHours,iMinutes,iSeconds);