ios保留指定位数四舍五入

double temp = 0.3333333;
NSDecimalNumberHandler* roundingBehavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain scale:2 raiseOnExactness:NO raiseOnOverflow:NO raiseOnUnderflow:NO raiseOnDivideByZero:NO];
NSDecimalNumber* decimal = [[NSDecimalNumber alloc] initWithDouble:temp];
NSNumber* ratio = [decimal decimalNumberByRoundingAccordingToBehavior:roundingBehavior];