What is the received/accepted method for storing real vals as int?

Question

Because converting between the various float flavors between MS Access (yes: yikes!), Java, and SQLite are so fraught with frustration, I want to store the reals as ints in SQLite. Is the preferred way of accomplishing this like so (pseudocode):

//real r = 36.57
string realAsStr = r.ToString();
// realAsStr is now "36.57"
// strip out the decimal point so that realAsStr becomes "3657"
int strAsInt = (integer)realAsStr; // strAsInt is 3657

...or like so:

int realAsInt = r * 100; // r * 100 is 3657.0[0]; realAsInt = 3657

...or like some other so?

Note: these vals stored as real types in MS Access are monetary values, stored as doubles.

Just remember if there is any decimals in your data and you put it in an int it will always truncate everything after the decimal. In case you have fractions of pennies you need to carry over. — CodeCamper, Apr 14 '14 at 16:12
At http://stackoverflow.com/questions/13467849/double-multiplied-by-100-and-then-cast-to-long-is-giving-wrong-value, there is a theoretical answer for the propeller-heads; for those who just want a practical solution, it appears to be: long l =Math.round(r*100); — B. Clay Shannon-B. Crow Raven, Apr 14 '14 at 16:22

score 1 · Accepted Answer · answered Apr 14 '14 at 16:47

1

Simply multiply the real value with 10^x where x is the number of relevant digits after comma.

Then round or truncate, and assign to int.

Example:

Asume 3 digits after comma is relevant for your application:

double doubleVal = 127.123;
int intVal = (int) doubleVal * 1E3; // 1E3 = 1* 10^3 = 1000.0;
// intVal now is 127123

When reading back simply divide by 10^x:

intVal = 127123; // from DB
double val = intVal / 1E3;

// val now 127.123;

answered Apr 14 '14 at 16:47

AlexWien

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Is this better than "Math.Round(Bla*100)? – B. Clay Shannon-B. Crow Raven Apr 14 '14 at 17:12
1

It is the same if you decide that 100 is sufficient. At least use a constant: double floatToIntFactor = 100.0; but 100 is of type int, 100.0 is safer in some situations. – AlexWien Apr 14 '14 at 17:29
Nebenbei bemerkt: vor acht Jahren besuchte ich deiner Stadt (Vienna). – B. Clay Shannon-B. Crow Raven Apr 14 '14 at 17:39
If I use int instead of long, I get, "error: incompatible types: possible lossy conversion from long to int" – B. Clay Shannon-B. Crow Raven Apr 14 '14 at 17:47
"possible lossy conversion from long to int" This is a warning, check if you have the cast to (int);: otherwise check your project setting, you might have treat warnings as errors enabled. Of course there is a possible loss, but this is wanted. – AlexWien Apr 14 '14 at 17:49
Wouldn't it be okay to just keep the data type as long? – B. Clay Shannon-B. Crow Raven Apr 14 '14 at 17:53
In this sort of situation you should always round() and not just truncate; it is far more likely to do what you want… – Donal Fellows Apr 14 '14 at 18:41
You have to decide whether round or truncate. This is one of the most complex things to decide whether to round or truncate. Especially to make that consistent with your whole tool chain. – AlexWien Apr 14 '14 at 18:50
@B.ClayShannon yes keep as long, but int needs less space. Your orignal question was how to convert real to int. – AlexWien Apr 14 '14 at 18:51

B. Clay Shannon-B. Crow Raven · Answer 2 · 2014-04-14T18:00:23.423

A few steps are necessary:

0) Change the data type of the class members in question to "long":

private long _cost;
private long _margin;
private long _listPrice;

1) When reading the values returned from the RESTful method (json), convert them from double to long:

Double cost = jsonObj.getDouble("cost");
Double margin = jsonObj.getDouble("margin");
Double listPrice = jsonObj.getDouble("listPrice");
long costAsLong = Math.round(cost*100);
long marginAsLong = Math.round(margin*100);
long listPriceAsLong = Math.round(listPrice*100);

DeliveryItem delItem = new DeliveryItem();
. . .
delItem.set_cost(costAsLong);
delItem.set_margin(marginAsLong);
delItem.set_listPrice(listPriceAsLong);
. . .

2) When displaying the values, display them as currency. IOW, what is stored as 3657 will display as $36.57

UPDATE

Updated based on AlexWien's answer to follow this pattern:

final double FLOAT_TO_INT_FACTOR = 100.0;
. . .
int costAsInt = (int) Math.round(cost*FLOAT_TO_INT_FACTOR);

(Class members have been changed from long to int)

What is the received/accepted method for storing real vals as int?

2 Answers2

UPDATE