iPhone - Store float in SQLite thru CoreData

Question

I store a float number in my SQLite (through core data) like this:

unit.conversion = [NSNumber numberWithFloat:0.001];

When I look at the SQLite database the value is 0.0010000000474974513

unit.conversion is an optional float in my datamodel...

What's wrong with that?

Thanks

score 5 · Answer 1 · answered Sep 21 '10 at 22:45

5

Floating point numbers are not (always) exact representations - they are approximations.

See What Every Computer Scientist Should Know About Floating-Point Arithmetic for the background.

answered Sep 21 '10 at 22:45

martin clayton

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Thanks for the explanation but I need also a solution – ncohen Sep 21 '10 at 22:56
0.001 and the value you have in the database are, for most purposes, the same thing, as the above link probably explains. What exactly would you expect as a solution? – mrueg Sep 21 '10 at 23:01
the problem is that when I ll do some multiplications, I ll get float numbers with strange values... – ncohen Sep 21 '10 at 23:12
But you probably won't; you're going to be rounding for display, right? – Wevah Sep 22 '10 at 02:07

score 1 · Accepted Answer · edited May 23 '17 at 12:01

Given the fact that what you are seeing is correct (as already answered) and you are not happy with this: You can use NSDecimalNumber. A quick google search provided:

A Cocoa is my girlfriend post (this might fit your situation exactly)
A cocoa with love post
A tutorial about the different cocoa number containers
A stackoverflow answer

NSDecimalNumber allows you to do decimal arithmetic like how a financial institution would like you to do math. Warning: it is a little obnoxious to work with since all math operators are messages.

iPhone - Store float in SQLite thru CoreData

2 Answers2