iPhone - Store float in SQLite thru CoreData

Question

Hi everyone,

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

Answer 1

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.

Answer 2

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.