Re: rounding problems

[Craig Ringer <craig@xxxxxxxxxxxxxxxxxxxxx>]

Justin wrote:

> No floating point is being used every variable is declared as numeric on 
> the Postgresql side and in the C++  which is the UI side everything is 
> double.

`double' in C++ refers to double precision floating point. `double' is 
subject to all the usual fun with rational decimals being irrational 
binary floats (and vice versa).

One of the reasons I chose Java for my current work is that it has a 
built-in decimal type (like `numeric') called BigDecimal . This makes 
working with exact quantities a lot easier as there's no conversion and 
rounding occurring each time data goes to/from the database.

Are there any particular decimal/numeric libraries people here like to 
use with C++ ? Or do you just use double precision floats and a good 
deal of caution?

I'd expect that using double would be OK so long as the scale of your 
numeric values never approaches the floating point precision limit of 
the double type. I'm far from sure about that, though, and it'd be handy 
to hear from people who're doing it. Personally I like to stick to 
numeric/decimal types.

--
Craig Ringer