Re: [Boost-users] [Boost.UTF] Strange (failed) result on comparing floats

Subject: Re: [Boost-users] [Boost.UTF] Strange (failed) result on comparing floats
From: Olaf Peter (ope-devel_at_[hidden])
Date: 2010-03-31 14:19:14

Paul A. Bristow schrieb:
>> -----Original Message-----
>> From: boost-users-bounces_at_[hidden] [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Steven Watanabe
>> Sent: Wednesday, March 31, 2010 3:35 PM
>> To: boost-users_at_[hidden]
>> Subject: Re: [Boost-users] [Boost.UTF] Strange (failed) result on comparing floats
>>
>> AMDG
>>
>> Olaf Peter wrote:
>>> I'm checking some data of consistence using boost's unit test framework
>>> (1.42):
>>>
>>> BOOST_CHECK_CLOSE( *v[1].y.max, -43.0e-3,
>>>     std::numeric_limits<double>::epsilon() );
>>>
>>> which fails with:
>>>
>>> difference{1.6137e-14%} between *v[1].y.max{-0.043000000000000003} and
>>> -43.0e-3{-0.042999999999999997} exceeds 2.2204460492503131e-16%
>>>
>>> where v is a std::vector,y a struct and max a boost::optional<double>.
>>> The data where parsed by boost.spirit. This is the only failed test case
>>> from 16 parsed doubles. What's gone wrong here? Do I miss something?
>>>
>> epsilon is too small.  BOOST_CHECK_CLOSE treats the
>> argument as a percent, so there's an extra factor of 0.01, which
>> means that this comparison is effectively for equality.
> 
> Well spotted Steven.
> 
> BOOST_CHECK_CLOSE_FRACTION( *v[1].y.max, -43.0e-3, std::numeric_limits<double>::epsilon() );
> 
> is what you meant?

Yes, Thanks!

> Our esteemed and illustrious author of the invaluable Test library was begged not to use percents but ...

why this?

Olaf