Paul A Bristow wrote:
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Robert Ramey Sent: 30 December 2007 16:53 To: boost@lists.boost.org Subject: Re: [boost] A question regarding serialization lib
I would expect that in your test text1.doc would be identical to text2.doc.
UNLESS you have have floats/double in your classes. In general, it cannot be guarenteed that there is a one-to-one correspondence between floatiing point values as represented by binary in ram to text numbers represented as decimal based text. So in this case I would expect text1.doc to not be identical to text2.doc.
The chances of this a very small 1 in 3 values of a very narrow range- and only MS is known to have this problem as the link below shows.
The following feedback item you submitted at Microsoft Connect has been updated:
Product/Technology - Visual Studio and .NET Framework Feedback ID - 98770 Feedback Title - Decimal digit string input to double may be 1 bit wrong.
The following fields or values changed:
Field Status changed from [Resolved] to [Closed]
To view these changes, click the following link, or paste the link into your web browser:
http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?Feedbac... (requires sign-in)
Amazingly (to me at least) this is a 'feature' and may not be fixed - despite it looking very much like a simple out-by-1 error.
What is most amusing is that under .Net there is actually a format specifier ('r') for converting a .Net String to and from a double which guarantees that the textual representation will stay exactly the same. Yet at the same time you are told in response to your report that "Round-tripping through all the machinery of input and output passes through various representations, and cannot be guaranteed to be identical to the original." However I did not see a way of guaranteeing this in native C++ under VC++.