Re: [Boost-users] boost serialization stream error question

OvermindDL1 wrote:

On Sun, Jan 31, 2010 at 6:11 PM, Robert Ramey wrote:

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OvermindDL1 wrote:

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On Sun, Jan 31, 2010 at 10:34 AM, Robert Ramey wrote:

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The problem is caused by double values less than DBL_MIN. Apparently, streaming such values in causes the input stream fail_bit to be set, which causes the serialization lib to throw an exception.

The standard stream library writes out NaN values as text, but cannot read them.

It shows up in various places besides the serialization library - e.g. lexical_cast.

Work has been done on this. I believe that there is code in vault which deals with this.

Why not just memcpy the double into the stream? (or bitcast it to long long or so?)

text and xml archives are meant to be portable. This would conflict with that requirement. Then there is the fact that putting binary data into the text stream might create some conflicts depending on the characterset etc. In general, one cannot put binary data into a text stream and be able to count on getting it back.

So here are a couple of options in order of my personal preference.

a) Just avoid saving and restoring NaN's. They just waste space in the archive anyway. There a number ways to do this. b) find the fixup for floating point stream in either the vault and/or sand box and install that. b) wrap the double in a binary_wrapper and serialize that. This would also break portability.

What about for text archives print/read it out in the completely portable C99 Hex floating point constant? It encodes all possible floating point values with no loss (including NaNs and such). It is basically just a hex representation of the memory, see the C99 hex floating point standard for how it works.

This is the first I've heard of this. I couldn't find any documentation on it either. I know some people have been working on addressing this and it has been found to be non-trivial. In any case, it's not something that would be in the serialization library but rather in the standard stream or some extension of it. I am surprised to hear about something like this in C99 which hasn't been included in standard stream C++ library. Makes me think I'm missing something here. Robert Ramey

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