DoubleValue doubleValue1; doubleValue1.m_value = -0.0070850229047457131; SaveDoubleValue(doubleValue1, "DoubleValue.xml");
DoubleValue doubleValue2; LoadDoubleValue(doubleValue2, "DoubleValue.xml"); //but from file is read -0.007085022904745714 assert(doubleValue1.m_value==doubleValue2.m_value);
That value would require between 50 and 60 bits of precision, provided its representation is actually possible in a binary floating point number. Typical double-precision floating point numbers have a fraction of 52 bits, so the changes you are reporting are actually to be expected.
I don't believe that's true: ideally the two values should have the same binary representation. In this case the relative difference between the two values is 1.6e-17 or about 1eps: so my guess is they differ in the last significant bit - that's not a double rounding issue, or shouldn't be. However, I suspect this to be an MSVC issue - there are some numbers that MSVC's IOStreams library can't "round trip serialize" - Robert does Boost.Serialization rely on iostreams internally in this case? I'm cc'ing Paul Bristow on this one, because I know he investigated this issue a while back. HTH, John.