Adam Lerer wrote:
a) not every binary floating number has en exact representation when rendered as decimal. True, but if max_digits10 digits is used, you can at least guarantee that the binary representation will deserialize as the same float. This is very helpful for common use cases of the serialization library
I understand that float serialization cannot be guaranteed to work correctly in all cases. That said, the precision used for float serialization is a choice, and some choices are better than others. It seems to me that the choice of max_digits10 (or even better, Paul's alternative formula to work around the VS bug) is superior to digits10+2.
It might also be helpful to note that lexical_cast uses exactly the formula that Paul recommends. In lcast_precision.hpp:
BOOST_STATIC_CONSTANT(unsigned long, precision_bin = 2UL + limits::digits * 30103UL / 100000UL );
Feel free to add a trac item for this Robert Ramey