On Thu, 3 Aug 2006 12:29:34 +0100, "Paul A Bristow" <pbristow@hetp.u-net.com> wrote:
| >No - I meant 'stringizing' | | Ok. It seems to me we need something along these lines (off | the top of my head): | | #include "boost/limits.hpp" | | #define BOOST_is_ieee754(t) \ | typedef char required [ \ | std::numeric_limits<t>::is_iec559? 1 : -1 \ | ] /**/
This was important; see below.
This seems overcomplicated to me.
Uh? Ok, I started with the idea to not use numeric_limits<>, then used it :-) But I typed directly in the newsreader window so I'm forgiven (by myself :-P)
the guaranteed 'minimum' digits are already defined by numeric_limits<>::digits10() (for float 6)
Ok.
and the next version of C++ will provide numeric_limits<>::max_digits10() (for float 9)
I know. One point I'm not sure about, though: is it the intent for it to be defined (and != 0) for non IEEE 754 implementations too?
so all we need to do is to use the
stream.precision(2 + std::numeric_limits<Source>::digits * 301/1000);
Does that work for non IEEE 754 floating points too? I guess not. And in that case we have to check. There were two other points addresses by my code: single templates (or metafunctions) are largely preferable to the single monolithic numeric_limits (especially in boost, where including "boost/limits" will likely bring the world into your translation unit). That's, I guess, the position of most boosters. Secondly, static const data members of integral types (see also core issue 454) easily lead to ODR violations, with no diagnostic required. I'm eagerly waiting for strongly typed enums to solve that problem. The issue is: you can inadvertently bind the expression to a reference, for instance by using a vector<>::push_back, and nobody will provide a definition for you. Enums do not have such lvalue complications. I'd like that the declaration of static const ints members be made a definition (I believe modern linkers can manage that) but who knows... will that ever happen? (Probably obvious answer here) -- [ Gennaro Prota, C++ developer for hire ]