Re: [boost] lexical_cast issues under Tru64 Unix

From: Alexander Nasonov (alnsn_at_[hidden])
Date: 2006-10-13 15:08:39

Ralf W. Grosse-Kunstleve wrote:
> Alexander Nasonov wrote:
> > Does it mean that your std library doesn't define compile-time contants
> > in std::numeric_limits<T> ?
> 
> It does define std::numeric_limits<T>. Something more subtle must be wrong.
How it compiles this?

#include <ios>
#include <limits>
#include <boost/config.hpp>
#include <boost/integer_traits.hpp>
#include <boost/static_assert.hpp>

template<class T>
struct lcast_precision
{
    typedef std::numeric_limits<T> limits;

    BOOST_STATIC_CONSTANT(bool, use_default_precision =
            !limits::is_specialized || limits::is_exact
        );

    BOOST_STATIC_CONSTANT(bool, is_specialized_bin =
            !use_default_precision &&
            limits::radix == 2 && limits::digits > 0
        );

    BOOST_STATIC_CONSTANT(bool, is_specialized_dec =
            !use_default_precision &&
            limits::radix == 10 && limits::digits10 > 0
        );

    BOOST_STATIC_CONSTANT(std::streamsize, streamsize_max =
            boost::integer_traits<std::streamsize>::const_max
        );

    BOOST_STATIC_CONSTANT(unsigned int, precision_dec = limits::digits10 + 1U);

    BOOST_STATIC_ASSERT(!is_specialized_dec ||
            precision_dec <= streamsize_max + 0UL
        );

    BOOST_STATIC_CONSTANT(unsigned long, precision_bin =
            2UL + limits::digits * 30103UL / 100000UL
        );

    BOOST_STATIC_ASSERT(!is_specialized_bin ||
            limits::digits + 0UL < ULONG_MAX / 30103UL &&
            precision_bin > limits::digits10 + 0UL &&
            precision_bin <= streamsize_max + 0UL
        );

    BOOST_STATIC_CONSTANT(std::streamsize, value =
            is_specialized_bin ? precision_bin
                               : is_specialized_dec ? precision_dec : 6
        );
};

#include <iostream>

int main()
{
    std::cout << lcast_precision<float>::value << '\n';
    std::cout << lcast_precision<double>::value << '\n';
    //std::cout << lcast_precision<long double>::value << '\n';
}

-- 
Alexander Nasonov
Project Manager at Akmosoft ( http://www.akmosoft.com )
Blog: http://nasonov.blogspot.com
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