[Boost-users] [boost][numeric][conversion] boost::numeric_cast from integer to floating point (was Numeric Cast from integer to floating point)

Subject: [Boost-users] [boost][numeric][conversion] boost::numeric_cast from integer to floating point (was Numeric Cast from integer to floating point)
From: dariomt (dariomt_at_[hidden])
Date: 2014-09-10 04:39:49

Changed subject to see if it gets any attention...

 <dariomt <at> gmail.com> writes:
> 
> Hi,
> Quoting the docs for boost::numeric_cast: "There are several situations 
where conversions are unsafe: [...]Â Conversions from floating point types to 
integral types."
> 
> What about conversions from integral types to floating point types? E.g. 
from 64bit int to double.
> 
> The following example shows what I mean:
> 
> 
> #include <iostream>
> #include <cmath>
> #include <boost/numeric/conversion/cast.hpp>
> 
> int main()
> {
> Â  Â  const uint64_t i = 123445678911188878;
> Â  Â  std::cout << "i=" << i << std::endl;
> Â  Â Â 
> Â  Â  const double d = i;
> Â  Â  std::cout << "d=" Â  Â << std::fixed << d << std::endl;
> Â  Â  std::cout << "next=" << std::fixed << std::nextafter(d, 
 std::numeric_limits<double>::max() ) << std::endl;
> Â  Â  std::cout << "prev=" << std::fixed << std::nextafter(d, -
std::numeric_limits<double>::max()) << std::endl;
> Â  Â Â 
> Â  Â  // I'd expect the following cast to fail
> Â  Â  const double dd = boost::numeric_cast<double>(i);
> Â  Â  std::cout <<"dd=" << std::fixed << dd << std::endl;
> 
> Â  Â  return 0;
> }
> 
> 
> prints
> 
i=123445678911188878d=123445678911188880.000000next=123445678911188896.00000
0prev=123445678911188864.000000dd=123445678911188880.000000because that 
integer cannot be represented in double precisionIs there something in Boost 
to help here?Thanks in advance