"Pretty" lexical_cast

Hello!

I want to create a "pretty" lexical_cast, that formats numbers by rounding
them slightly. For example, the number 68.61893 is converted to
68.61893000000001 by lexical_cast to string. Likewise, the number 72.947251
is converted to 72.94725099999999. Is there a way to add or subtract a
small value before conversion, to get what I want? Here's my (failed)
attempt:

#include <boost/lexical_cast.hpp>
#include <limits>

using namespace boost;
using namespace std;

template<class T>
T pretty_lexical_cast(double x)
{
   T s = lexical_cast<T>(x);

   // I'm not sure what value to add/subtract here

   T s_p = lexical_cast<T>(x + numeric_limits<double>::epsilon());
   T s_m = lexical_cast<T>(x - numeric_limits<double>::epsilon());

   // return string with smallest number of characters
   if( s.size() < s_p.size() )
   {
      if( s.size() < s_m.size() )
         return s;
      else
         return s_m;
   }
   else if( s_p.size() < s_m.size() )
      return s_p;
   else
      return s_m;
}

int main()
{
   {
      double x = 72.947251;
      string s = pretty_lexical_cast<string>(x);
   }
   {
      double x = 68.61893;
      string s = pretty_lexical_cast<string>(x);
   }
}

Any help much appreciated.
Thanks in advance!

--
Daniel
A: Because it messes up the order in which people normally read text.
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