manip.cpp

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

template <typename Result>
class manip
{
public:
  typedef manip base_type;
  typedef std::ios_base::fmtflags flags_type;
  typedef Result result_type;

private:
  flags_type format_;
  flags_type mask_;
  result_type value_;

public:
  manip(flags_type format, flags_type mask)
    : format_(format)
    , mask_(mask)
  {}

  template <typename CharT>
  friend std::basic_istream<CharT>& operator>>(std::basic_istream<CharT>& is, manip<Result>& v)
  {
    is.setf(v.format_, v.mask_);
    is >> v.value_;
    return is;
  }
  operator result_type() const { return value_; }
};


template <typename Result>
class hex : public manip<Result>
{
public:
  hex()
    : hex::base_type(std::ios::hex, std::ios::basefield)
  {}
};


int main()
{
  int x = boost::lexical_cast<int>("123");
  std::cout << x << std::endl; // 123

  int y = boost::lexical_cast< hex<int> >("0xffff");
  std::cout << y << std::endl; // 65535
}