write.hpp

C++的一个好库。。。现在很流行

// (C) Copyright Jonathan Turkanis 2005.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)

// See http://www.boost.org/libs/iostreams for documentation.

namespace boost { namespace iostreams {

namespace detail {

template<typename T> 
struct write_device_impl;

template<typename T> 
struct write_filter_impl;

} // End namespace detail.

template<typename T>
bool put(T& t, typename char_type_of<T>::type c)
{
    typedef typename detail::unwrapped_type<T>::type unwrapped;
    return detail::write_device_impl<T>::inner<unwrapped>::put(detail::unwrap(t), c);
}

template<typename T>
inline std::streamsize write
    (T& t, const typename char_type_of<T>::type* s, std::streamsize n)
{
    typedef typename detail::unwrapped_type<T>::type unwrapped;
    return detail::write_device_impl<T>::inner<unwrapped>::write(detail::unwrap(t), s, n);
}

template<typename T, typename Sink>
inline std::streamsize
write( T& t, Sink& snk, const typename char_type_of<T>::type* s, 
       std::streamsize n )
{
    typedef typename detail::unwrapped_type<T>::type unwrapped;
    return detail::write_filter_impl<T>::inner<unwrapped>::write(detail::unwrap(t), snk, s, n);
}

namespace detail {

//------------------Definition of write_device_impl---------------------------//

template<typename T>
struct write_device_impl
    : mpl::if_<
          is_custom<T>,
          operations<T>,
          write_device_impl<
              BOOST_DEDUCED_TYPENAME
              dispatch<
                  T, ostream_tag, streambuf_tag, output
              >::type
          >
      >::type
    { };

template<>
struct write_device_impl<ostream_tag> {
    template<typename T>
    struct inner {
        static bool put(T& t, typename char_type_of<T>::type c)
        {
            typedef typename char_type_of<T>::type          char_type;
            typedef BOOST_IOSTREAMS_CHAR_TRAITS(char_type)  traits_type;
            return !traits_type::eq_int_type( t.rdbuf()->s.sputc(),
                                            traits_type::eof() );
        }

        static std::streamsize write
            (T& t, const typename char_type_of<T>::type* s, std::streamsize n)
        { return t.rdbuf()->sputn(s, n); }
    };
};

template<>
struct write_device_impl<streambuf_tag> {
    template<typename T>
    struct inner {
        static bool put(T& t, typename char_type_of<T>::type c)
        {
            typedef typename char_type_of<T>::type          char_type;
            typedef BOOST_IOSTREAMS_CHAR_TRAITS(char_type)  traits_type;
            return !traits_type::eq_int_type(t.sputc(c), traits_type::eof());
        }

        template<typename T>
        static std::streamsize write
            (T& t, const typename char_type_of<T>::type* s, std::streamsize n)
        { return t.sputn(s, n); }
    };
};

template<>
struct write_device_impl<output> {
    template<typename T>
    struct inner {
        static bool put(T& t, typename char_type_of<T>::type c)
        { return t.write(&c, 1) == 1; }

        template<typename T>
        static std::streamsize
        write(T& t, const typename char_type_of<T>::type* s, std::streamsize n)
        { return t.write(s, n); }
    };
};

//------------------Definition of write_filter_impl---------------------------//

template<typename T>
struct write_filter_impl
    : mpl::if_<
          is_custom<T>,
          operations<T>,
          write_filter_impl<
              BOOST_DEDUCED_TYPENAME
              dispatch<
                  T, multichar_tag, any_tag
              >::type
          >
      >::type
    { };

template<>
struct write_filter_impl<multichar_tag> {
    template<typename T>
    struct inner {
        template<typename Sink>
        static std::streamsize
        write( T& t, Sink& snk, const typename char_type_of<T>::type* s,
               std::streamsize n )
        { return t.write(snk, s, n); }
    };
};

template<>
struct write_filter_impl<any_tag> {
    template<typename T>
    struct inner {
        template<typename Sink>
        static std::streamsize
        write( T& t, Sink& snk, const typename char_type_of<T>::type* s,
               std::streamsize n )
        {
            for (std::streamsize off = 0; off < n; ++off)
                if (!t.put(snk, s[off]))
                    return off;
            return n;
        }
    };
};

} // End namespace detail.

} } // End namespaces iostreams, boost.