optional/doc/23_ref_optional_io.qbk

[/
    Boost.Optional

    Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
    Copyright (c) 2015 Andrzej Krzemienski

    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)
]

[section:io_header Header <boost/optional/optional_io.hpp>]

[section:io_synop Synopsis]
```
#include <istream>
#include <ostream>
#include <boost/optional/optional.hpp>

namespace boost {

template <class CharType, class CharTrait, class T>
  std::basic_ostream<CharType, CharTrait>&
  operator<<(std::basic_ostream<CharType, CharTrait>& out, optional<T> const& v); ``[link reference_operator_ostream __GO_TO__]``

  template <class CharType, class CharTrait>
  std::basic_ostream<CharType, CharTrait>&
  operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t const&); ``[link reference_operator_ostream_none __GO_TO__]``

template<class CharType, class CharTrait, class T>
  std::basic_istream<CharType, CharTrait>&
  operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v); ``[link reference_operator_istream __GO_TO__]``

} // namespace boost
```

[endsect]

[section:io_semantics Detailed semantics]


[#reference_operator_ostream]

```
template <class CharType, class CharTrait, class T>
std::basic_ostream<CharType, CharTrait>&
operator<<(std::basic_ostream<CharType, CharTrait>& out, optional<T> const& v);
```

* [*Effect:] Outputs an implementation-defined string. The output contains the information about whether the optional object contains a value or not. If `v` contains a value, the output contains result of calling `out << *v`.
* [*Returns:] `out`.

__SPACE__
[#reference_operator_ostream_none]

```
template <class CharType, class CharTrait, class T>
std::basic_ostream<CharType, CharTrait>&
operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t);
```

* [*Effect:] Outputs an implementation-defined string.
* [*Returns:] `out`.

__SPACE__
[#reference_operator_istream]

```
template <class CharType, class CharTrait, class T>
std::basic_ostream<CharType, CharTrait>&
operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v);
```

* [*Requires:] `T` is __STD_DEFAULT_CONSTRUCTIBLE__ and __MOVE_CONSTRUCTIBLE__.
* [*Effect:] Reads the value of optional object from `in`. If the string representation indicates that the optional object should contain a value, `v` contains a value and its contained value is obtained as if by default-constructing an object `o` of type `T` and then calling `in >> o`; otherwise `v` does not contain a value, and the previously contained value (if any) has been destroyed.
* [*Returns:] `out`.

[endsect]
[endsect]