All classes in the \cgal\ kernel provide input and output operators for
IO streams.  Classes external to \cgal\ are also supported, by means of \ccc{oformat} (Section \ref{sec:iofornoncgaltypes}).
The basic task of such an operator is to produce a
representation of an object that can be written as a sequence of
characters on devices as a console, a file, or a pipe. In \cgal\
we distinguish between  a raw ascii, a raw binary and a
pretty printing format.

\ccEnum{enum Mode {ASCII = 0, BINARY, PRETTY};}{}


In \ccc{ASCII} mode, objects are written as
a set of  numbers, e.g.\ the coordinates of a point or
the coefficients of a line, in a machine independent format.
In \ccc{BINARY} mode,
data are written in a binary format, e.g.\ a double is represented
as a sequence of four byte. The format depends on the machine.
The mode  \ccc{PRETTY}
serves mainly for debugging as the type of the geometric
object is written, as well as the data defining the object. For example
for a point at the origin with Cartesian double coordinates, the output
would be \ccc{PointC2(0.0, 0.0)}.  At the moment \cgal\ does not
provide input operations for pretty printed data. By default a stream
is in {\sc ascii} mode.

\ccThree{IO::Mode}{set_mode(std::ios& s, IO::Mode m);}{}

\cgal\ provides the following functions to modify the mode of an IO stream.

\ccFunction{IO::Mode  set_mode(std::ios& s, IO::Mode m);}{}

\ccFunction{IO::Mode  set_ascii_mode(std::ios& s);}{}
\ccGlue
\ccFunction{IO::Mode  set_binary_mode(std::ios& s);}{}
\ccGlue
\ccFunction{IO::Mode  set_pretty_mode(std::ios& s);}{}

The following functions allow to test whether a stream is in a certain mode.

\ccFunction{IO::Mode  get_mode(std::ios& s);}{}

\ccFunction{bool is_ascii(std::ios& s);}{}
\ccGlue
\ccFunction{bool is_binary(std::ios& s);}{}
\ccGlue
\ccFunction{bool is_pretty(std::ios& s);}{}


%\newpage

\ccThree{ostream&}{operator<<( const Class &c);}{}

%\begin{ccClass} {ostream}
\section{Output Operator}
%\ccCreationVariable{os}

%\ccDefinition
\cgal\  defines output operators for classes that are derived
from the class \ccStyle{ostream}. This allows to write to ostreams
as \ccStyle{cout} or \ccStyle{cerr}, as well as to strstreams
and fstreams.
The output operator is defined for all classes in the \cgal\ kernel and for the class \ccc{Color} as well.
Let \ccc{os}  be an output stream.

\ccFunction{ostream& operator<<(ostream& os, Class c);}
{Inserts object \ccStyle{c} in the stream \ccc{os}. Returns \ccc{os}.}


\ccExample

\begin{ccExampleCode}

#include <CGAL/basic.h>
#include <iostream>
#include <fstream>

#include <CGAL/Cartesian.h>
#include <CGAL/Segment_2.h>

typedef CGAL::Point_2< CGAL::Cartesian<double> >     Point;
typedef CGAL::Segment_2< CGAL::Cartesian<double> >   Segment;

int main()
{
    Point p(0,1), q(2,2);
    Segment s(p,q);

    CGAL::set_pretty_mode(std::cout);
    std::cout << p << std::endl << q  << std::endl;

    std::ofstream f("data.txt");
    CGAL::set_binary_mode(f);
    f << s << p ;

    return 1;
}
\end{ccExampleCode}
%\end{ccClass}


%\newpage
%\begin{ccClass} {istream}
\section{Input Operator}


%\ccDefinition
\cgal\  defines input operators for classes that are derived
from the class \ccStyle{istream}. This allows to read from istreams
as \ccStyle{cin}, as well as from strstreams and fstreams.
The input operator is defined for all classes in the \cgal\ kernel.
Let \ccc{is} be an input stream.

\ccFunction{istream& operator>>(istream& is, Class c);}
   {Extracts object \ccStyle{c} from the stream \ccc{is}. Returns \ccc{is}.}


\ccExample

\begin{ccExampleCode}

#include <CGAL/basic.h>
#include <iostream>
#include <fstream>

#include <CGAL/Cartesian.h>
#include <CGAL/Segment_2.h>

typedef CGAL::Point_2< CGAL::Cartesian<double> >     Point;
typedef CGAL::Segment_2< CGAL::Cartesian<double> >   Segment;

int
main()
{
    Point p, q;
    Segment s;

    CGAL::set_ascii_mode(std::cin);
    std::cin >> p >> q;

    std::ifstream f("data.txt");
    CGAL::set_binary_mode(f);
    f >> s >> p;

    return 1;
}
\end{ccExampleCode}
%\end{ccClass}

\section{IO for non-\cgal\ types\label{sec:iofornoncgaltypes}}


\subsection{Using Output Formatting}
To ensure that non-\cgal\ types are formatted correctly (i.e., respecting \ccc{IO::Mode}), \ccc{oformat} can be used. For types with a \ccc{Output_rep} specialization, the respective output routine of \ccc{Output_rep} will be called by \ccc{oformat}. Otherwise, the stream output operator will be called.

\ccExample
\begin{ccExampleCode}
std::cout << CGAL::oformat( myobject );
\end{ccExampleCode}

Optional, you can provide a second template parameter \texttt{F} as a formatting tag:

\ccExample
\begin{ccExampleCode}
std::cout << CGAL::oformat( myobject, My_formatting_tag() );
\end{ccExampleCode}

For a list of formatting tags supported by the type \texttt{T}, please refer to the documentation of the respective type.

\subsection{Customizing Output Formatting}
In some situations, you want to control the output formatting for a type \texttt{T}. For external types (third party libraries etc.), there might be problems if their stream output operator does not respect \ccc{IO::Mode}. The purpose of \ccc{Output_rep} is to provide a way to control output formatting that works independently of the object's stream output operator.

Instead of putting \texttt{T} directly into an output stream, \texttt{T} is wrapped into an output representation \ccc{Output_rep}. For convenience, a function \ccc{oformat} exists which constructs an instance of \ccc{Output_rep}.

If you do not specialize \ccc{Output_rep} for \texttt{T}, \texttt{T}'s stream output operator is called from within \ccc{Output_rep}, by default. If you want another behaviour for your type \texttt{T}, you have to provide a specialization for that type. Furthermore, you can provide specializations with a second template parameter (a formatting tag). The second template parameter defaults to \ccc{Null_tag} and means \textit{default behaviour}.

For example, specializing \ccc{Output_rep} for \ccc{CORE::BigRat} (without a formatting tag parameter) could look like this:

\ccExample
\begin{ccExampleCode}
template <class F>
class Output_rep< ::CORE::BigRat, F> {
    const ::CORE::BigRat& t;
public:
    Output_rep( const ::CORE::BigRat& tt) : t(tt) {}

    std::ostream& operator()( std::ostream& out) const {
        switch (get_mode(out)) {
        case IO::PRETTY:{
            if(CGAL_CORE_DENOMINATOR(t) == ::CORE::BigRat(1))
                return out <<CGAL_CORE_NUMERATOR(t);
            else
                return out << CGAL_CORE_NUMERATOR(t)
                           << "/"
                           << CGAL_CORE_DENOMINATOR(t);
            break;
        }

        default:
            return out << CGAL_CORE_NUMERATOR(t)
                       << "/"
                       << CGAL_CORE_DENOMINATOR(t);
        }
    }
};
\end{ccExampleCode}