output-stream-wrapper.h

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2010 University of Washington
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifndef OUTPUT_STREAM_WRAPPER_H
#define OUTPUT_STREAM_WRAPPER_H

#include <fstream>
#include "ns3/object.h"
#include "ns3/ptr.h"
#include "ns3/simple-ref-count.h"

namespace ns3 {

/*
 * @brief A class encapsulating an STL output stream.
 *
 * This class wraps a pointer to a C++ std::ostream and provides 
 * reference counting of the object.  This class is recommended for users 
 * who want to pass output streams in the ns-3 APIs, such as in callbacks
 * or tracing.
 *
 * This class is motivated by the fact that in C++, copy and assignment of 
 * iostreams is forbidden by std::basic_ios<>, because it is not possible 
 * to predict the semantics of the stream desired by a user.
 *
 * When writing traced information to a file, the tempting ns-3 idiom is to 
 * create a bound callback with an ofstream as the bound object.  Unfortunately,
 * this implies a copy construction in order to get the ofstream object into the
 * callback.  This operation, as mentioned above, is forbidden by the STL.
 * Using this class in ns-3 APIs is generally preferable to passing global 
 * pointers to ostream objects, or passing a pointer to a stack allocated 
 * ostream (which creates object lifetime issues). 
 *
 * One could imagine having this object inherit from stream to get the various
 * overloaded operator<< defined, but we're going to be using a
 * Ptr<OutputStreamWrapper> when passing this object around.  In this case, the 
 * Ptr<> wouldn't understand the operators and we would have to dereference it
 * to access the underlying object methods.  Since we would have to dereference
 * the Ptr<>, we don't bother and just expect the user to Get a saved pointer
 * to an ostream and dereference it him or herself.  As in:
 *
 * \verbatim
 *   void 
 *   TraceSink (Ptr<OutputStreamWrapper> streamWrapper, Ptr<const Packet> packet)
 *   {
 *     std::ostream *stream = streamWrapper->GetStream ();
 *     *stream << "got packet" << std::endl;
 *   }
 * \endverbatim
 *
 *
 * This class uses a basic ns-3 reference counting base class but is not 
 * an ns3::Object with attributes, TypeId, or aggregation.
 */
class OutputStreamWrapper : public SimpleRefCount<OutputStreamWrapper>
{
public:
  OutputStreamWrapper (std::string filename, std::ios::openmode filemode);
  OutputStreamWrapper (std::ostream* os);
  ~OutputStreamWrapper ();

  std::ostream *GetStream (void);

private:
  std::ostream *m_ostream;
  bool m_destroyable;
};

} // namespace ns3

#endif /* OUTPUT_STREAM_WRAPPER_H */