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UnbufferedStreamBuf.h
//
// UnufferedStreamBuf.h
//
// $Id: //poco/1.3/Foundation/include/Poco/UnbufferedStreamBuf.h#3 $
//
// Library: Foundation
// Package: Streams
// Module:  StreamBuf
//
// Definition of template BasicUnbufferedStreamBuf and class UnbufferedStreamBuf.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_UnbufferedStreamBuf_INCLUDED
#define Foundation_UnbufferedStreamBuf_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/StreamUtil.h"
#include <streambuf>
#include <iosfwd>
#include <ios>


namespace Poco {


template <typename ch, typename tr> 
00054 class BasicUnbufferedStreamBuf: public std::basic_streambuf<ch, tr>
      /// This is an implementation of an unbuffered streambuf
      /// that greatly simplifies the implementation of
      /// custom streambufs of various kinds.
      /// Derived classes only have to override the methods
      /// readFromDevice() or writeToDevice().
{
protected:
      typedef std::basic_streambuf<ch, tr> Base;
      typedef std::basic_ios<ch, tr> IOS;
      typedef ch char_type;
      typedef tr char_traits;
      typedef typename Base::int_type int_type;
      typedef typename Base::pos_type pos_type;
      typedef typename Base::off_type off_type;
      typedef typename IOS::openmode openmode;

public:
      BasicUnbufferedStreamBuf():
            _pb(char_traits::eof()),
            _ispb(false)
      {
            this->setg(0, 0, 0);
            this->setp(0, 0);
      }

      ~BasicUnbufferedStreamBuf()
      {
      }

      virtual int_type overflow(int_type c)
      {
            if (c != char_traits::eof()) 
                  return writeToDevice(char_traits::to_char_type(c));
            else
                  return c;
      }

      virtual int_type underflow()
      {
            if (_ispb)
            {
            return _pb;
            }
            else
            {
            int_type c = readFromDevice();
            if (c != char_traits::eof())
            {
                  _ispb = true;
                  _pb   = c;
            }
            return c;
            }
      }

      virtual int_type uflow()
      {
            if (_ispb)
            {
                  _ispb = false;
                  return _pb;
            }
            else
            {
            int_type c = readFromDevice();
            if (c != char_traits::eof())
            {
                  _pb = c;
            }
            return c;
            }
      }

      virtual int_type pbackfail(int_type c)
      {
            if (_ispb)
            {
            return char_traits::eof();
            }
            else
            {
            _ispb = true;
            _pb   = c;
            return c;
            }
      }
      
00142       virtual std::streamsize xsgetn(char_type* p, std::streamsize count)
            /// Some platforms (for example, Compaq C++) have buggy implementations of 
            /// xsgetn that handle null buffers incorrectly.
            /// Anyway, it does not hurt to provide an optimized implementation
            /// of xsgetn for this streambuf implementation.
      {
            std::streamsize copied = 0;
            while (count > 0)
            {
                  int_type c = uflow();
                  if (c == char_traits::eof()) break;
                  *p++ = char_traits::to_char_type(c);
                  ++copied;
                  --count;
            }
            return copied;
      }

protected:
      static int_type charToInt(char_type c)
      {
            return char_traits::to_int_type(c);
      }

private:
      virtual int_type readFromDevice()
      {
            return char_traits::eof();
      }
      
      virtual int_type writeToDevice(char_type)
      {
            return char_traits::eof();
      }

      int_type _pb;
      bool     _ispb;
      
      BasicUnbufferedStreamBuf(const BasicUnbufferedStreamBuf&);
      BasicUnbufferedStreamBuf& operator = (const BasicUnbufferedStreamBuf&);
};


//
// We provide an instantiation for char
//
typedef BasicUnbufferedStreamBuf<char, std::char_traits<char> > UnbufferedStreamBuf;


} // namespace Poco


#endif // Foundation_UnbufferedStreamBuf_INCLUDED

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