// Logger.h - Абстракция
#include <string>

 // Опережающее объявление, позволяющее не включать файл LoggerImpl.h
class LoggerImpl;

class Logger
{
  public:
    Logger( LoggerImpl* p );
    virtual ~Logger( );
    virtual void log( string & str ) = 0;
  protected:
    LoggerImpl * pimpl;
};

class ConsoleLogger : public Logger
{
  public:
    ConsoleLogger();
    void log( string & str );
};

class FileLogger : public Logger
{
  public:
    FileLogger( string & file_name );
    void log( string & str );
  private:
    string file;
};

class SocketLogger : public Logger
{
  public:
    SocketLogger( string & remote_host, int remote_port );
    void log( string & str );
  private:
    string host;
    int    port;
};


// Logger.cpp - Абстракция
#include "Logger.h"
#include "LoggerImpl.h"

Logger::Logger( LoggerImpl* p ) : pimpl(p)
{ }

Logger::~Logger( )
{
    delete pimpl;
}

ConsoleLogger::ConsoleLogger() : Logger(
      #ifdef MT
        new MT_LoggerImpl()
      #else
        new ST_LoggerImpl()
      #endif
    )
{ }

void ConsoleLogger::log( string & str )
{
    pimpl->console_log( str);
}

FileLogger::FileLogger( string & file_name ) : Logger(
      #ifdef MT
        new MT_LoggerImpl()
      #else
        new ST_LoggerImpl()
      #endif
      ), file(file_name)
{ }

void FileLogger::log( string & str )
{
    pimpl->file_log( file, str);
}

SocketLogger::SocketLogger( string & remote_host, int remote_port ) : Logger(
      #ifdef MT
        new MT_LoggerImpl()
      #else
        new ST_LoggerImpl()
      #endif
       ), host(remote_host), port(remote_port)
{ }

void SocketLogger::log( string & str )
{
    pimpl->socket_log( host, port, str);
}


// LoggerImpl.h - Реализация
#include <string>

class LoggerImpl
{
  public:
    virtual ~LoggerImpl( ) {}
    virtual void console_log( string & str ) = 0;
    virtual void file_log( string & file, string & str ) = 0;
    virtual void socket_log( string & host, int port, string & str ) = 0;
};

class ST_LoggerImpl : public LoggerImpl
{
  public:
    void console_log( string & str );
    void file_log   ( string & file, string & str );
    void socket_log ( string & host, int port, string & str );
};

class MT_LoggerImpl : public LoggerImpl
{
  public:
    void console_log( string & str );
    void file_log   ( string & file, string & str );
    void socket_log ( string & host, int port, string & str );
};


// LoggerImpl.cpp - Реализация
#include <iostream>
#include "LoggerImpl.h"


void ST_LoggerImpl::console_log( string & str )
{
    cout << "Single-threaded console logger" << endl;
}

void ST_LoggerImpl::file_log( string & file, string & str )
{
    cout << "Single-threaded file logger" << endl;
}

void ST_LoggerImpl::socket_log( string & host, int port, string & str )
{
    cout << "Single-threaded socket logger" << endl;
};

void MT_LoggerImpl::console_log( string & str )
{
    cout << "Multithreaded console logger" << endl;
}

void MT_LoggerImpl::file_log( string & file, string & str )
{
    cout << "Multithreaded file logger" << endl;
}

void MT_LoggerImpl::socket_log( string & host, int port, string & str )
{
    cout << "Multithreaded socket logger" << endl;
}


// Main.cpp
#include <string>
#include "Logger.h"

int main()
{
    Logger * p = new FileLogger( string("log.txt"));
    p->log( string("message"));
    delete p;
    return 0;
}