// In header: <boost/log/sinks/basic_sink_frontend.hpp>

struct formatting_context {
  // member classes/structs/unions
  class cleanup_guard {
  public:
    // construct/copy/destruct
    explicit cleanup_guard(formatting_context &) noexcept;
    cleanup_guard(cleanup_guard const &) = delete;
    cleanup_guard & operator=(cleanup_guard const &) = delete;
    ~cleanup_guard();
  };
  // construct/copy/destruct
  formatting_context();
  formatting_context(unsigned int, std::locale const &, 
                     formatter_type const &);
  // public data members
  const unsigned int m_Version;  // Object version. 
  string_type m_FormattedRecord;  // Formatted log record storage. 
  stream_type m_FormattingStream;  // Formatting stream. 
  formatter_type m_Formatter;  // Formatter functor. 
};