[Boost-commit] svn:boost r4155

From: jefffaust_at_[hidden]
Date: 2007-05-21 08:08:00

Author: jefffaust
Date: 2007-05-21 08:07:59 EDT (Mon, 21 May 2007)
New Revision: 4155
URL: http://svn.boost.org/trac/boost/changeset/4155

Log:
initial checkin

Added:
   sandbox/explore/boost/explore/stream_state.hpp

Added: sandbox/explore/boost/explore/stream_state.hpp
==============================================================================
--- (empty file)
+++ sandbox/explore/boost/explore/stream_state.hpp	2007-05-21 08:07:59 EDT (Mon, 21 May 2007)
@@ -0,0 +1,74 @@
+//
+// stream_state.hpp - maintain user-defined state per stream.
+//
+// The single entry point, get_stream_state, wraps the arcane ios
+// interfaces xalloc, pword, and register_callback.
+//
+// Built, run, and tested on exactly one compiler (VC8).
+//
+// Copyright (c) 2007 Jeff Faust
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef stream_state_h_
+#define stream_state_h_
+
+#include <xiosbase> // TODO: is this a standard header?
+#include <memory>
+
+namespace explore
+{
+	// forward declaration for deletion callback
+	template<typename T>
+	T* get_stream_state(std::ios_base& stream, bool create);
+
+	namespace detail
+	{
+		// returns an index into the ios_base container of user-defined data.  This will
+		// create exactly one index per type T.
+		template<typename T>
+		int get_stream_state_index(std::ios_base& stream)
+		{
+			static int index = stream.xalloc();
+			return index;
+		}
+
+		// deletion callback for extra state
+		template<typename T>
+		void delete_extra_state(std::ios_base::event e, std::ios_base& stream, int arg)
+		{
+			if( std::ios_base::erase_event == e && arg == get_stream_state_index<T>(stream) )
+			{
+				delete get_stream_state<T>(stream);
+				stream.pword(arg) = 0;
+			}
+		}
+	}
+
+	// returns state information stored in the stream for the given type.  Will allocate
+	// state data if needed and create == true.  If create == false and the data does not
+	// already exist, it will return 0.
+	// T: the user-defined state class.  Must be default constructible.
+	template<typename T>
+	T* get_stream_state(std::ios_base& stream, bool create = true)
+	{
+		// grab reserved index
+		int index = detail::get_stream_state_index<T>(stream);
+
+		// grab state data at that index, casting from void*
+		T*& state = reinterpret_cast<T*&>(stream.pword(index));
+		if( !state && create )
+		{
+			// both creating a new T and registering the callback allocate memory.  Use
+			// auto_ptr to satisfy the strong exception guarantee.
+			std::auto_ptr<T> pt(new T);
+			stream.register_callback(detail::delete_extra_state<T>, index);
+			state = pt.release();
+		}
+		return state;
+	}
+}
+
+#endif