Add C++03 deprecation notice

include/boost/endian/arithmetic.hpp

@@ -27,6 +27,7 @@
 # pragma warning(disable:4365)  // conversion ... signed/unsigned mismatch
 #endif
 
+#include <boost/endian/detail/requires_cxx11.hpp>
 #include <boost/endian/buffers.hpp>
 #include <boost/core/scoped_enum.hpp>
 #include <boost/static_assert.hpp>

include/boost/endian/buffers.hpp

@@ -27,6 +27,7 @@
 # pragma warning(disable: 4127)  // conditional expression is constant
 #endif
 
+#include <boost/endian/detail/requires_cxx11.hpp>
 #include <boost/endian/detail/endian_store.hpp>
 #include <boost/endian/detail/endian_load.hpp>
 #include <boost/core/scoped_enum.hpp>

include/boost/endian/conversion.hpp

@@ -8,6 +8,7 @@
 #ifndef BOOST_ENDIAN_CONVERSION_HPP
 #define BOOST_ENDIAN_CONVERSION_HPP
 
+#include <boost/endian/detail/requires_cxx11.hpp>
 #include <boost/endian/detail/endian_reverse.hpp>
 #include <boost/endian/detail/endian_load.hpp>
 #include <boost/endian/detail/endian_store.hpp>

include/boost/endian/detail/requires_cxx11.hpp

@@ -0,0 +1,23 @@
+#ifndef BOOST_ENDIAN_DETAIL_REQUIRES_CXX11_HPP_INCLUDED
+#define BOOST_ENDIAN_DETAIL_REQUIRES_CXX11_HPP_INCLUDED
+
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || \
+    defined(BOOST_NO_CXX11_RVALUE_REFERENCES) || \
+    defined(BOOST_NO_CXX11_DECLTYPE) || \
+    defined(BOOST_NO_CXX11_CONSTEXPR) || \
+    defined(BOOST_NO_CXX11_NOEXCEPT) || \
+    defined(BOOST_NO_CXX11_SCOPED_ENUMS) || \
+    defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS)
+
+BOOST_PRAGMA_MESSAGE("C++03 support is deprecated in Boost.Endian 1.82 and will be removed in Boost.Endian 1.84.")
+
+#endif
+
+#endif // #ifndef BOOST_ENDIAN_DETAIL_REQUIRES_CXX11_HPP_INCLUDED