From 26f20bd8e5e8ca7b41f24ff87e4c8c6ce24d29b4 Mon Sep 17 00:00:00 2001
From: Nikita Kniazev <nok.raven@gmail.com>
Date: Tue, 3 Dec 2019 19:35:14 +0300
Subject: [PATCH] Use <version> to determine standard library

---
 .../boost/config/detail/select_stdlib_config.hpp  | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/boost/config/detail/select_stdlib_config.hpp b/include/boost/config/detail/select_stdlib_config.hpp
index 8db778c8..1a09dda1 100644
--- a/include/boost/config/detail/select_stdlib_config.hpp
+++ b/include/boost/config/detail/select_stdlib_config.hpp
@@ -11,10 +11,21 @@
 
 // locate which std lib we are using and define BOOST_STDLIB_CONFIG as needed:
 
-// First include <cstddef> to determine if some version of STLport is in use as the std lib
+// First, check if __has_include is available and <version> include can be located,
+// otherwise include <cstddef> to determine if some version of STLport is in use as the std lib
 // (do not rely on this header being included since users can short-circuit this header 
 //  if they know whose std lib they are using.)
-#ifdef __cplusplus
+#if defined(__cplusplus) && defined(__has_include)
+#  if __has_include(<version>)
+// It should be safe to include `<version>` when it is present without checking
+// the actual C++ language version as it consists solely of macro definitions.
+// [version.syn] p1: The header <version> supplies implementation-dependent
+// information about the C++ standard library (e.g., version number and release date).
+#    include <version>
+#  else
+#    include <cstddef>
+#  endif
+#elif defined(__cplusplus)
 #  include <cstddef>
 #else
 #  include <stddef.h>