add <cstring> and <cwchar> compatible constexpr functions

sprout/cstring/strncpy.hpp

@@ -0,0 +1,49 @@
+/*=============================================================================
+  Copyright (c) 2011-2014 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  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 SPROUT_CSTRING_STRNCPY_HPP
+#define SPROUT_CSTRING_STRNCPY_HPP
+
+#include <iterator>
+#include <sprout/config.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename OutputCStrIterator, typename CStrIterator>
+		inline SPROUT_CXX14_CONSTEXPR OutputCStrIterator
+		strncpy(OutputCStrIterator s1, CStrIterator s2, std::size_t n) {
+			typedef typename std::iterator_traits<OutputCStrIterator>::value_type value_type;
+			OutputCStrIterator result = s1;
+			while (n) {
+				--n;
+				if (!(*s1++ = *s2++)) {
+					break;
+				}
+			}
+			while (n) {
+				--n;
+				*s1++ = value_type();
+			}
+			return result;
+		}
+	}	// namespace detail
+
+	// 7.21.2.4 The strncpy function
+	//
+	inline SPROUT_CXX14_CONSTEXPR char*
+	strncpy(char* s1, char const* s2, std::size_t n) {
+		return sprout::detail::strncpy(s1, s2, n);
+	}
+
+	template<typename Elem>
+	inline SPROUT_CXX14_CONSTEXPR Elem*
+	strncpy(Elem* s1, Elem const* s2, std::size_t n) {
+		return sprout::detail::strncpy(s1, s2, n);
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_CSTRING_STRNCPY_HPP