cpp11/impl/string_at.hpp

0001 #ifndef BOOST_METAPARSE_V1_CPP11_IMPL_STRING_AT_HPP
0002 #define BOOST_METAPARSE_V1_CPP11_IMPL_STRING_AT_HPP
0003
0004 // Copyright Abel Sinkovics (abel@sinkovics.hu)  2016.
0005 // Distributed under the Boost Software License, Version 1.0.
0006 //    (See accompanying file LICENSE_1_0.txt or copy at
0007 //          http://www.boost.org/LICENSE_1_0.txt)
0008
0009 #include <boost/metaparse/limit_string_size.hpp>
0010
0011 namespace boost
0012 {
0013   namespace metaparse
0014   {
0015     namespace v1
0016     {
0017       namespace impl
0018       {
0019         template <int MaxLen, int Len, class T>
0020         constexpr T string_at(const T (&s)[Len], int n)
0021         {
0022           // "MaxLen + 1" adds the \0 character of the string literal to the
0023           // limit
0024           static_assert(Len <= MaxLen + 1, "String literal is too long.");
0025           return n >= Len - 1 ? T() : s[n];
0026         }
0027       }
0028     }
0029   }
0030 }
0031
0032 #ifdef BOOST_METAPARSE_V1_STRING_AT
0033 #  error BOOST_METAPARSE_V1_STRING_AT already defined
0034 #endif
0035 #define BOOST_METAPARSE_V1_STRING_AT \
0036   ::boost::metaparse::v1::impl::string_at<BOOST_METAPARSE_LIMIT_STRING_SIZE>
0037
0038 #endif
0039