math/tools/convert_from_string.hpp

0001 //  Copyright John Maddock 2016.
0002 //  Copyright Matt Borland 2023.
0003 //  Use, modification and distribution are subject to the
0004 //  Boost Software License, Version 1.0. (See accompanying file
0005 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006
0007 #ifndef BOOST_MATH_TOOLS_CONVERT_FROM_STRING_INCLUDED
0008 #define BOOST_MATH_TOOLS_CONVERT_FROM_STRING_INCLUDED
0009
0010 #ifdef _MSC_VER
0011 #pragma once
0012 #endif
0013
0014 #include <boost/math/tools/config.hpp>
0015 #include <type_traits>
0016 #ifndef BOOST_MATH_STANDALONE
0017
0018 #if defined(_MSC_VER) || defined(__GNUC__)
0019 # pragma push_macro( "I" )
0020 # undef I
0021 #endif
0022
0023 #include <boost/lexical_cast.hpp>
0024
0025 #if defined(_MSC_VER) || defined(__GNUC__)
0026 # pragma pop_macro( "I" )
0027 #endif
0028
0029 #endif
0030
0031 namespace boost{ namespace math{ namespace tools{
0032
0033    template <class T>
0034    struct convert_from_string_result
0035    {
0036       typedef typename std::conditional<std::is_constructible<T, const char*>::value, const char*, T>::type type;
0037    };
0038
0039    template <class Real>
0040    Real convert_from_string(const char* p, const std::false_type&)
0041    {
0042       #ifdef BOOST_MATH_NO_LEXICAL_CAST
0043
0044       // This function should not compile, we don't have the necessary functionality to support it:
0045       static_assert(sizeof(Real) == 0, "boost.lexical_cast is not supported in standalone mode.");
0046       (void)p; // Suppresses -Wunused-parameter
0047       return Real(0);
0048
0049       #elif defined(BOOST_MATH_USE_CHARCONV_FOR_CONVERSION)
0050
0051       if constexpr (std::is_arithmetic_v<Real>)
0052       {
0053          Real v {};
0054          std::from_chars(p, p + std::strlen(p), v);
0055
0056          return v;
0057       }
0058       else
0059       {
0060          return boost::lexical_cast<Real>(p);
0061       }
0062
0063       #else
0064
0065       return boost::lexical_cast<Real>(p);
0066
0067       #endif
0068    }
0069    template <class Real>
0070    constexpr const char* convert_from_string(const char* p, const std::true_type&) noexcept
0071    {
0072       return p;
0073    }
0074    template <class Real>
0075    constexpr typename convert_from_string_result<Real>::type convert_from_string(const char* p) noexcept((std::is_constructible<Real, const char*>::value))
0076    {
0077       return convert_from_string<Real>(p, std::is_constructible<Real, const char*>());
0078    }
0079
0080 } // namespace tools
0081 } // namespace math
0082 } // namespace boost
0083
0084 #endif // BOOST_MATH_TOOLS_CONVERT_FROM_STRING_INCLUDED
0085