1 // Copyright 2013 Antony Polukhin
3 // Distributed under the Boost Software License, Version 1.0.
4 // (See the accompanying file LICENSE_1_0.txt
5 // or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
8 //[lexical_cast_variant_to_long_double
10 In this example we'll make a `to_long_double` method that converts value of the Boost.Variant to `long double`.
13 #include <boost/lexical_cast.hpp>
14 #include <boost/variant.hpp>
17 struct to_long_double_functor: boost::static_visitor<long double> {
19 long double operator()(const T& v) const {
20 // Lexical cast has many optimizations including optimizations for situations that usually
21 // occur in generic programming, like std::string to std::string or arithmetic type to arithmetic type conversion.
22 return boost::lexical_cast<long double>(v);
26 // Throws `boost::bad_lexical_cast` if value of the variant is not convertible to `long double`
27 template <class Variant>
28 long double to_long_double(const Variant& v) {
29 return boost::apply_visitor(to_long_double_functor(), v);
33 boost::variant<char, int, std::string> v1('0'), v2("10.0001"), v3(1);
35 long double sum = to_long_double(v1) + to_long_double(v2) + to_long_double(v3);
36 assert(sum > 11 && sum < 11.1);
39 //] [/lexical_cast_variant_to_long_double]