1 | // Copyright Antony Polukhin, 2013-2024. |
2 | |
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>.) |
6 | |
7 | |
8 | //[lexical_cast_variant_to_long_double |
9 | /*` |
10 | In this example we'll make a `to_long_double` method that converts value of the Boost.Variant to `long double`. |
11 | */ |
12 | |
13 | #include <boost/lexical_cast.hpp> |
14 | #include <boost/variant.hpp> |
15 | |
16 | struct to_long_double_functor: boost::static_visitor<long double> { |
17 | template <class T> |
18 | long double operator()(const T& v) const { |
19 | // Lexical cast has many optimizations including optimizations for situations that usually |
20 | // occur in generic programming, like std::string to std::string or arithmetic type to arithmetic type conversion. |
21 | return boost::lexical_cast<long double>(v); |
22 | } |
23 | }; |
24 | |
25 | // Throws `boost::bad_lexical_cast` if value of the variant is not convertible to `long double` |
26 | template <class Variant> |
27 | long double to_long_double(const Variant& v) { |
28 | return boost::apply_visitor(to_long_double_functor(), v); |
29 | } |
30 | |
31 | int main() { |
32 | boost::variant<char, int, std::string> v1('0'), v2("10.0001" ), v3(1); |
33 | |
34 | const long double sum = to_long_double(v: v1) + to_long_double(v: v2) + to_long_double(v: v3); |
35 | if (11 < sum && sum < 11.1) { |
36 | return 0; // OK, as expected |
37 | }; |
38 | |
39 | return 1; // FAIL |
40 | } |
41 | |
42 | //] [/lexical_cast_variant_to_long_double] |
43 | |