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1 | // Copyright 2013 Antony Polukhin |
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 | #include <cassert> | |
16 | ||
17 | struct to_long_double_functor: boost::static_visitor<long double> { | |
18 | template <class T> | |
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); | |
23 | } | |
24 | }; | |
25 | ||
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); | |
30 | } | |
31 | ||
32 | int main() { | |
33 | boost::variant<char, int, std::string> v1('0'), v2("10.0001"), v3(1); | |
34 | ||
35 | long double sum = to_long_double(v1) + to_long_double(v2) + to_long_double(v3); | |
36 | assert(sum > 11 && sum < 11.1); | |
37 | } | |
38 | ||
39 | //] [/lexical_cast_variant_to_long_double] |