| 1 | // Copyright Antony Polukhin, 2013-2024. |
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| 2 | |
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| 3 | // Distributed under the Boost Software License, Version 1.0. |
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| 4 | // (See the accompanying file LICENSE_1_0.txt |
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| 5 | // or a copy at <http://www.boost.org/LICENSE_1_0.txt>.) |
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| 6 | |
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| 7 | |
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| 8 | //[lexical_cast_variant_to_long_double |
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| 9 | /*` |
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| 10 | In this example we'll make a `to_long_double` method that converts value of the Boost.Variant to `long double`. |
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| 11 | */ |
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| 12 | |
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| 13 | #include <boost/lexical_cast.hpp> |
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| 14 | #include <boost/variant.hpp> |
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| 15 | |
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| 16 | struct to_long_double_functor: boost::static_visitor<long double> { |
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| 17 | template <class T> |
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| 18 | long double operator()(const T& v) const { |
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| 19 | // Lexical cast has many optimizations including optimizations for situations that usually |
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| 20 | // occur in generic programming, like std::string to std::string or arithmetic type to arithmetic type conversion. |
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| 21 | return boost::lexical_cast<long double>(v); |
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| 22 | } |
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| 23 | }; |
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| 24 | |
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| 25 | // Throws `boost::bad_lexical_cast` if value of the variant is not convertible to `long double` |
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| 26 | template <class Variant> |
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| 27 | long double to_long_double(const Variant& v) { |
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| 28 | return boost::apply_visitor(to_long_double_functor(), v); |
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| 29 | } |
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| 30 | |
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| 31 | int main() { |
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| 32 | boost::variant<char, int, std::string> v1('0'), v2("10.0001" ), v3(1); |
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| 33 | |
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| 34 | const long double sum = to_long_double(v: v1) + to_long_double(v: v2) + to_long_double(v: v3); |
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| 35 | if (11 < sum && sum < 11.1) { |
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| 36 | return 0; // OK, as expected |
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| 37 | }; |
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| 38 | |
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| 39 | return 1; // FAIL |
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| 40 | } |
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| 41 | |
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| 42 | //] [/lexical_cast_variant_to_long_double] |
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| 43 | |
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