Question

我的程序中有一个boost :: variant，它包含double，uint16_t，std::string等类型。我正在存储这些，我想使用{ {1}}生成/打印出来。我是boost::karma的新手，但我知道它适用于变体。我有什么选择呢？简单的语法/规则会产生什么样的？任何帮助都会很棒！

Answer 1

1。简洁规则

我能想到的绝对最简单的例子，展示业力甚至可以为您的特定变体动态合成auto_规则 ^[1]：

#include <boost/spirit/include/karma.hpp>    
namespace karma = boost::spirit::karma;

int main() {
    typedef boost::variant<double, unsigned int, std::string> V;

    for(auto v : { V{42u}, V{3.1416}, V{"Life Of Pi"} })
        std::cout << karma::format(karma::auto_, v) << "\n";
}

打印：

42
3.142
Life Of Pi

简单就是馅饼！

单独语法中的等效词： Live On Coliru

2。更复杂的样本

更复杂的语法（也是 Live On Coliru ），它向您展示了Spirit的属性兼容性如何规范DoTheRightThing™：

#include <boost/spirit/include/karma.hpp>

namespace karma = boost::spirit::karma;

typedef boost::variant<double, unsigned int, std::string> V;

struct gen : karma::grammar<boost::spirit::ostream_iterator, V()> {
    gen() : gen::base_type(start) 
    {
        using namespace karma;

        start = my_real | my_uint | my_text;

        my_uint = "The value is unsigned integral value (" << uint_ << ")";
        my_real = "The value is double precision floating point value (" << double_ << ")";
        my_text = "The value is an epos: '" << *quoted_char << "'";

        quoted_char = '\\' << char_("'") | graph | "\\x" << uint_generator<uint8_t, 16>();
    }
  private:
    karma::rule<boost::spirit::ostream_iterator, V()>           start;
    karma::rule<boost::spirit::ostream_iterator, double()>      my_real;
    karma::rule<boost::spirit::ostream_iterator, unsigned       int()>   my_uint;
    karma::rule<boost::spirit::ostream_iterator, std::string()> my_text;
    karma::rule<boost::spirit::ostream_iterator, uint8_t()>     quoted_char;
};

int main()
{
    for(auto v : { V{42u}, V{3.1416}, V{"It's a beautiful day!"} })
        std::cout << karma::format(gen(), v) << "\n";
}

打印：

The value is unsigned integral value (42)
The value is double precision floating point value (3.142)
The value is an epos: 'It\'s\x20a\x20beautiful\x20day!'

main也可以写成

int main() {
    std::cout << karma::format(gen() % "\n", std::vector<V>{42u,3.1416,"It's a beautiful day!"}) << "\n";
}

这应该可以让您了解Spirit Parser / Generator框架的多功能性。

^[1]只要存在自动解析器生成器特征; Spirit为各种类型提供了它们，包括uint，std::string，double和variant（还包括选项，矢量，地图，任何可以作为Fusion修改的内容）序列等等。）

c ++ boost :: spirit ::变种的karma规则

1 个答案:

1。简洁规则

2。更复杂的样本