使用Boost Spirit X3解析变体图

时间:2018-12-28 04:20:28

标签: c++ boost c++14 boost-spirit boost-spirit-x3

我正在尝试(但失败)使用Boost Spirit X3通过以下代码来解析map<int, variant<string, float>>

#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/home/x3.hpp>
#include <iostream>
#include <map>
#include <variant>
#include <string>

using namespace std;

namespace x3 = boost::spirit::x3;

int main() {
    auto variantRule = x3::rule<class VariantClass, x3::variant<std::string, float>>() = (*x3::alnum | x3::float_);

    auto pairRule = x3::rule<class PairClass, pair<int, x3::variant<std::string, float>>>() = x3::int_ >> ":" >> variantRule;

    auto mapRule = x3::rule<class MapClass, map<int, x3::variant<std::string, float>>>() = pairRule >>  * ( "," >> pairRule );

    string input = "1 : 1.0, 2 : hello, 3 : world";

    map<int, x3::variant<std::string, float>> variantMap;

    auto success = x3::phrase_parse(input.begin(), input.end(), mapRule, x3::space, variantMap);

    return 0;
}

由于某种原因,我无法解析pair<int, variant<string, float>>的地图。但是,我能够解析变体的向量,只有当我尝试解析变体的映射时,我的代码才会失败。值得一提的是,我还完成了X3教程。任何帮助将不胜感激。

编辑1

考虑到@liliscent的回答以及其他一些更改,我终于能够使它工作,这里是正确的代码:

#include <boost/spirit/home/x3/support/ast/variant.hpp>
#include <boost/fusion/adapted/std_pair.hpp>
#include <boost/spirit/home/x3.hpp>
#include <iostream>
#include <map>
#include <variant>
#include <string>

using namespace std;

namespace x3 = boost::spirit::x3;

int main() {
    auto stringRule = x3::rule<class StringClass, string>() = x3::lexeme[x3::alpha >> *x3::alnum];

    auto variantRule = x3::rule<class VariantClass, x3::variant<std::string, float>>() = (stringRule | x3::float_);

    auto pairRule = x3::rule<class PairClass, pair<int, x3::variant<std::string, float>>>() = x3::int_ >> ':' >> variantRule;

    auto mapRule = x3::rule<class MapClass, map<int, x3::variant<std::string, float>>>() = pairRule % ",";

    string input = "1 : 1.0, 2 : hello, 3 : world";

    map<int, x3::variant<std::string, float>> variantMap;

    auto bg = input.begin(), ed = input.end();

    auto success = x3::phrase_parse(bg, ed, mapRule, x3::space, variantMap) && bg == ed;

    if (!success) cout<<"Parsing not succesfull";

    return 0;
}

1 个答案:

答案 0 :(得分:3)

如果您想让spirit识别std::pairstd::map,则需要包括std::pair的融合适配器:

#include <boost/fusion/adapted/std_pair.hpp>

这应该可以解决您的compilation problem。但是您的代码中还有其他问题,该规则(*x3::alnum | x3::float_);不能满足您的要求,因为左侧部分可以直接匹配为空。您需要重新考虑如何定义此标识符。

此外,写pairRule % ","比写pairRule >> * ( "," >> pairRule );更好。

您应该将输入作为左值迭代器开始传递,因为这样它将在解析期间进行高级处理,以便您可以检查解析器是否提前终止。