使用 boost Spirit 解析为 STL 向量

Question

我正在学习 Boost Spirit 2，我不明白为什么我不能将两个整数的序列解析为 int 的 STL 向量。从 >> 运算符的文档中（here) I know the attribute of the grammar int_ >> int_ should be vector<int>. And from the attribute notation documentation 我知道 "The notation of vector<A> stands for any STL container holding elements of type A".

然而，当我尝试向 int_ >> int_ 添加一个将 std::vector 作为其属性的操作时，编译失败。

在其他错误消息中，它表示：/usr/include/boost/bind/mem_fn_template.hpp:163:7: note: no known conversion for argument 2 from ‘boost::fusion::vector<int, int>’ to ‘const std::vector<int>&’

我知道 this question ("Getting boost::spirit::qi to use stl containers")，但那里的解决方案 - 包括 std_tuple.hpp - 没有改变任何东西。

这是为什么？

#include <iostream>
#include <string>
#include <vector>

#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/bind.hpp>

namespace client
{
    namespace qi = boost::spirit::qi;
    namespace ascii = boost::spirit::ascii;

    class ParserActions
    {
    public:
        void printivec (std::vector<int> const& ivec)
        {
            std::cout << "We see " << ivec.size() << " integers" << std::endl;
        }
    };

    template <typename Iterator>
    bool parse_ivec(Iterator first, Iterator last)
    {
        using ascii::space;

        ParserActions actionContainer;

        auto two_ints = (qi::int_ >> qi::int_);

        bool r = qi::parse(
            first,                          /*< start iterator >*/
            last,                           /*< end iterator >*/
            two_ints[boost::bind(&ParserActions::printivec,&actionContainer,_1)]
            );

        return first == last && r;
    }
}

int main()
{
    std::string str = "12 13";

    if (client::parse_ivec(str.begin(),str.end()))
        std::cout << "Parsing succeeded\n";
    else
        std::cout << "Parsing failed!\n";

    return 0;
}

Answer 1

int_ >> int_ 合成一个 int 元组，int.¹

如果你想强制合成一个容器，让它repeat(2) [ int_ ]表达出来。

Sidenote: As you'll see below, there's room for attribute compatibility even if the bound attribute is a cotainer, so you don't need to.

Sidenote: auto with parser expressions is asking undefined behaviour: Assigning parsers to auto variables

Sidenote: your input uses space delimiter, but the parser doesn't. That will never work.

您的代码示例似乎与目标关系不大，所以这是我的小示例：

1。 vector<int>:

Live On Coliru

#include <boost/spirit/include/qi.hpp>
using Vec = std::vector<int>;
namespace qi = boost::spirit::qi;

template <typename It> Vec parse_ivec(It first, It last) {
    Vec v;
    if (qi::phrase_parse(first, last,  qi::int_ >> qi::int_ >> qi::eoi, qi::space, v))
        return v;
    throw std::runtime_error("Parse failed");
}

Vec parse_ivec(std::string const& r) { return parse_ivec(begin(r), end(r)); }

int main() {
    for (int i : parse_ivec("12 13")) {
        std::cout << i << "\n";
    }
}

版画

12
13

2。改编结构

或者，如果你想要一个结构，而不是 std::vector<>:

Live On Coliru

#include <boost/fusion/adapted/struct.hpp>
struct Vec { int a, b; };
BOOST_FUSION_ADAPT_STRUCT(Vec, a, b)

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

template <typename It> Vec parse_ivec(It first, It last) {
    Vec v;
    if (qi::phrase_parse(first, last,  qi::int_ >> qi::int_ >> qi::eoi, qi::space, v))
        return v;
    throw std::runtime_error("Parse failed");
}

Vec parse_ivec(std::string const& r) { return parse_ivec(begin(r), end(r)); }

int main() {
    Vec vec = parse_ivec("12 13");
    std::cout << vec.a << " " << vec.b << "\n";
}

版画

12 13

3。 std::tuple<int, int>:

Live On Coliru

#include <boost/fusion/adapted/std_tuple.hpp>
using Vec = std::tuple<int, int>;

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

template <typename It> Vec parse_ivec(It first, It last) {
    Vec v;
    if (qi::phrase_parse(first, last,  qi::int_ >> qi::int_ >> qi::eoi, qi::space, v))
        return v;
    throw std::runtime_error("Parse failed");
}

Vec parse_ivec(std::string const& r) { return parse_ivec(begin(r), end(r)); }

int main() {
    Vec vec = parse_ivec("12 13");
    std::cout << std::get<0>(vec) << " " << std::get<1>(vec) << "\n";
}

版画

12 13

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¹ 从技术上讲，Fusion 序列可以与许多类型（如 std::pair）或您自己的类型相兼容。