提升精神船长问题 [英] Boost spirit skipper issues

问题描述

我在使用提升精神船长时遇到了麻烦.

I have trouble with boost spirit skippers.

我需要解析这样的文件:

I need to parse a file like that :

ROW int
int [int, int]
int [int, int]
...

我能够毫无问题地解析它(感谢stackoverflow；)只有当我在第一个int之后添加一个'_'时.

I am able to parse it without problem (thanks to stackoverflow ;) only if I add an '_' after the first int.

事实上，我认为船长在第一个 int 之后吃掉了行尾，所以第一个和第二个(在第二行)看起来只有一个 int.我不明白如何保持 eol 但吃空间.我找到了使用自定义解析器的示例，例如 here 和这里.

In fact, I think the skipper eat the end of line after the first int, so the first and second (on second line) look as only one int. I don't understand how to keep eol but eat spaces. I've found examples to use a custom parser like here and here.

我尝试了 qi::blank，自定义解析器，带有一个单一规则 lit(' ')不管我用什么船长，space 和 eol 总是吃.

I tried qi::blank, custom parser with one single rule lit(' ') No matter what skipper I use, space and eol are always eat.

我的语法是:

一行:

struct rowType
{
    unsigned int number;
    std::list<unsigned int> list;
};

存储在结构中的完整问题:

the full problem stored in a structure :

struct problemType
{
    unsigned int ROW;
    std::vector<rowType> rows;
};

行解析器:

template<typename Iterator>
struct row_parser : qi::grammar<Iterator, rowType(), qi::space_type>
{
    row_parser() : row_parser::base_type(start)
    {

        list  = '[' >> -(qi::int_ % ',') >> ']';
        start = qi::int_ >> list;
    }

    qi::rule<Iterator, rowType(), qi::space_type> start;
    qi::rule<Iterator, std::list<unsigned int>(), qi::space_type> list;
};

和问题解析器:

template<typename Iterator>
struct problem_parser : qi::grammar<Iterator,problemType(),qi::space_type>
{

    problem_parser() : problem_parser::base_type(start)
    {
        using boost::phoenix::bind;
        using qi::lit;

        start = qi::int_ >> lit('_') >> +(row);

        //BOOST_SPIRIT_DEBUG_NODE(start);
    }

    qi::rule<Iterator, problemType(),qi::space_type> start;
    row_parser<Iterator> row;
};

我是这样使用的:

main() {
static const problem_parser<spirit::multi_pass<base_iterator_type> > p;
...
spirit::qi::phrase_parse(first, last ,
            p,
            qi::space,
            pb);
}

当然，qi::space 是我的问题，解决我的问题的一种方法是不使用船长，但phrase_parse 需要一个，然后我的解析器需要一个.

Of course, the qi::space is my problem, and a way to solve my problem would be to don't use a skipper, but phrase_parse requires one, and then my parser requires one.

我已经卡住了几个小时了...我认为这很明显是我误解了.

I'm stuck since some hours now... I think it's something obvious I have misunderstood.

感谢您的帮助.

推荐答案

总的来说，以下指令有助于在语法中阻止/切换跳过:

In general the following directives are helpful for inhibiting/switching skippers mid-grammar:

• qi::lexeme [ p ]
  禁止船长，例如如果您想确保在没有内部跳过的情况下解析标识符) - 另请参阅 no_skip 以进行比较

qi::raw [ p ]
像往常一样解析，包括跳过，但返回匹配源序列的原始迭代器范围(包括跳过的位置))

qi::raw [ p ]
which parses like always, including skips, but returns the raw iterator range of the matched source sequence (including the skipped positions)

qi::no_skip [ p ]
在没有预跳过的情况下禁止跳过(我已经创建了一个最小的例子来演示这里的区别:Boost Spirit lexeme vs no_skip)

qi::skip(s) [ p ]
用另一个船长 s 完全替换船长(注意你需要在这样的 skip[] 子句中使用适当声明的 qi::rule<> 实例)

qi::skip(s) [ p ]
which replaces the skipper by another skipper s altogether (note that you need to use appropriately declared qi::rule<> instances inside such a skip[] clause)

其中 p 是任何解析器表达式.

where p is any parser expression.

正如您已经知道的那样，您的问题可能是 qi::space 吃掉了所有 空格.我不可能知道你的语法有什么问题(因为你既没有显示完整的语法，也没有显示相关的输入).

Your problem, as you already know, might be that qi::space eats all whitespace. I can't possibly know what is wrong in your grammar (since you don't show either the full grammar, or relevant input).

因此，这就是我要写的.注意

Therefore, here's what I'd write. Note

• 使用qi::eol明确要求在特定位置换行
• 使用qi::blank作为船长(不包括eol)
• 为简洁起见，我合并了语法

• the use of qi::eol to explicitely require linebreaks at specific locations
• the use of qi::blank as a skipper (not including eol)
• for brevity I combined the grammars

代码:

#define BOOST_SPIRIT_DEBUG
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>

namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;

struct rowType {
    unsigned int number;
    std::list<unsigned int> list;
};

struct problemType {
    unsigned int ROW;
    std::vector<rowType> rows;
};

BOOST_FUSION_ADAPT_STRUCT(rowType, (unsigned int, number)(std::list<unsigned int>, list))
BOOST_FUSION_ADAPT_STRUCT(problemType, (unsigned int, ROW)(std::vector<rowType>, rows))

template<typename Iterator>
struct problem_parser : qi::grammar<Iterator,problemType(),qi::blank_type>
{
    problem_parser() : problem_parser::base_type(problem)
    {
        using namespace qi;
        list    = '[' >> -(int_ % ',') >> ']';
        row     = int_ >> list >> eol;
        problem = "ROW" >> int_ >> eol >> +row;

        BOOST_SPIRIT_DEBUG_NODES((problem)(row)(list));
    }

    qi::rule<Iterator, problemType()            , qi::blank_type> problem;
    qi::rule<Iterator, rowType()                , qi::blank_type> row;
    qi::rule<Iterator, std::list<unsigned int>(), qi::blank_type> list;
};

int main()
{
    const std::string input = 
        "ROW 1
"
        "2 [3, 4]
"
        "5 [6, 7]
";

    auto f = begin(input), l = end(input);

    problem_parser<std::string::const_iterator> p;
    problemType data;

    bool ok = qi::phrase_parse(f, l, p, qi::blank, data);

    if (ok) std::cout << "success
";
    else    std::cout << "failed
";

    if (f!=l)
        std::cout << "Remaining unparsed: '" << std::string(f,l) << "'
";
}

如果你真的不想要求换行:

If you really didn't want to require line breaks:

template<typename Iterator>
struct problem_parser : qi::grammar<Iterator,problemType(),qi::space_type>
{
    problem_parser() : problem_parser::base_type(problem)
    {
        using namespace qi;
        list    = '[' >> -(int_ % ',') >> ']';
        row     = int_ >> list;
        problem = "ROW" >> int_ >> +row;

        BOOST_SPIRIT_DEBUG_NODES((problem)(row)(list));
    }

    qi::rule<Iterator, problemType()            , qi::space_type> problem;
    qi::rule<Iterator, rowType()                , qi::space_type> row;
    qi::rule<Iterator, std::list<unsigned int>(), qi::space_type> list;
};

int main()
{
    const std::string input = 
        "ROW 1 " // NOTE whitespace, obviously required!
        "2 [3, 4]"
        "5 [6, 7]";

    auto f = begin(input), l = end(input);

    problem_parser<std::string::const_iterator> p;
    problemType data;

    bool ok = qi::phrase_parse(f, l, p, qi::space, data);

    if (ok) std::cout << "success
";
    else    std::cout << "failed
";

    if (f!=l)
        std::cout << "Remaining unparsed: '" << std::string(f,l) << "'
";
}

更新

回应评论:这里是一个片段，展示了如何从文件中读取输入.这已经过测试，对我来说效果很好:

Update

In response to the comment: here is a snippet that shows how to read the input from a file. This was tested and works fine for me:

std::ifstream ifs("input.txt"/*, std::ios::binary*/);
ifs.unsetf(std::ios::skipws);

boost::spirit::istream_iterator f(ifs), l;

problem_parser<boost::spirit::istream_iterator> p;

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