如何在不跳过 eol 的情况下使用船长 ascii::space?

2021-12-24 00:00:00 parsing c++ boost boost-spirit boost-spirit-qi

我必须使用 boost::spirit 进行解析，我想使用phrase_parse 函数:

I have to use boost::spirit for parsing, and I want use phrase_parse function :

qi::phrase_parse(str.begin(), str.end(), grammar, ascii::space - qi::eol);

但是我的编译器不允许第四项(ascii::space - qi::eol).如何在不跳过 eol 的情况下使用船长 ascii::space ?

But the fourth term (ascii::space - qi::eol), isnt allowed by my compiler. How can I use the skipper ascii::space WITHOUT skipping eol ?

推荐答案

最简单的答案是

qi::phrase_parse(str.begin(), str.end(), grammar, ascii::blank);

当然，这也取决于你的语法:如果它需要一个特定的船长类，你可能需要改变它.请参阅下面的通用处理方式(尽管您可以只为只接受 的语法指定 qi::blank_typeqi::blank).

Of course, it depends on your grammar too: if it expects a specific skipper class you might need to change that. See below for a generic way to handle that (although you could just specify qi::blank_type for a Grammar that should only accept qi::blank).

该示例也处理任意跳过程序.

The sample handles arbitrary skippers too.

Spirit 有几个指令会影响船长的使用:??

Spirit has several directives that influence the use of skippers:

  • qi::lexeme

将解析子表达式而不考虑船长(对于例如语法中的字符串文字很有用)

will parse the sub-expression regardless of skipper (useful for e.g. string literals in a grammar)

qi::raw

将返回原始源迭代器范围，这意味着跳过的输入将包含在结果中

will return the raw source iterator range, meaning that skipped input will be included in the result

qi::no_skip, qi::skip

可用于显式更改用于子表达式的船长类型

can be used to explicitely change the type of skipper used for the subexpression

Boost Spirit 网站上有一篇关于此类内容的好文章

The Boost Spirit site has a nice article about things like this

  • 解析船长和跳过解析器
#include <boost/spirit/include/qi.hpp>

namespace qi = boost::spirit::qi;

template <typename It, typename Skipper>
    struct parser : qi::grammar<It, Skipper>
{
    parser() : parser::base_type(start)
    {
        start = *qi::int_;
    }

  private:
    qi::rule<It, Skipper> start;
};

template <typename C, typename Skipper>
    void doParse(const C& input, const Skipper& skipper)
{
    auto f(std::begin(input)), l(std::end(input));

    parser<decltype(f), Skipper> p;
    bool ok = qi::phrase_parse(f,l,p,skipper);

    if (ok)   
        std::cout << "parse success
";
}

int main()
{
    const std::string input = "1 2 3 4";
    doParse(input, qi::blank);
    doParse(input, qi::space);
    doParse(input, ~qi::char_("0-9"));
}

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