使用Boost精神解析一个文本文件，而跳过它的大部分 [英] Using Boost Spirit to parse a text file while skipping large parts of it

问题描述

我有如下的的std ::字符串：

<lots of text not including "label A" or "label B">    
label A: 34
<lots of text not including "label A" or "label B">
label B: 45
<lots of text not including "label A" or "label B">
...

我要提取下面的所有出现单一的整体数字标签的或标签B ，并放置在相应的矢量＆lt;＆INT GT; A，B 。这样做的一个简单的，但不是优雅的方式是使用找到（标签的）和找到（标签B）和解析以先到为准。有前$ P $使用精神pssing它简洁的方式？你如何跳过一切，但标签的或标签B ？

I want extract single integral numbers following all occurrences of label A or label B and place them in corresponding vector<int> a, b. A simple, but not elegant way of doing it is using find("label A") and find("label B") and parsing whichever is first. Is there a succinct way of expressing it using Spirit? How do you skip everything but label A or label B?

推荐答案

您可以只

omit [ eol >> *char_ - ("\nlabel A:") ] >> eol

例如： 住在Coliru

Example: Live On Coliru

还有资源库中的寻求[] 指令。以下是相当于上面

There's also the seek[] directive in the repository. The following is equivalent to the above:

 repo::seek [ eol >> &lit("int main") ] 

下面是它分析你的原始样品的样品：

Here's a sample that parses your original sample:

*repo::seek [ eol >> "label" >> char_("A-Z") >> ':' >> int_ ],

这将解析成的std ::矢量＆lt;的std ::对＆LT;焦炭，INT＆GT;方式＆gt; 没有别的

在Coliru太

On Coliru Too:

#if 0
<lots of text not including "label A" or "label B">    
label A: 34
<lots of text not including "label A" or "label B">
label B: 45
<lots of text not including "label A" or "label B">
...
#endif
#include <boost/fusion/adapted/std_pair.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/repository/include/qi_seek.hpp>
#include <fstream>

namespace qi   = boost::spirit::qi;
namespace repo = boost::spirit::repository::qi;

int main()
{
    std::ifstream ifs("main.cpp");
    ifs >> std::noskipws;

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

    std::vector<std::pair<char, int> > parsed;
    using namespace qi;
    bool ok = phrase_parse(
            f, l, 
            *repo::seek [ eol >> "label" >> char_("A-Z") >> ':' >> int_ ],
            blank,
            parsed
        );

    if (ok)
    {
        std::cout << "Found:\n";
        for (auto& p : parsed)
            std::cout << "'" << p.first << "' has value " << p.second << "\n";
    }
    else
        std::cout << "Fail at: '" << std::string(f,l) << "'\n";
}

注：

• 征求并揭露相匹配的属性，它是pretty强大：

• seek does expose the attribute matched, which is pretty powerful:

repo::seek [ eol >> "label" >> char_("ABCD") >> ':' ] 

将'吃'的标签，但暴露的标签号（'A'，'B'， 'C'或'D'）的属性。

性能跳绳可以pretty令人惊讶的时候，阅读文档<一个在警告href=\"http://www.boost.org/doc/libs/1_55_0/libs/spirit/repository/doc/html/spirit_repository/qi_components/directives/seek.html\" rel=\"nofollow\">http://www.boost.org/doc/libs/1_55_0/libs/spirit/repository/doc/html/spirit_repository/qi_components/directives/seek.html

Performance when skipping can be pretty surprising, read the warning in the documentation http://www.boost.org/doc/libs/1_55_0/libs/spirit/repository/doc/html/spirit_repository/qi_components/directives/seek.html

输出为

Found:
'A' has value 34
'B' has value 45

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