使用Boost Spirit解析文本文件,同时跳过文本文件的大部分 [英] Using Boost Spirit to parse a text file while skipping large parts of it
问题描述
我有以下 std :: string
:
<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">
...
我想在所有出现<$ c $后提取单个整数c>标签A 或标签B
,并将它们放在相应的向量< int& a,b
。一个简单但不是优雅的方法是使用 find(label A)
和 find(label B)
和解析以先到为准。有没有一种简洁的方式使用精神表达?如何跳过标签A
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
您只需
omit [ eol >> *char_ - ("\nlabel A:") ] >> eol
示例: Live on Coliru
Example: Live On Coliru
还有 seek []
指令。以下等价于上述:
There's also the seek[]
directive in the repository. The following is equivalent to the above:
repo::seek [ eol >> &lit("int main") ]
以下是解析原始示例的示例: p>
Here's a sample that parses your original sample:
*repo::seek [ eol >> "label" >> char_("A-Z") >> ':' >> int_ ],
这将解析为 std :: vector< std :: pair< char,int>
This will parse into std::vector<std::pair<char, int> >
without anything else.
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";
}
注意:
-
seek
会显示匹配的属性,这是非常强大的:
seek
does expose the attribute matched, which is pretty powerful:
repo::seek [ eol >> "label" >> char_("ABCD") >> ':' ]
会吃标签, c>'A','B'
,'C'
c $ c>'D')作为属性。
will 'eat' the label, but expose the label letter ('A'
, 'B'
, 'C'
, or 'D'
) as the attribute.
跳过时的性能可能相当惊人,文档 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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