带有Boost Spirit的OBJ解析器-忽略评论 [英] OBJ Parser with Boost Spirit - Ignoring comments

问题描述

我正在尝试使用Boost Spirit库编写一个基本的OBJ文件加载器.尽管我使用标准std :: ifstreams使其工作，但我想知道是否可以使用内存映射文件对整个文件执行phrase_parse，因为它似乎提供了最佳性能，如

I'm trying to write a basic OBJ file loader using the Boost Spirit library. Although I got it working using the standard std::ifstreams, I'm wondering if it's possible to do a phrase_parse on the entire file using a memory mapped file, since it seems to provide the best performance as posted here.

我有以下代码，看起来似乎不错，但是当文件中有注释时，它就会中断.因此，我的问题是，如何使用Spririt忽略OBJ文件中以#"开头的注释?

I have the following code, which seems to work well, but it breaks when there is a comment in the file. So, my question is how do you ignore a comment that starts with a '#' in the OBJ file using Spririt?

struct vertex {
    double x, y, z;
};

BOOST_FUSION_ADAPT_STRUCT(
                          vertex,
                          (double, x)
                          (double, y)
                          (double, z)
                          )
std::vector<vertex> b_vertices         
boost::iostreams::mapped_file mmap(
                                           path,
                                           boost::iostreams::mapped_file::readonly);
        const char* f = mmap.const_data();
        const char* l = f + mmap.size();


        using namespace boost::spirit::qi;

      bool ok = phrase_parse(f,l,(("v" >> double_ >> double_ >> double_) |
                               ("vn" >> double_ >> double_>> double_)) % eol ,
                               blank, b_vertices);

当没有注释或任何其他数据(顶点/法线除外)时，上述代码可以很好地工作.但是，当存在不同类型的数据时，解析器将失败(应该如此)，我想知道是否有一种方法可以使它工作而又不重新解析每一行，因为它速度较慢(在我的测试中几乎是2.5倍) .谢谢！

The above code works well when there are no comments or any other data except vertices/normals. But when there is a different type of data the parser fails (as it should) and I'm wondering if there is a way to make it work without going back to parsing every line as it is slower (almost 2.5x in my tests). Thank you!

推荐答案

想到的最简单的方法是简单地使注释可跳过:

The simplest way that comes to mind is to simply make comments skippable:

bool ok = qi::phrase_parse(
        f,l,
         (
               ("v"  >> qi::double_ >> qi::double_ >> qi::double_) |
               ("vn" >> qi::double_ >> qi::double_ >> qi::double_)
          ) 
          % qi::eol,
        ('#' >> *(qi::char_ - qi::eol) >> qi::eol | qi::blank), b_vertices);

请注意，如果#出现在行内某处，这也会识别"注释.这可能很好(因为它将使解析失败，除非它是在其他有效输入行上尾随的注释).

Note that this also 'recognizes' comments if # appears somewhere inside the line. This is probably just fine (as it would make the parsing fail, unless it was a comment trailing on an otherwise valid input line).

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或者，使用一些凤凰魔法来处理注释行"，就像处理"vn"或"v"行一样.

Alternatively, use some phoenix magic to handle "comment lines" just as you handle a "vn" or "v" line.

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