使用 boost::program_options 解析文本文件是个好主意吗？

Question

我必须处理大量具有明确定义的语法和语义的文件，例如：

• 第一行是带有特殊信息的标题
• 其他行在行首包含一个键值，告诉您如何解析和处理该行的内容
• 如果有评论，则以给定的标记开头
• 等等等等……

现在boost::program_options，据我所知，做的工作几乎相同，但我只关心导入这些文本文件的内容，中间没有任何额外的工作，只需解析它并将其存储在我的数据结构。

对我来说关键的一步是我希望能够通过以下方式进行解析：

• 正则表达式，因为我需要检测不同的语义，我真的无法想象另一种方法来做到这一点
• 错误检查（文件损坏，即使在解析整个文件后，密钥也不匹配，等等......）

那么，我可以使用这个库来完成这项工作吗？还有更实用的方法吗？

Answer 1

好的，精神语法的起点

_Name    = "newmtl" >> lexeme [ +graph ];
_Ns      = "Ns"     >> double_;
_Ka      = "Ka"     >> double_ >> double_ >> double_;
_Kd      = "Kd"     >> double_ >> double_ >> double_;
_Ks      = "Ks"     >> double_ >> double_ >> double_;
_d       = "d"      >> double_;
_illum  %= "illum"  >> qi::int_ [ _pass = (_1>=0) && (_1<=10) ];

comment  = '#' >> *(char_ - eol);

statement=
         comment
       | _Ns    [ bind(&material::_Ns, _r1) = _1 ]
       | _Ka    [ bind(&material::_Ka, _r1) = _1 ]
       | _Kd    [ bind(&material::_Kd, _r1) = _1 ]
       | _Ks    [ bind(&material::_Ks, _r1) = _1 ]
       | _d     [ bind(&material::_d,  _r1) = _1 ]
       | _illum [ bind(&material::_illum, _r1) = _1 ]
       ;

_material = -comment % eol
        >> _Name [ bind(&material::_Name, _val) = _1 ] >> eol
        >> -statement(_val) % eol;

start = _material % -eol;

我仅从您的示例文件中实现了 MTL 文件子集语法。

注意：这是一个相当简单的语法。但是，你知道，第一件事。实际上我可能会考虑使用the keyword list parser from the spirit repository。它具有“要求”不同“字段类型”出现一定次数的功能。

注意： Spirit Karma（以及大约 50 行其他代码）仅用于演示目的。

以下内容为untitled.mtl

# Blender MTL File: 'None'
# Material Count: 2

newmtl None
Ns 0
Ka 0.000000 0.000000 0.000000
Kd 0.8 0.8 0.8
Ks 0.8 0.8 0.8
d 1
illum 2
# Added just for testing:

newmtl Demo
Ns 1
Ks 0.9 0.9 0.9
d 42
illum 7

输出读取

phrase_parse -> true
remaining input: ''
void dump(const T&) [with T = std::vector<blender::mtl::material>]
-----
material {
    Ns:0
    Ka:{r:0,g:0,b:0}
    Kd:{r:0.8,g:0.8,b:0.8}
    Ks:{r:0.8,g:0.8,b:0.8}
    d:1
    illum:2(Highlight on)
}
material {
    Ns:1
    Ka:(unspecified)
    Kd:(unspecified)
    Ks:{r:0.9,g:0.9,b:0.9}
    d:42
    illum:7(Transparency: Refraction on/Reflection: Fresnel on and Ray trace on)
}
-----

这是列表

#define BOOST_SPIRIT_USE_PHOENIX_V3
#define BOOST_SPIRIT_DEBUG

#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp> // for debug output/streaming
#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>

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

namespace wavefront { namespace obj
{
} }

namespace blender { namespace mtl // material?
{
    struct Ns { int exponent; }; // specular exponent
    struct Reflectivity { double r, g, b; };

    using Name = std::string;
    using Ka   = Reflectivity;
    using Kd   = Reflectivity;
    using Ks   = Reflectivity;

    using dissolve_factor = double;
    enum class illumination_model {
            color,          // 0     Color on and Ambient off
            color_ambient,  // 1     Color on and Ambient on
            highlight,      // 2     Highlight on
            reflection_ray, // 3     Reflection on and Ray trace on
            glass_ray,      // 4     Transparency: Glass on
                            //       Reflection: Ray trace on
            fresnel_ray,    // 5     Reflection: Fresnel on and Ray trace on
            refract_ray,    // 6     Transparency: Refraction on
                            //       Reflection: Fresnel off and Ray trace on
            refract_ray_fresnel,// 7 Transparency: Refraction on
                            //       Reflection: Fresnel on and Ray trace on
            reflection,     // 8     Reflection on and Ray trace off
            glass,          // 9     Transparency: Glass on
                            //       Reflection: Ray trace off
            shadow_invis,   // 10    Casts shadows onto invisible surfaces
    };

    struct material
    {
        Name                                _Name;
        boost::optional<Ns>                 _Ns;
        boost::optional<Reflectivity>       _Ka;
        boost::optional<Reflectivity>       _Kd;
        boost::optional<Reflectivity>       _Ks;
        boost::optional<dissolve_factor>    _d;
        boost::optional<illumination_model> _illum;
    };

    using mtl_file = std::vector<material>;

    ///////////////////////////////////////////////////////////////////////
    // Debug output helpers
    std::ostream& operator<<(std::ostream& os, blender::mtl::illumination_model o)
    {
        using blender::mtl::illumination_model;
        switch(o)
        {
            case illumination_model::color:               return os << "0(Color on and Ambient off)";
            case illumination_model::color_ambient:       return os << "1(Color on and Ambient on)";
            case illumination_model::highlight:           return os << "2(Highlight on)";
            case illumination_model::reflection_ray:      return os << "3(Reflection on and Ray trace on)";
            case illumination_model::glass_ray:           return os << "4(Transparency: Glass on/Reflection: Ray trace on)";
            case illumination_model::fresnel_ray:         return os << "5(Reflection: Fresnel on and Ray trace on)";
            case illumination_model::refract_ray:         return os << "6(Transparency: Refraction on/Reflection: Fresnel off and Ray trace on)";
            case illumination_model::refract_ray_fresnel: return os << "7(Transparency: Refraction on/Reflection: Fresnel on and Ray trace on)";
            case illumination_model::reflection:          return os << "8(Reflection on and Ray trace off)";
            case illumination_model::glass:               return os << "9(Transparency: Glass on/Reflection: Ray trace off)";
            case illumination_model::shadow_invis:        return os << "10(Casts shadows onto invisible surfaces)";
            default: return os << "ILLEGAL VALUE";
        }
    }

    std::ostream& operator<<(std::ostream& os, blender::mtl::Reflectivity const& o)
    {
        return os << "{r:" << o.r << ",g:" << o.g << ",b:" << o.b << "}";
    }

    std::ostream& operator<<(std::ostream& os, blender::mtl::material const& o)
    {
        using namespace boost::spirit::karma;
        return os << format("material {"
                "\n\tNs:"    << (auto_  | "(unspecified)")
                << "\n\tKa:"    << (stream | "(unspecified)")
                << "\n\tKd:"    << (stream | "(unspecified)")
                << "\n\tKs:"    << (stream | "(unspecified)")
                << "\n\td:"     << (stream | "(unspecified)")
                << "\n\tillum:" << (stream | "(unspecified)")
                << "\n}", o);
    }
} }

BOOST_FUSION_ADAPT_STRUCT(blender::mtl::Reflectivity,(double, r)(double, g)(double, b))
BOOST_FUSION_ADAPT_STRUCT(blender::mtl::Ns, (int, exponent))
BOOST_FUSION_ADAPT_STRUCT(blender::mtl::material,
        (boost::optional<blender::mtl::Ns>, _Ns)
        (boost::optional<blender::mtl::Ka>, _Ka)
        (boost::optional<blender::mtl::Kd>, _Kd)
        (boost::optional<blender::mtl::Ks>, _Ks)
        (boost::optional<blender::mtl::dissolve_factor>, _d)
        (boost::optional<blender::mtl::illumination_model>, _illum))

namespace blender { namespace mtl { namespace parsing
{
    template <typename It>
        struct grammar : qi::grammar<It, qi::blank_type, mtl_file()>
    {
        template <typename T=qi::unused_type> using rule = qi::rule<It, qi::blank_type, T>;

        rule<Name()>               _Name;
        rule<Ns()>                 _Ns;
        rule<Reflectivity()>       _Ka;
        rule<Reflectivity()>       _Kd;
        rule<Reflectivity()>       _Ks;
        rule<dissolve_factor()>    _d;
        rule<illumination_model()> _illum;

        rule<mtl_file()> start;
        rule<material()> _material;
        rule<void(material&)> statement;
        rule<> comment;

        grammar() : grammar::base_type(start)
        {
            using namespace qi;
            using phx::bind;
            using blender::mtl::material;

            _Name    = "newmtl" >> lexeme [ +graph ];
            _Ns      = "Ns"     >> double_;
            _Ka      = "Ka"     >> double_ >> double_ >> double_;
            _Kd      = "Kd"     >> double_ >> double_ >> double_;
            _Ks      = "Ks"     >> double_ >> double_ >> double_;
            _d       = "d"      >> double_;
            _illum  %= "illum"  >> qi::int_ [ _pass = (_1>=0) && (_1<=10) ];

            comment  = '#' >> *(char_ - eol);

            statement=
                    comment
                | _Ns    [ bind(&material::_Ns, _r1) = _1 ]
                | _Ka    [ bind(&material::_Ka, _r1) = _1 ]
                | _Kd    [ bind(&material::_Kd, _r1) = _1 ]
                | _Ks    [ bind(&material::_Ks, _r1) = _1 ]
                | _d     [ bind(&material::_d,  _r1) = _1 ]
                | _illum [ bind(&material::_illum, _r1) = _1 ]
                ;

            _material = -comment % eol
                    >> _Name [ bind(&material::_Name, _val) = _1 ] >> eol
                    >> -statement(_val) % eol;

            start = _material % -eol;

            BOOST_SPIRIT_DEBUG_NODES(
                    (start)
                    (statement)
                    (_material)
                    (_Name) (_Ns) (_Ka) (_Kd) (_Ks) (_d) (_illum)
                    (comment))
        }

};

} } }

#include <fstream>

template <typename T>
void dump(T const& data)
{
    using namespace boost::spirit::karma;
    std::cout << __PRETTY_FUNCTION__
        << "\n-----\n"
        << format(stream % eol, data)
        << "\n-----\n";
}

void testMtl(const char* const fname)
{
    std::ifstream mtl(fname, std::ios::binary);
    mtl.unsetf(std::ios::skipws);
    boost::spirit::istream_iterator f(mtl), l;

    using namespace blender::mtl::parsing;
    static const grammar<decltype(f)> p;

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

    std::cout << "phrase_parse -> " << std::boolalpha << ok << "\n";
    std::cout << "remaining input: '" << std::string(f,l) << "'\n";

    dump(data);
}

int main()
{
    testMtl("untitled.mtl");
}

Answer 2

是的，至少如果您将配置文件像键值对映射一样简单（类似于简单的 .ini）。

来自documentation：

program_options 库允许程序开发人员获得 程序选项，即来自用户的（名称，值）对，通过 命令行和配置文件等常规方法。

...

可以从任何地方读取选项。迟早是命令行 对您的用户来说还不够，您需要 配置文件 或 甚至可能是环境变量。这些可以不加 您付出了巨大的努力。

详情请见"multiple sources" sample。

但是，如果您需要（或将来可能需要）更复杂的配置文件（例如 XML、JSON 或二进制文件），则值得使用独立库。

Answer 3

这很可能，但不一定方便。如果你想解析任何你想使用解析器的东西——你是使用现有的还是自己写的取决于你在解析什么。

如果无法使用任何现有工具解析您的格式，那么只需编写您自己的解析器。您可以将 lex/flex/flex++ 与 yacc/bison/bison++ 或 boost::spirit 一起使用。

我认为从长远来看，学习维护自己的解析器会比强制调整 boost::program_options 配置更有用，但不如使用一些已经满足您需求的现有解析器方便。