c++ - 使用 boost spirit 拆分字符串

Question

这是个好主意吗？出于某种原因，我认为它应该比 boost 的分词器或拆分器更快。然而大多数时候我都停留在 boost::spirit::compile

template <typename Iterator>
struct ValueList : bsq::grammar<Iterator, std::vector<std::string>()>
{
    ValueList(const std::string& sep, bool isCaseSensitive) : ValueList::base_type(query)
    {
        if(isCaseSensitive)
        {
            query = value >> *(sep >> value);
            value = *(bsq::char_ - sep);
        }
        else
        {
            auto separator = bsq::no_case[sep];
            query = value >> *(separator >> value);
            value = *(bsq::char_ - separator);
        }
    }
    bsq::rule<Iterator, std::vector<std::string>()> query;
    bsq::rule<Iterator, std::string()> value;
};

inline bool Split(std::vector<std::string>& result, const std::string& buffer, const std::string& separator,
                  bool isCaseSensitive)
{
    result.clear();
    ValueList<std::string::const_iterator> parser(separator, isCaseSensitive);
    auto itBeg = buffer.begin();
    auto itEnd = buffer.end();
    if(!(bsq::parse(itBeg, itEnd, parser, result) && (itBeg == itEnd)))
        result.push_back(buffer);
    return true;
}

我已经如上所示实现了它。我的代码有什么问题？或者只是因为分隔符是在运行时定义的，所以重新编译是不可避免的？

编辑001:在 CoLiRu 上使用 boost::split 和带有标记器的原始 imp 的可能实现的示例和比较看起来 coliru 现在倒闭了。在任何情况下，这些都是在带有分隔符“|”的字符串“2lkhj309|ioperwkl|20sdf39i|rjjdsf|klsdjf230o|kx23904iep2|xp39f4p2|xlmq2i3219”上运行 1M 的结果

8000000 splits in 1081ms.
8000000 splits in 1169ms.
8000000splits in 2663ms.

第一个用于分词器，第二个用于 boost::split，第三个用于 boost::spirit

Answer 1

首先，不同的版本不会做同样的事情:

• 特别是 token 压缩的行为不同(我为 boost::split 修复了它，但它似乎不是 boost::tokenizer 的功能)<
• 分隔符在 Spirit 版本中被视为字符串文字而不是字符集(已修复)

是的，对于动态分隔符，重新编译是不可避免的。但是不，这不是瓶颈(其他方法也有动态分隔符):

---

我做了一些优化。时间:

• Coliru clang++ :

  8000000 original (boost::tokenizer) rate: 2.84257μs
  10000000 possible (boost::split) rate: 3.09941μs
  10000000 spirit (dynamic version) rate: 1.45456μs
  10000000 spirit (direct version, avoid type erasure) rate: 1.25588μs
  
  next step:
  10000000 spirit (precompiled sep) rate: 1.18059μs
  

• Coliru g++

  8000000 original (boost::tokenizer) rate: 2.92805μs
  10000000 possible (boost::split) rate: 2.75442μs
  10000000 spirit (dynamic version) rate: 1.32821μs
  10000000 spirit (direct version, avoid type erasure) rate: 1.10712μs
  
  next step:
  10000000 spirit (precompiled sep) rate: 1.0791μs
  

• 本地系统 g++:

  sehe@desktop:/tmp$ time ./test
  8000000 original (boost::tokenizer) rate: 1.80061μs
  10000000 possible (boost::split) rate: 1.29754μs
  10000000 spirit (dynamic version) rate: 0.607789μs
  10000000 spirit (direct version, avoid type erasure) rate: 0.488087μs
  
  next step:
  10000000 spirit (precompiled sep) rate: 0.498769μs
  

如您所见，Spirit 方法不需要更慢。我采取了哪些步骤？ http://paste.ubuntu.com/11001344/

• 将基准重构为显示速率(无变化)3.523μs
• 为调用者选择 case_insensitivity(如果需要，只需使用 no_case[char_(delimiter)])2.742μs。
• 消除 value 子规则(由于类型删除的非终端规则，减少了复制和动态分派(dispatch))2.579μs。

• 制作分隔符字符集而不是字符串文字:2.693μs。

  see intermediate version on coliru. (I recommend the code below, it's much more cleaned up)

• 使用 qi::raw[] 而不是 std::string 合成属性(避免复制!)0.624072μs

• 消除所有非终结符(即类型删除；参见 spirit_direct 实现)速率:0.491011μs

现在很明显，所有的实现都将受益于不每次都“编译”分隔符。我没有对所有方法都这样做，但为了好玩，让我们为 Spirit 版本这样做:

• 使用硬编码的“|”定界符0.455269μs//固定定界符

---

完整 list :

Live On Coliru

#include <boost/algorithm/string.hpp>
#include <boost/tokenizer.hpp>
#include <boost/spirit/include/qi.hpp>

#include <vector>
#include <string>
#include <chrono>
#include <iostream>

void original(std::vector<std::string>& result, const std::string& input, const std::string& delimiter)
{
    result.clear();
    boost::char_separator<char> sep(delimiter.c_str());
    boost::tokenizer<boost::char_separator<char>, std::string::const_iterator, std::string> tok(input, sep);

    for (const auto& token : tok)
    {
        result.push_back(token);
    }
}

void possible(std::vector<std::string>& result, const std::string& input, const std::string& delimiter)
{
    result.clear();
    boost::split(result, input, boost::is_any_of(delimiter), boost::algorithm::token_compress_off);
}

namespace bsq = boost::spirit::qi;

void spirit_direct(std::vector<std::string>& result, const std::string& input, char const* delimiter)
{
    result.clear();
    using namespace bsq;
    if (!parse(input.begin(), input.end(), raw[*(char_ - char_(delimiter))] % char_(delimiter), result))
        result.push_back(input);
}

namespace detail {
    template <typename Sep> bsq::rule<std::string::const_iterator, std::vector<std::string>()>
        make_spirit_parser(Sep const& sep) 
        {
            using namespace bsq;
            return raw[*(char_ - sep)] % sep;
        }

    static const auto precompiled_pipes = make_spirit_parser('|');
}

void spirit(std::vector<std::string>& result, const std::string& input, char const* delimiter)
{
    result.clear();
    if (!bsq::parse(input.begin(), input.end(), detail::make_spirit_parser(bsq::char_(delimiter)), result))
        result.push_back(input);
}

void spirit_pipes(std::vector<std::string>& result, const std::string& input)
{
    result.clear();
    if (!bsq::parse(input.begin(), input.end(), detail::precompiled_pipes, result))
        result.push_back(input);
}

template <typename F> void bench(std::string const& caption, F approach) {
    size_t const iterations = 1000000;
    using namespace std::chrono;
    using C = high_resolution_clock;

    auto start = C::now();

    size_t count = 0;
    for (auto i = 0U; i < iterations; ++i) {
        count += approach();
    }

    auto us = duration_cast<std::chrono::microseconds>(C::now() - start).count();
    std::cout << count << " " << caption << " rate: " << (1.*us/iterations) << "μs\n";
}

int main()
{
    std::string const input = "2309|ioperwkl|2039i|rjjdsf|klsdjf230o|kx23904iep2|xp,39,4p2|xlmq2i3219||";
    auto separator = "|";

    std::vector<std::string> result;

    bench("original (boost::tokenizer)", [&] {
            original(result, input, separator);
            return result.size();
        });
    bench("possible (boost::split)", [&] {
            possible(result, input, separator);
            return result.size();
        });
    bench("spirit (dynamic version)", [&] {
            spirit(result, input, separator);
            return result.size();
        });
    bench("spirit (direct version, avoid type erasure)", [&] {
            spirit_direct(result, input, separator);
            return result.size();
        });

    std::cout << "\nnext step:\n";
    bench("spirit (precompiled sep)", [&] {
            spirit_pipes(result, input);
            return result.size();
        });
}