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27
4
我想提出一个让我陷入困境的主题，并提出了一个关于齐::符号。
这一切都始于我查看新的野兽图书馆并阅读 atutorial example
它以一个从 http 路径猜测 mime 类型的函数开始扩展。我开始仔细观察，看到了这个:
auto const ext = [&path]
{
auto const pos = path.rfind(".");
if(pos == boost::beast::string_view::npos)
return boost::beast::string_view{};
return path.substr(pos);
}();
我花了一段时间才弄清楚这是一个 IIFE在 C++ 风格中，用于初始化 ext，同时声明它为常量。
无论如何，我开始测试这是否会产生任何性能差异将证明可怕的可读性与直接实现相比是合理的。
这样做我开始怀疑这在齐::符号。所以我想出了两个替代实现:
#include <boost/smart_ptr/scoped_array.hpp>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/mean.hpp>
#include <boost/accumulators/statistics/moment.hpp>
#include <boost/chrono.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/qi_parse.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/vector.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/algorithm/string.hpp>
#include <boost/assign.hpp>
#include <iostream>
#include <string>
#include <vector>
#include <random>
using namespace boost::accumulators;
typedef boost::chrono::duration<long long, boost::micro> microseconds;
namespace qi = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace ascii = qi::ascii;
namespace phx = boost::phoenix;
const std::map<const std::string, const std::string> mime_exts = {
{ ".htm", "text/html" },
{ ".html", "text/html" },
{ ".php", "text/html" },
{ ".css", "text/css" },
{ ".js", "application/javascript" },
{ ".json", "application/json" },
{ ".xml", "application/xml" },
{ ".swf", "application/x-shockwave-flash" },
{ ".flv", "video/x-flv" },
{ ".png", "image/png" },
{ ".jpe", "image/jpeg" },
{ ".jpeg", "image/jpeg" },
{ ".jpg", "image/jpeg" },
{ ".gif", "image/gif" },
{ ".bmp", "image/bmp" },
{ ".ico", "image/vnd.microsoft.icon" },
{ ".tif", "image/tiff" },
{ ".tiff", "image/tiff" },
{ ".svg", "image/svg+xml"},
{ ".svgz", "image/svg+xml"}
};
const char *mime_literals[] = {
"text/html",
"text/css",
"text/plain",
"application/javascript",
"application/json",
"application/xml",
"application/x-shockwave-flash",
"video/x-flv",
"image/png",
"image/jpeg",
"image/gif",
"image/bmp",
"image/vnd.microsoft.icon",
"image/tiff",
"image/svg+xml"
};
template <typename Iterator>
struct mimetype_matching_parser : qi::grammar<Iterator, unsigned int()> {
mimetype_matching_parser() : mimetype_matching_parser::base_type(m_start, "mimetype_matching_parser") {
m_mime_extensions.add
(".htm", 0)
(".html", 0)
(".php", 0)
(".css", 1)
(".txt", 2)
(".js", 3)
(".json", 4)
(".xml", 5)
(".swf", 6)
(".flv", 7)
(".png", 8)
(".jpe", 9)
(".jpeg", 9)
(".jpg", 9)
(".gif", 10)
(".bmp", 11)
(".ico", 12)
(".tiff", 13)
(".tif", 13)
(".svg", 14)
(".svgz", 14)
;
using qi::no_case;
m_start %= no_case[m_mime_extensions] >> qi::eoi;
}
qi::symbols<char, unsigned int> m_mime_extensions;
qi::rule<Iterator, unsigned int()> m_start;
};
std::string mime_extension(const std::string &n_path) {
// First locate the extension itself
const std::size_t last_dot = n_path.rfind(".");
if (last_dot == std::string::npos) {
return "application/text";
}
// and now pipe the extension into a qi symbols parser.
// I don't know if this is any faster than a more trivial algorithm::ends_with
// approach but I guess it won't be any slower
const mimetype_matching_parser<std::string::const_iterator> p;
unsigned int result;
std::string::const_iterator begin = n_path.begin() + last_dot;
const std::string::const_iterator end = n_path.end();
try {
if (qi::parse(begin, end, p, result) && (begin == end)) {
return mime_literals[result];
} else {
return "application/text";
}
} catch (const std::exception &) { // asio throws on invalid parse
return "application/text";
}
}
std::string mime_extension2(const std::string &n_path) {
using boost::algorithm::iequals;
auto const ext = [&n_path] {
auto const pos = n_path.rfind(".");
if (pos == std::string::npos)
return std::string{};
return n_path.substr(pos);
}();
// const std::size_t pos = n_path.rfind(".");
// if (pos == std::string::npos) {
// return std::string{};
// }
// const std::string ext = n_path.substr(pos);
if (iequals(ext, ".htm")) return "text/html";
if (iequals(ext, ".html")) return "text/html";
if (iequals(ext, ".php")) return "text/html";
if (iequals(ext, ".css")) return "text/css";
if (iequals(ext, ".txt")) return "text/plain";
if (iequals(ext, ".js")) return "application/javascript";
if (iequals(ext, ".json")) return "application/json";
if (iequals(ext, ".xml")) return "application/xml";
if (iequals(ext, ".swf")) return "application/x-shockwave-flash";
if (iequals(ext, ".flv")) return "video/x-flv";
if (iequals(ext, ".png")) return "image/png";
if (iequals(ext, ".jpe")) return "image/jpeg";
if (iequals(ext, ".jpeg")) return "image/jpeg";
if (iequals(ext, ".jpg")) return "image/jpeg";
if (iequals(ext, ".gif")) return "image/gif";
if (iequals(ext, ".bmp")) return "image/bmp";
if (iequals(ext, ".ico")) return "image/vnd.microsoft.icon";
if (iequals(ext, ".tiff")) return "image/tiff";
if (iequals(ext, ".tif")) return "image/tiff";
if (iequals(ext, ".svg")) return "image/svg+xml";
if (iequals(ext, ".svgz")) return "image/svg+xml";
return "application/text";
}
std::string mime_extension3(const std::string &n_path) {
using boost::algorithm::iequals;
auto ext = [&n_path] {
auto const pos = n_path.rfind(".");
if (pos == std::string::npos) {
return std::string{};
} else {
return n_path.substr(pos);
}
}();
boost::algorithm::to_lower(ext);
const std::map<const std::string, const std::string>::const_iterator i = mime_exts.find(ext);
if (i != mime_exts.cend()) {
return i->second;
} else {
return "application/text";
}
}
const std::string samples[] = {
"test.txt",
"test.html",
"longer/test.tiff",
"www.webSite.de/ico.ico",
"www.websIte.de/longEr/path/ico.bmp",
"www.TEST.com/longer/path/ico.svg",
"googlecom/shoRT/path/index.HTM",
"googlecom/bild.jpg",
"WWW.FLASH.COM/app.swf",
"WWW.FLASH.COM/BILD.GIF"
};
int test_qi_impl() {
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 10);
const std::string sample = samples[dis(gen)];
const std::string result = mime_extension(sample);
int ret = dis(gen);
for (const char &c : result) { ret += c; }
return ret;
}
int test_lambda_impl() {
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 10);
const std::string sample = samples[dis(gen)];
const std::string result = mime_extension2(sample);
int ret = dis(gen);
for (const char &c : result) { ret += c; }
return ret;
}
int test_map_impl() {
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 10);
const std::string sample = samples[dis(gen)];
const std::string result = mime_extension3(sample);
int ret = dis(gen);
for (const char &c : result) { ret += c; }
return ret;
}
int main(int argc, char **argv) {
const unsigned int loops = 100000;
accumulator_set<boost::chrono::high_resolution_clock::duration, features<tag::mean> > times_qi;
accumulator_set<boost::chrono::high_resolution_clock::duration, features<tag::mean> > times_lambda;
accumulator_set<boost::chrono::high_resolution_clock::duration, features<tag::mean> > times_map;
std::cout << "Measure execution times for " << loops << " lambda runs" << std::endl;
for (unsigned int i = 0; i < loops; i++) {
boost::chrono::high_resolution_clock::time_point start = boost::chrono::high_resolution_clock::now();
test_lambda_impl();
boost::chrono::high_resolution_clock::time_point end = boost::chrono::high_resolution_clock::now();
times_lambda(end - start);
}
std::cout << "Measure execution times for " << loops << " qi runs" << std::endl;
for (unsigned int i = 0; i < loops; i++) {
boost::chrono::high_resolution_clock::time_point start = boost::chrono::high_resolution_clock::now();
test_qi_impl();
boost::chrono::high_resolution_clock::time_point end = boost::chrono::high_resolution_clock::now();
times_qi(end - start);
}
std::cout << "Measure execution times for " << loops << " map runs" << std::endl;
for (unsigned int i = 0; i < loops; i++) {
boost::chrono::high_resolution_clock::time_point start = boost::chrono::high_resolution_clock::now();
test_map_impl();
boost::chrono::high_resolution_clock::time_point end = boost::chrono::high_resolution_clock::now();
times_map(end - start);
}
std::cout << "Lambda runs took " << mean(times_lambda) << std::endl;
std::cout << "Qi runs took " << mean(times_qi) << std::endl;
std::cout << "Map runs took " << mean(times_map) << std::endl;
return EXIT_SUCCESS;
}
令我惊讶的是，lambda 确实很重要(一点点)。让我吃惊的是更重要的是，qi 的实现速度要慢得多。
Measure execution times for 100000 lambda runs
Measure execution times for 100000 qi runs
Measure execution times for 100000 map runs
Lambda runs took 12443 nanoseconds
Qi runs took 15311 nanoseconds
Map runs took 10466 nanoseconds
首先，我使用的是这样的符号
template <typename Iterator>
struct mimetype_matching_parser : qi::grammar<Iterator, std::string()> {
mimetype_matching_parser() : mimetype_matching_parser::base_type(m_start,
"mimetype_matching_parser") {
m_mime_extensions.add
(".htm", "text/html")
(".html", "text/html")
(".php", "text/html")
(".css", "text/css")
(".svg", "whatever...")
;
using qi::no_case;
m_start %= no_case[m_mime_extensions] >> qi::eoi;
}
qi::symbols<char, std::string> m_mime_extensions;
qi::rule<Iterator, std::string()> m_start;
};
直接返回字符串作为属性。有同事指出这是一个额外的 std::string 拷贝所以我改变了它所以它只返回一个索引到静态字符数组:
const char *mime_literals[] = {
"text/html",
"text/css",
"text/plain",
// ... and so forth
};
template <typename Iterator>
struct mimetype_matching_parser : qi::grammar<Iterator, unsigned int()> {
mimetype_matching_parser() : mimetype_matching_parser::base_type(m_start, "mimetype_matching_parser")
{
m_mime_extensions.add
(".htm",0)
(".html",0)
(".php",0)
(".css",1)
(".svg",... etc.
;
using qi::no_case;
m_start %= no_case[m_mime_extensions] >> qi::eoi;
}
qi::symbols<char, unsigned int> m_mime_extensions;
qi::rule<Iterator, unsigned int()> m_start;
};
这有点快，但真的不值得一提。
在我的笔记本电脑上，在 Release模式下，我得到: - Beast Tutorial (Lambda) 实现平均每次运行 6200 纳秒。 - Qi 实现平均耗时约 7100 纳秒。
现在，这将是我的第一个问题:这是为什么？
“野兽”实现让我印象深刻，因为它经历了所有子字符串，每次都调用 iequals，同时它能够缓存小写。
我认为 qi 肯定会对我添加到符号解析器。但它看起来不像。
所以我想出了我自己的，也是微不足道的实现，并使用静态 map 临时缓存的小写字母(请参阅附加源中的 impl3)。
测试结果:
Sooo，我想问题是为什么？
我是否以某种方式滥用了 qi::symbols？它实际上进行了二进制搜索但是性能在其他地方丢失了吗？
斯蒂芬¹
(我在 Windows MSVC14 64 位上，boost 1.66)
(¹ 这个问题是从 Spirit General 邮件列表中转述的，它发布于 20180112T14:15CET；online archives 似乎很遗憾地坏掉了)
最佳答案
在 12-01-18 14:15，Stephan Menzel 写道:
So I came up with two different implementations. Please find the source attached.
我看过了。首先进行一些粗略的观察:
您是在比较苹果和梨，因为 Beast 使用零拷贝字符串 View ，而 Qi 没有。
此外，样本选择调用 UB 因为 uniform_int_distribution(0,10)超出样本数组的范围(应为 (0, 9) )。
最后， map 方法没有 .txt 扩展名的映射。
有了这些，我将测试程序简化/结构化为以下内容:
在我的系统上打印以下内容:
Lambda runs took 2319 nanoseconds
Qi runs took 2841 nanoseconds
Map runs took 193 nanoseconds
现在，最大的罪魁祸首是(显然？)您每次都在通过循环构建语法(编译规则)。当然，没有必要。删除产量:
Lambda runs took 2676 nanoseconds
Qi runs took 98 nanoseconds
Map runs took 189 nanoseconds
这已经更快了，即使您在没有实际需要时仍在复制字符串。使用上面链接的答案的灵感，我可能会这样写:
#include <boost/spirit/include/qi.hpp>
namespace qi_impl {
namespace qi = boost::spirit::qi;
struct mimetype_symbols_type : qi::symbols<char, char const*> {
mimetype_symbols_type() {
auto rev = [](string_view s) -> std::string { return { s.rbegin(), s.rend() }; };
this->add
(rev(".htm"), "text/html")
(rev(".html"), "text/html")
(rev(".php"), "text/html")
(rev(".css"), "text/css")
(rev(".txt"), "text/plain")
(rev(".js"), "application/javascript")
(rev(".json"), "application/json")
(rev(".xml"), "application/xml")
(rev(".swf"), "application/x-shockwave-flash")
(rev(".flv"), "video/x-flv")
(rev(".png"), "image/png")
(rev(".jpe"), "image/jpeg")
(rev(".jpeg"), "image/jpeg")
(rev(".jpg"), "image/jpeg")
(rev(".gif"), "image/gif")
(rev(".bmp"), "image/bmp")
(rev(".ico"), "image/vnd.microsoft.icon")
(rev(".tiff"), "image/tiff")
(rev(".tif"), "image/tiff")
(rev(".svg"), "image/svg+xml")
(rev(".svgz"), "image/svg+xml")
;
}
} static const mime_symbols;
char const* using_spirit(const string_view &n_path) {
char const* result = "application/text";
qi::parse(n_path.crbegin(), n_path.crend(), qi::no_case[mime_symbols], result);
return result;
}
}
不再需要首先寻找“最后一个点”，也不需要“检查匹配项是否在末尾”，您可以直接从符号中获取值。您可以自由分配给 string_view或 std::string随心所欲。
自始至终使用 string_views(支持/显示 std::string_view 和 boost::string_view)。
Note also this shows a custom comparator being used on the
map<>approach, just to prove that indeed there's a benefit from knowing that the map keys are all lower-case. (It's not, in fact, because it "cached the lowercase" since it's only used once!)
#include <boost/chrono.hpp>
#include <string>
#ifdef BOOST_STRING_VIEW
#include <boost/utility/string_view.hpp>
using string_view = boost::string_view;
#else
#include <string_view>
using string_view = std::string_view;
#endif
static auto constexpr npos = string_view::npos;
#include <boost/spirit/include/qi.hpp>
namespace qi_impl {
namespace qi = boost::spirit::qi;
struct mimetype_symbols_type : qi::symbols<char, char const*> {
mimetype_symbols_type() {
auto rev = [](string_view s) -> std::string { return { s.rbegin(), s.rend() }; };
this->add
(rev(".htm"), "text/html")
(rev(".html"), "text/html")
(rev(".php"), "text/html")
(rev(".css"), "text/css")
(rev(".txt"), "text/plain")
(rev(".js"), "application/javascript")
(rev(".json"), "application/json")
(rev(".xml"), "application/xml")
(rev(".swf"), "application/x-shockwave-flash")
(rev(".flv"), "video/x-flv")
(rev(".png"), "image/png")
(rev(".jpe"), "image/jpeg")
(rev(".jpeg"), "image/jpeg")
(rev(".jpg"), "image/jpeg")
(rev(".gif"), "image/gif")
(rev(".bmp"), "image/bmp")
(rev(".ico"), "image/vnd.microsoft.icon")
(rev(".tiff"), "image/tiff")
(rev(".tif"), "image/tiff")
(rev(".svg"), "image/svg+xml")
(rev(".svgz"), "image/svg+xml")
;
}
} static const mime_symbols;
char const* using_spirit(const string_view &n_path) {
char const* result = "application/text";
qi::parse(n_path.crbegin(), n_path.crend(), qi::no_case[mime_symbols], result);
return result;
}
}
#include <boost/algorithm/string.hpp>
namespace impl {
string_view using_iequals(const string_view &n_path) {
using boost::algorithm::iequals;
auto const ext = [&n_path] {
auto pos = n_path.rfind(".");
return pos != npos? n_path.substr(pos) : string_view {};
}();
if (iequals(ext, ".htm")) return "text/html";
if (iequals(ext, ".html")) return "text/html";
if (iequals(ext, ".php")) return "text/html";
if (iequals(ext, ".css")) return "text/css";
if (iequals(ext, ".txt")) return "text/plain";
if (iequals(ext, ".js")) return "application/javascript";
if (iequals(ext, ".json")) return "application/json";
if (iequals(ext, ".xml")) return "application/xml";
if (iequals(ext, ".swf")) return "application/x-shockwave-flash";
if (iequals(ext, ".flv")) return "video/x-flv";
if (iequals(ext, ".png")) return "image/png";
if (iequals(ext, ".jpe")) return "image/jpeg";
if (iequals(ext, ".jpeg")) return "image/jpeg";
if (iequals(ext, ".jpg")) return "image/jpeg";
if (iequals(ext, ".gif")) return "image/gif";
if (iequals(ext, ".bmp")) return "image/bmp";
if (iequals(ext, ".ico")) return "image/vnd.microsoft.icon";
if (iequals(ext, ".tiff")) return "image/tiff";
if (iequals(ext, ".tif")) return "image/tiff";
if (iequals(ext, ".svg")) return "image/svg+xml";
if (iequals(ext, ".svgz")) return "image/svg+xml";
return "application/text";
}
}
#include <boost/algorithm/string.hpp>
#include <map>
namespace impl {
struct CiCmp {
template <typename R1, typename R2>
bool operator()(R1 const& a, R2 const& b) const {
return boost::algorithm::ilexicographical_compare(a, b);
}
};
static const std::map<string_view, string_view, CiCmp> s_mime_exts_map {
{ ".txt", "text/plain" },
{ ".htm", "text/html" },
{ ".html", "text/html" },
{ ".php", "text/html" },
{ ".css", "text/css" },
{ ".js", "application/javascript" },
{ ".json", "application/json" },
{ ".xml", "application/xml" },
{ ".swf", "application/x-shockwave-flash" },
{ ".flv", "video/x-flv" },
{ ".png", "image/png" },
{ ".jpe", "image/jpeg" },
{ ".jpeg", "image/jpeg" },
{ ".jpg", "image/jpeg" },
{ ".gif", "image/gif" },
{ ".bmp", "image/bmp" },
{ ".ico", "image/vnd.microsoft.icon" },
{ ".tif", "image/tiff" },
{ ".tiff", "image/tiff" },
{ ".svg", "image/svg+xml"},
{ ".svgz", "image/svg+xml"},
};
string_view using_map(const string_view& n_path) {
auto const ext = [](string_view n_path) {
auto pos = n_path.rfind(".");
return pos != npos? n_path.substr(pos) : string_view {};
};
auto i = s_mime_exts_map.find(ext(n_path));
if (i != s_mime_exts_map.cend()) {
return i->second;
} else {
return "application/text";
}
}
}
#include <random>
namespace samples {
static string_view const s_samples[] = {
"test.txt",
"test.html",
"longer/test.tiff",
"www.webSite.de/ico.ico",
"www.websIte.de/longEr/path/ico.bmp",
"www.TEST.com/longer/path/ico.svg",
"googlecom/shoRT/path/index.HTM",
"googlecom/bild.jpg",
"WWW.FLASH.COM/app.swf",
"WWW.FLASH.COM/BILD.GIF"
};
std::mt19937 s_random_generator(std::random_device{}());
std::uniform_int_distribution<> s_dis(0, boost::size(s_samples) - 1);
string_view random_sample() {
return s_samples[s_dis(s_random_generator)];
}
}
#include <boost/functional/hash.hpp>
#include <iostream>
template <typename F>
int generic_test(F f) {
auto sample = samples::random_sample();
string_view result = f(sample);
//std::cout << "DEBUG " << sample << " -> " << result << "\n";
return boost::hash_range(result.begin(), result.end());
}
#include <boost/serialization/array_wrapper.hpp> // missing include in boost version on coliru
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics.hpp>
template <typename F>
auto benchmark(F f) {
using C = boost::chrono::high_resolution_clock;
using duration = C::duration;
const unsigned int loops = 100000;
namespace ba = boost::accumulators;
ba::accumulator_set<duration, ba::features<ba::tag::mean>> times;
for (unsigned int i = 0; i < loops; i++) {
auto start = C::now();
generic_test(f);
times(C::now() - start);
}
return ba::mean(times);
}
int main() {
std::cout << std::unitbuf;
std::cout << "Lambda runs took " << benchmark(impl::using_iequals) << std::endl;
std::cout << "Qi runs took " << benchmark(qi_impl::using_spirit) << std::endl;
std::cout << "Map runs took " << benchmark(impl::using_map) << std::endl;
}
打印
Lambda runs took 2470 nanoseconds
Qi runs took 119 nanoseconds
Map runs took 2239 nanoseconds // see Note above
关于c++ - Qi Symbols 性能慢？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48235133/
27
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假设我们要解析一个内积表达式并得到结果。 "SUM({1, 2, 3} .* {4, 5, 6})" qi::_1 和 qi::_2 非常方便地在解析器中引用第 i 个属性。 void Test(st
无法弄清楚为什么这条规则 unary_msg 不起作用，它说属性类型是 qi::unused_type 但这对我来说毫无意义。为什么 boost 会这样折磨我？ template struct g3:
从测试中我可以得到 qi::uint_parser()与 qi::uint_ 相同.他们从 0 解析整数至 UINT_MAX . 我不明白的是qi::uint_parser需要 std::numeri
bool EqnExprEvaluator::SetEqn(const std::string& eqnStr) { typedef std::string::const_iterator
我一直在使用 Boost 库中的 Spirit Qi 用 C++ 编写语法。作为该语言的新手，很难习惯该库的语法和怪癖，但现在我有点了解它的工作原理。 我在使用 qi::lexeme 时遇到错误。我的
我需要跟踪一些项目在我使用提升灵气解析的文本中的位置。我找到了 this example并适应这样: #include #include #include #include #include
我想做的是在运行时从 ABNF 语法文件创建一个解析器。我已经在 qi::grammar 中实现了所有 ABNF 规则，如下所示: typedef /*qi::rule or struct conta
我在boost_1.59中使用spirit来解析类c语言(名为stone，最初由java编写)。但是我在使用 boost::spirit::qi 解析 c 风格的字符串时遇到了麻烦。整个代码位于 co
我正在用 Boost.Spirit 做一个 IRC 消息解析器，但是当我尝试解析一个输入时我遇到了一个(很长的)错误。我遵循了“Roman Numerals”示例。此外，我将 g++4.7 与 -st
如何解析可能包含 double 或 int 的字符串，具体取决于是否设置了点。例如。 6.0是double类型，6是int类型。规则是 rule,skipper> r = qi::double_|qi
在 boost::spirit::traits::transform_attribute 中指示解析失败的正确方法是什么？我可以抛出任何旧的异常，还是它要我做的特定事情？ namespace boos
我正在尝试使用 qi 创建通用解析器元素，因为不幸的是(必须支持 MSVC)无法使用 X3。这个想法是有一个模板化的结构: template struct parse_type; 我可以这样使用: t
我正在尝试创建一个返回 function 的规则通过柯里化(Currying) Phoenix 表达式构造。例如， start = int_[_val = xxx]; rule start; 应该做什
我正在解析一个文本文件，可能有几 GB 的大小，由以下几行组成: 11 0.1 14 0.78 532 -3.5 基本上，每行一个整数和一个 float 。整数应该是有序的并且是非负的。我想验证数据是
我想提出一个让我陷入困境的主题，并提出了一个关于齐::符号。 这一切都始于我查看新的野兽图书馆并阅读 atutorial example 它以一个从 http 路径猜测 mime 类型的函数开始扩展。
我有一段 boost::spirit::qi 代码可以匹配 "M7.x.y.z" 或 "M7.x.y.z "，但我想要一个在前一个输入上失败的解析器。 我想我需要在其中插入 qi::lexeme[]
我正在尝试为一种语言的多个子集定义一些 Boost::spirit::qi 解析器，代码重复最少。为此，我创建了一些基本的规则构建函数。原来的解析器工作正常，但一旦我开始使用组合函数，我的解析器似乎就
假设我有一个简单的类型foo: struct foo { void bar(int) { // do something } }; 我想使用 Boost.Qi 来解析字符串中的整数字段，并使用结果值调
(免责声明，我正在学习提升精神) 我正在尝试解析这样的表达式:F( 1 ) 并希望将 1 作为字符串(“1”而不是数字(与 qi::int_ 一起使用))。 我试过这样的事情(这是错误的，但也许我的方
假设我有两个用逗号分隔的 double 来解析返回它们的总和。在 Haskell 中我可能会这样做: import Data.Attoparsec.Text import Data.Text (pac
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