boost::posix_time 格式标志的奇怪行为
[英]strange behaviour of format flag in boost::posix_time
问题描述
我有一个包含两个时间戳的字符串。 我正在尝试将两个时间戳都转换为 boost::posix_time::ptime。
字符串格式如下： "ASTRO20220923.1435+0000-20220923.1440+0000"我在boost::posix_time::time_input_facet中使用的第二个时间戳格式是".*+A%Y%m%d.%H%M" 。
我得到正确的 output 但我不明白我是如何得到它的。 在搜索格式标志时，我找不到任何标志为".*"或"+A" 。 有人可以帮助解释为什么会发生这种行为吗？
#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>
int main()
{
std::string timeStr = "ASTRO20220923.1435+0000-20220923.1440+0000";
std::stringstream ss;
boost::posix_time::ptime pTimeStart;
ss.imbue(std::locale(ss.getloc(), new boost::posix_time::time_input_facet("ASTRO%Y%m%d.%H%M.*")));
ss << timeStr;
ss >> pTimeStart;
std::cout << "START: " << boost::posix_time::to_simple_string(pTimeStart) << std::endl;
boost::posix_time::ptime pTimeEnd;
ss.imbue(std::locale(ss.getloc(), new boost::posix_time::time_input_facet(".*+A%Y%m%d.%H%M")));
ss << timeStr;
ss >> pTimeEnd;
std::cout << "END : " << boost::posix_time::to_simple_string(pTimeEnd) << std::endl;
return 0;
}
1 个解决方案
解决方案1
3 已采纳 2023-01-27 16:46:33
解释
Boost 输入方面将任何非字段输入字符视为通配符：它匹配任何输入字符。 这适用于控制代码甚至嵌入的 NUL 字符。 这些都没有记录在案，坦率地说似乎很可疑。 看看这个可笑的测试程序：
这表明所有选择的通配符都成功了，无论多么牵强：
DEBUG : '.....%Y%m%d.%H%M..', '....%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'AAAAA%Y%m%d.%H%MAA', 'AAAA%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'BBBBB%Y%m%d.%H%MBB', 'BBBB%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'CCCCC%Y%m%d.%H%MCC', 'CCCC%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'DDDDD%Y%m%d.%H%MDD', 'DDDD%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'EEEEE%Y%m%d.%H%MEE', 'EEEE%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'fffff%Y%m%d.%H%Mff', 'ffff%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'ggggg%Y%m%d.%H%Mgg', 'gggg%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'hhhhh%Y%m%d.%H%Mhh', 'hhhh%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'iiiii%Y%m%d.%H%Mii', 'iiii%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'jjjjj%Y%m%d.%H%Mjj', 'jjjj%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'kkkkk%Y%m%d.%H%Mkk', 'kkkk%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'lllll%Y%m%d.%H%Mll', 'llll%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'mmmmm%Y%m%d.%H%Mmm', 'mmmm%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : 'nnnnn%Y%m%d.%H%Mnn', 'nnnn%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '11111%Y%m%d.%H%M11', '1111%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '22222%Y%m%d.%H%M22', '2222%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '33333%Y%m%d.%H%M33', '3333%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '44444%Y%m%d.%H%M44', '4444%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '55555%Y%m%d.%H%M55', '5555%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '66666%Y%m%d.%H%M66', '6666%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '77777%Y%m%d.%H%M77', '7777%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '88888%Y%m%d.%H%M88', '8888%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '99999%Y%m%d.%H%M99', '9999%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '00000%Y%m%d.%H%M00', '0000%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '_____%Y%m%d.%H%M__', '____%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '-----%Y%m%d.%H%M--', '----%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '/////%Y%m%d.%H%M//', '////%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '?????%Y%m%d.%H%M??', '????%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '*****%Y%m%d.%H%M**', '****%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '\\\\\\\\\\%Y%m%d.%H%M\\\\', '\\\\\\\\%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '"""""%Y%m%d.%H%M""', '""""%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : "'''''%Y%m%d.%H%M''", "''''%Y%m%d.%H%M" START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '[[[[[%Y%m%d.%H%M[[', '[[[[%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : ']]]]]%Y%m%d.%H%M]]', ']]]]%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '(((((%Y%m%d.%H%M((', '((((%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : ')))))%Y%m%d.%H%M))', '))))%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '&&&&&%Y%m%d.%H%M&&', '&&&&%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '^^^^^%Y%m%d.%H%M^^', '^^^^%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '$$$$$%Y%m%d.%H%M$$', '$$$$%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '#####%Y%m%d.%H%M##', '####%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '@@@@@%Y%m%d.%H%M@@', '@@@@%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '!!!!!%Y%m%d.%H%M!!', '!!!!%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : ' %Y%m%d.%H%M ', ' %Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '
%Y%m%d.%H%M
', '
%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '
%Y%m%d.%H%M
', '
%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : ' %Y%m%d.%H%M ', ' %Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
DEBUG : '%Y%m%d.%H%M', '%Y%m%d.%H%M' START: 1400-Jan-01 00:00:00 END: 1400-Jan-01 00:00:00 IGNORED: ASTRO20220923.1435+0000-20220923.1440+0000 (true)
DEBUG : '%Y%m%d.%H%M', '%Y%m%d.%H%M' START: 2022-Sep-23 14:35:00 END: 2022-Sep-23 14:40:00 IGNORED: +0000 (true)
精神解析
要使用给定格式解析开始/结束时间段，我首先不会使用构面，因为没有一种格式显示为区域设置感知。 您使用ptime （不是local_date_time ）这一事实证实时区指示 (+0000) 并不重要。
所以，这是你可以写的：
// #define BOOST_SPIRIT_X3_DEBUG
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/fusion/adapted/std_tuple.hpp>
#include <boost/spirit/home/x3.hpp>
#include <iostream>
using boost::posix_time::ptime;
namespace Astro {
namespace Parser {
namespace x3 = boost::spirit::x3;
using Part = unsigned short;
using Parts = std::tuple<Part, Part, Part, Part, Part>;
static auto const dig4 = x3::uint_parser<Part, 10, 4, 4>{};
static auto const dig2 = x3::uint_parser<Part, 10, 2, 2>{};
static auto const timeformat
= x3::rule<struct partsformat_, Parts>{"timeformat"}
= dig4 >> dig2 >> dig2 >> '.' >> dig2 >> dig2 >> "+0000";
static auto const period //
= "ASTRO" >> Parser::timeformat >> "-" >> Parser::timeformat >> x3::eoi;
} // namespace Parser
ptime to_ptime(Parser::Parts const& p) {
auto [yyyy, mm, dd, HH, MM] = p;
return {{yyyy, mm, dd}, boost::posix_time::hours(HH) + boost::posix_time::minutes(MM)};
}
struct Period {
ptime start, end;
};
Period parsePeriod(std::string_view input) {
Parser::Parts s, e;
auto both = std::tie(s, e);
if (parse(begin(input), end(input), Parser::period, both))
return {to_ptime(s), to_ptime(e)};
throw std::runtime_error("parsePeriod");
}
}
int main() {
auto [s, e] = Astro::parsePeriod("ASTRO20220923.1435+0000-20220923.1440+0000");
std::cout << "start: " << s << "\n";
std::cout << "end: " << e << "\n";
}
印刷
start: 2022-Sep-23 14:35:00
end: 2022-Sep-23 14:40:00
如果你真的需要 stream 支持，你可以在上面构建它：
template <typename It>
bool parsePeriod(It& f, It l, Period& into, bool require_eoi = true) {
Parser::Parts s, e;
auto parts = std::tie(s, e);
bool ok = parse(f, l, Parser::period , parts);
if (ok) {
into = {to_ptime(s), to_ptime(e)};
if (require_eoi)
ok = ok && (f == l);
}
return ok;
}
Period parsePeriod(std::string_view input) {
Period result;
auto f = begin(input), l = end(input);
if (!parsePeriod(f, l, result, true))
throw std::runtime_error("parsePeriod");
return result;
}
std::istream& operator>>(std::istream& is, Period& period) {
auto saved = is.flags();
boost::spirit::istream_iterator f(is >> std::noskipws), l;
if (!parsePeriod(f, l, period , false))
is.setstate(std::ios::failbit);
is.flags(saved);
return is;
}
这允许您以相同的方式使用它：
std::istringstream iss("ASTRO20220923.1435+0000-20220923.1440+0000");
Astro::Period p;
if (iss >> p) {
std::cout << "start: " << p.start << "\n";
std::cout << "end: " << p.end << "\n";
} else {
std::cout << "Parse error\n";
}
印刷
start: 2022-Sep-23 14:35:00
end: 2022-Sep-23 14:40:00
基准！
为了说明输入方面的效率是多么低下，我做了一个基准测试。
它包括
- 问题代码（使用提升输入方面）
- 天真地使用了这个方面，但删除了问题中的一些问题
- 运用所有 Clever™ 技巧在提升输入方面进行优化
- 我的精灵X3版
这是时间安排（使用Nonius ）：（点击查看带有详细示例的交互式图表）
基准代码： Coliru
#include <iostream>
#include <boost/date_time/posix_time/posix_time.hpp>
namespace FacetQuestionCode {
// code from the question, already removing output and one unnecessary allocation (`timeStr` is now a
// string view)
//
// - still has unnecessary facet instantiation/destruction, locale creation/destruction, spurious double
// stream insertion and no error detection
auto parsePeriod(std::string_view timeStr) {
std::stringstream ss;
boost::posix_time::ptime pTimeStart;
ss.imbue(std::locale(ss.getloc(), new boost::posix_time::time_input_facet("ASTRO%Y%m%d.%H%M.*")));
ss << timeStr;
ss >> pTimeStart;
// std::cout << "START: " << boost::posix_time::to_simple_string(pTimeStart) << std::endl;
boost::posix_time::ptime pTimeEnd;
ss.imbue(std::locale(ss.getloc(), new boost::posix_time::time_input_facet(".*+A%Y%m%d.%H%M")));
ss << timeStr;
ss >> pTimeEnd;
// std::cout << "END : " << boost::posix_time::to_simple_string(pTimeEnd) << std::endl;
return std::pair(pTimeStart, pTimeEnd);
}
}
namespace FacetNaive {
// undocumented behaviour, error-prone because not-specifc
auto parsePeriod(std::string_view input) {
std::stringstream ss{std::string(input)};
auto* facet = new boost::posix_time::time_input_facet();
ss.exceptions(std::ios::failbit | std::ios::badbit);
ss.imbue(std::locale(ss.getloc(), facet));
boost::posix_time::ptime s, e;
facet->format("?????%Y%m%d.%H%M??"); ss >> s;
facet->format("????%Y%m%d.%H%M?????"); ss >> e;
return std::pair(s, e);
}
}
namespace FacetClever {
// undocumented behaviour, error-prone because not-specifc
// very dirty optimization tricks
auto parsePeriod(std::string_view input) {
thread_local std::stringstream ss;
thread_local boost::posix_time::time_input_facet* facet = [&] {
auto tmp = new boost::posix_time::time_input_facet();
ss.exceptions(std::ios::failbit | std::ios::badbit);
ss.imbue(std::locale(ss.getloc(), tmp));
return tmp;
}();
ss.clear();
ss.str(std::string(input));
boost::posix_time::ptime s, e;
facet->format("?????%Y%m%d.%H%M??"); ss >> s;
facet->format("????%Y%m%d.%H%M?????"); ss >> e;
return std::pair(s, e);
}
}
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/fusion/adapted/std_tuple.hpp>
#include <boost/spirit/home/x3.hpp>
namespace SpiritX3 {
namespace Parser {
namespace x3 = boost::spirit::x3;
using Part = unsigned short;
using Parts = std::tuple<Part, Part, Part, Part, Part>;
static auto const dig4 = x3::uint_parser<Part, 10, 4, 4>{};
static auto const dig2 = x3::uint_parser<Part, 10, 2, 2>{};
static auto const timeformat
= x3::rule<struct partsformat_, Parts>{"timeformat"}
= dig4 >> dig2 >> dig2 >> '.' >> dig2 >> dig2 >> "+0000";
static auto const period //
= "ASTRO" >> Parser::timeformat >> "-" >> Parser::timeformat >> x3::eoi;
} // namespace Parser
boost::posix_time::ptime to_ptime(Parser::Parts const& p) {
auto [yyyy, mm, dd, HH, MM] = p;
return {{yyyy, mm, dd}, boost::posix_time::hours(HH) + boost::posix_time::minutes(MM)};
}
struct Period {
boost::posix_time::ptime start, end;
};
Period parsePeriod(std::string_view input) {
Parser::Parts s, e;
auto both = std::tie(s, e);
if (parse(begin(input), end(input), Parser::period, both))
return {to_ptime(s), to_ptime(e)};
throw std::runtime_error("parsePeriod");
}
}
#define NONIUS_RUNNER
#include <nonius/benchmark.h++>
#include <nonius/main.h++>
constexpr auto input = "ASTRO20220923.1435+0000-20220923.1440+0000";
NONIUS_BENCHMARK("FacetQuestionCode", []{ FacetQuestionCode::parsePeriod(input); })
NONIUS_BENCHMARK("FacetNaive", []{ FacetNaive::parsePeriod(input); })
NONIUS_BENCHMARK("FacetClever", []{ FacetClever::parsePeriod(input); })
NONIUS_BENCHMARK("SpiritX3", []{ SpiritX3::parsePeriod(input); })
注意如何：
-
FacetNaive已经比FacetQuestionCode快 2 倍 - 使用分面的 Too Clever By Far(TM) 优化版本仍然比 Spirit 慢 20 倍
- 所有方面的版本都缺乏特异性并依赖于未记录的行为
- Spirit 版本实际上比原始代码快 11,000 倍，相对偏差也较小
这个选择似乎并不难。
boost :: posix_time :: time_facet和boost :: posix_time :: time_input_facet之间的'％f'行为不一致
[英]Inconsistent '%f' behaviour between boost::posix_time::time_facet and boost::posix_time::time_input_facet
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