我正在尝试弄清楚如何解决以下问题。
我有以下格式的结构：
struct Data
{
time_t timestamp;
string id;
boost::optional<int> data1;
boost::optional<string> data2;
// etc...
};
这应该被解析为以下格式的单行字符串：
human_readable_timestamp;id;key1=value1 key2=value2.....
当然，键的顺序不必与结构中元素的顺序相匹配。
Boost::Spirit 是否适合这种类型的数据？我该如何处理？我已经浏览了这些示例，但我无法从示例中获得符合我要求的代码。
【问题讨论】：
标签： c++ boost boost-spirit boost-spirit-qi
您可以使用排列解析器。我在这里做了一个非常相似的例子：
如果您有重复键，那么使用Kleene* 可能更有意义，也许
如果您不想使用语义操作 (Boost Spirit: "Semantic actions are evil"?)，您可以稍微调整结构，以便在使用 data 元素的排列时匹配自动合成的属性类型：
struct Data
{
boost::posix_time::ptime timestamp;
std::string id;
struct Fields {
boost::optional<int> data1;
boost::optional<std::string> data2;
} fields;
};
现在解析器可以是：
timestamp = stream;
text = lexeme [ '"' >> *~char_('"') >> '"' ];
data1 = "key1" >> lit('=') >> int_;
data2 = "key2" >> lit('=') >> text;
id = lexeme [ *~char_(';') ];
start = timestamp >> ';' >> id >> ';' >> (data1 ^ data2);
对于评论，使其“有弹性”。我最终放弃了排列解析器，并采用了第一种编号方法（Kleene star with semantic actions 方法）。
id = lexeme [ *~char_(';') ];
auto data1 = bind(&Data::Fields::data1, _val);
auto data2 = bind(&Data::Fields::data2, _val);
other = lexeme [ +(graph-'=') ] >> '=' >> (real_|int_|text);
fields = *(
("key1" >> lit('=') >> int_) [ data1 = _1 ]
| ("key2" >> lit('=') >> text) [ data2 = _1 ]
| other
);
start = timestamp >> ';' >> id >> -(';' >> fields);
这会改变以下几个方面：
为了能够跳过“其他”字段，我需要为“其他”字段提出合理的语法：
other = lexeme [ +(graph-'=') ] >> '=' >> (real_|int_|text);
（允许键由除= 之外的任何非空格组成，后跟=，后跟数字（渴望）或文本）。
我扩展了文本的概念以支持流行的引用/转义方案：
text = lexeme [
'"' >> *('\\' >> char_ | ~char_('"')) >> '"'
| "'" >> *('\\' >> char_ | ~char_("'")) >> "'"
| *graph
];
它允许重复相同的键（在这种情况下，它保留上次看到的有效值）。
如果您想禁止无效值，请将>> int_ 或>> text 替换为> int_ 或> text（expectation parser）。
我用一些具有挑战性的案例扩展了测试用例：
2015-Jan-26 00:00:00;id
2015-Jan-26 14:59:24;id;key2="value"
2015-Jan-26 14:59:24;id;key2="value" key1=42
2015-Jan-26 14:59:24;id;key2="value" key1=42 something=awful __=4.74e-10 blarg;{blo;bloop='whatever \'ignor\'ed' key2="new} \"value\""
2015-Jan-26 14:59:24.123;id;key1=42 key2="value"
现在打印出来了
----------------------------------------
Parsing '2015-Jan-26 00:00:00;id'
Parsing success
2015-Jan-26 00:00:00 id
data1: --
data2: --
----------------------------------------
Parsing '2015-Jan-26 14:59:24;id;key2="value"'
Parsing success
2015-Jan-26 14:59:24 id
data1: --
data2: value
----------------------------------------
Parsing '2015-Jan-26 14:59:24;id;key2="value" key1=42'
Parsing success
2015-Jan-26 14:59:24 id
data1: 42
data2: value
----------------------------------------
Parsing '2015-Jan-26 14:59:24;id;key2="value" key1=42 something=awful __=4.74e-10 blarg;{blo;bloop='whatever \'ignor\'ed' key2="new} \"value\""'
Parsing success
2015-Jan-26 14:59:24 id
data1: 42
data2: new} "value"
----------------------------------------
Parsing '2015-Jan-26 14:59:24.123;id;key1=42 key2="value" '
Parsing success
2015-Jan-26 14:59:24.123000 id
data1: 42
data2: value
//#define BOOST_SPIRIT_DEBUG
#include <boost/optional/optional_io.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi = boost::spirit::qi;
namespace phx = boost::phoenix;
struct Data
{
boost::posix_time::ptime timestamp;
std::string id;
struct Fields {
boost::optional<int> data1;
boost::optional<std::string> data2;
} fields;
};
BOOST_FUSION_ADAPT_STRUCT(Data::Fields,
(boost::optional<int>, data1)
(boost::optional<std::string>, data2)
)
BOOST_FUSION_ADAPT_STRUCT(Data,
(boost::posix_time::ptime, timestamp)
(std::string, id)
(Data::Fields, fields)
)
template <typename It, typename Skipper = qi::space_type>
struct grammar : qi::grammar<It, Data(), Skipper> {
grammar() : grammar::base_type(start) {
using namespace qi;
timestamp = stream;
real_parser<double, strict_real_policies<double> > real_;
text = lexeme [
'"' >> *('\\' >> char_ | ~char_('"')) >> '"'
| "'" >> *('\\' >> char_ | ~char_("'")) >> "'"
| *graph
];
id = lexeme [ *~char_(';') ];
auto data1 = bind(&Data::Fields::data1, _val);
auto data2 = bind(&Data::Fields::data2, _val);
other = lexeme [ +(graph-'=') ] >> '=' >> (real_|int_|text);
fields = *(
("key1" >> lit('=') >> int_) [ data1 = _1 ]
| ("key2" >> lit('=') >> text) [ data2 = _1 ]
| other
);
start = timestamp >> ';' >> id >> -(';' >> fields);
BOOST_SPIRIT_DEBUG_NODES((timestamp)(id)(start)(text)(other)(fields))
}
private:
qi::rule<It, Skipper> other;
qi::rule<It, std::string(), Skipper> text, id;
qi::rule<It, boost::posix_time::ptime(), Skipper> timestamp;
qi::rule<It, Data::Fields(), Skipper> fields;
qi::rule<It, Data(), Skipper> start;
};
int main() {
using It = std::string::const_iterator;
for (std::string const input : {
"2015-Jan-26 00:00:00;id",
"2015-Jan-26 14:59:24;id;key2=\"value\"",
"2015-Jan-26 14:59:24;id;key2=\"value\" key1=42",
"2015-Jan-26 14:59:24;id;key2=\"value\" key1=42 something=awful __=4.74e-10 blarg;{blo;bloop='whatever \\'ignor\\'ed' key2=\"new} \\\"value\\\"\"",
"2015-Jan-26 14:59:24.123;id;key1=42 key2=\"value\" ",
})
{
std::cout << "----------------------------------------\nParsing '" << input << "'\n";
It f(input.begin()), l(input.end());
Data parsed;
bool ok = qi::phrase_parse(f,l,grammar<It>(),qi::space,parsed);
if (ok) {
std::cout << "Parsing success\n";
std::cout << parsed.timestamp << "\t" << parsed.id << "\n";
std::cout << "data1: " << parsed.fields.data1 << "\n";
std::cout << "data2: " << parsed.fields.data2 << "\n";
} else {
std::cout << "Parsing failed\n";
}
if (f!=l)
std::cout << "Remaining unparsed: '" << std::string(f,l) << "'\n";
}
}
【讨论】：
other = lexeme [ +(graph-'=') ] >> '=' >> (real_|int_|text); 而不仅仅是other = lexeme [ +(graph-'=') ] >> '=' >> text;