首先
我猜您的期望点太多>
,可能/应该是>>
序列运算符。
我会说,让你的语法更明确,例如说
bool_ | attr(false)
确保如果bool_
失败,将有一个结果属性值false
暴露。这样,暴露的属性是bool
,而不是boost::optional<bool>
,它与目标结构( )更兼容price
。
演示:
template <typename It, typename Skipper = qi::space_type>
struct parser : qi::grammar<It, price(), Skipper>
{
parser() : parser::base_type(start)
{
using namespace qi;
in_stock = bool_ | attr(false);
start = int_ > int_ > in_stock > -('"' >> char_ % ',' > '"');
}
private:
qi::rule<It, price(), Skipper> start;
qi::rule<It, bool()> in_stock;
};
第二
然后,
('"' > char_ % ',' > '"')
只会匹配字符串"a"
,"b,c,d"
等等。如果你想"Chili"
解析,你应该把它改成这样的:
place = '"' >> *~char_('"') > '"';
start = int_ > int_ > in_stock > (place | attr(""));
'"'
这意味着解析由(~char_("abc)
表示:除 [abc] 之外的任何字符)分隔的任何字符串。
样品溶液
这是一个完整的演示:
- 结构体的融合适配
- 以上调整语法
- 使用 BOOST_SPIRIT_DEBUG 调试
- 捕获
qi::expectation_failure
以在解析失败时打印诊断信息
- 使用 Spirit Karma 以人类可读的形式打印解析结果
下面列出的测试程序的输出:
代码
#define BOOST_SPIRIT_DEBUG
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp>
namespace qi = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace phx = boost::phoenix;
struct price
{
int chicken;
int cow;
bool in_stock;
std::string place;
};
BOOST_FUSION_ADAPT_STRUCT(price,
(int, chicken)
(int, cow)
(bool, in_stock)
(std::string, place))
template <typename It, typename Skipper = qi::space_type>
struct parser : qi::grammar<It, price(), Skipper>
{
parser() : parser::base_type(start)
{
using namespace qi;
in_stock = bool_ | attr(false);
#if 0
start = int_ > int_ > in_stock > -('"' >> char_ % ',' > '"');
#else
place = '"' >> *~char_('"') > '"';
start = int_ > int_ > in_stock > (place | attr(""));
#endif
BOOST_SPIRIT_DEBUG_NODE(start);
BOOST_SPIRIT_DEBUG_NODE(place);
BOOST_SPIRIT_DEBUG_NODE(in_stock);
}
private:
qi::rule<It, price(), Skipper> start;
//
qi::rule<It, bool()> in_stock;
qi::rule<It, std::string()> place; // no skipper
};
bool doParse(const std::string& input)
{
typedef std::string::const_iterator It;
auto f(begin(input)), l(end(input));
parser<It, qi::space_type> p;
price data;
try
{
bool ok = qi::phrase_parse(f,l,p,qi::space,data);
if (ok)
{
std::cout << "parse success: '" << input << "'\n";
std::cout << "data: " << karma::format_delimited(karma::eps <<
"chicken:" << karma::int_ <<
"cow:" << karma::int_ <<
"in_stock:" << karma::bool_ <<
"place:" << karma::auto_,
" ", data) << "\n";
}
else std::cerr << "parse failed: '" << std::string(f,l) << "'\n";
if (f!=l) std::cerr << "trailing unparsed: '" << std::string(f,l) << "'\n";
return ok;
} catch(const qi::expectation_failure<It>& e)
{
std::string frag(e.first, e.last);
std::cerr << e.what() << "'" << frag << "'\n";
}
return false;
}
int main()
{
doParse("1 2 true \"a,b,c,d,e,f\"");
doParse("3 4 \"a,b,c,d,e,f\"");
doParse("5 6");
doParse("7 8 false");
}
输出
<start>
<try>1 2 true "a,b,c,d,e,</try>
<in_stock>
<try>true "a,b,c,d,e,f"</try>
<success> "a,b,c,d,e,f"</success>
<attributes>[1]</attributes>
</in_stock>
<place>
<try>"a,b,c,d,e,f"</try>
<success></success>
<attributes>[[a, ,, b, ,, c, ,, d, ,, e, ,, f]]</attributes>
</place>
<success></success>
<attributes>[[1, 2, 1, [a, ,, b, ,, c, ,, d, ,, e, ,, f]]]</attributes>
</start>
parse success: '1 2 true "a,b,c,d,e,f"'
data: chicken: 1 cow: 2 in_stock: true place: a,b,c,d,e,f
<start>
<try>3 4 "a,b,c,d,e,f"</try>
<in_stock>
<try>"a,b,c,d,e,f"</try>
<success>"a,b,c,d,e,f"</success>
<attributes>[0]</attributes>
</in_stock>
<place>
<try>"a,b,c,d,e,f"</try>
<success></success>
<attributes>[[a, ,, b, ,, c, ,, d, ,, e, ,, f]]</attributes>
</place>
<success></success>
<attributes>[[3, 4, 0, [a, ,, b, ,, c, ,, d, ,, e, ,, f]]]</attributes>
</start>
parse success: '3 4 "a,b,c,d,e,f"'
data: chicken: 3 cow: 4 in_stock: false place: a,b,c,d,e,f
<start>
<try>5 6</try>
<in_stock>
<try></try>
<success></success>
<attributes>[0]</attributes>
</in_stock>
<place>
<try></try>
<fail/>
</place>
<success></success>
<attributes>[[5, 6, 0, []]]</attributes>
</start>
parse success: '5 6'
data: chicken: 5 cow: 6 in_stock: false place:
<start>
<try>7 8 false</try>
<in_stock>
<try>false</try>
<success></success>
<attributes>[0]</attributes>
</in_stock>
<place>
<try></try>
<fail/>
</place>
<success></success>
<attributes>[[7, 8, 0, []]]</attributes>
</start>
parse success: '7 8 false'
data: chicken: 7 cow: 8 in_stock: false place: