问题
I have trouble with boost spirit to parse a file like that :
int [int, int, int] [ int, int]
...
Nothing really hard, the following grammar works for that:
template<typename Iterator>
struct parser_expression : qi::grammar<Iterator,ascii::space_type>
{
parser_expression() : parser_expression::base_type(start) {
using qi::double_;
using qi::int_;
using boost::spirit::qi::char_;
using qi::alpha;
using qi::alnum;
using qi::digit;
using qi::eps;
using qi::_val;
using boost::phoenix::bind;
start = int_ >> list1 >> list2 >> char_('=');
list1 = ('[' >> int_ >> *(char_(',') >> int_ ) >> char_(']')) | (char_('[') >> char_(']'));
list2 = ('[' >> int_ >> *(char_(',') >> int_ ) >> char_(']')) | -(char_('[') >> char_(']'));
}
qi::rule<Iterator,ascii::space_type> start;
qi::rule<Iterator,ascii::space_type> list1;
qi::rule<Iterator,ascii::space_type> list2;
};
My problem is that I need to save the result of parsing. For example, I need to save the list1 and list2 of int to a custom list template :
template <typename T>
class SimpleLinkList {
private:
ChainLink<T>* head;
...
}
where ChainLink is :
template<typename T>
class ChainLink {
private:
T object;
ChainLink* next;
...
}
I have a method pushback in SimpleLinkList just like vector but I don't understand how to parse int, save it to a ChainLink and add it to a SimpleLinkList.
I've already seen how to adapt a template structure to a fusion sequence at http://boost-spirit.com/home/2010/02/08/how-to-adapt-templates-as-a-fusion-sequence/.
I need a custom LinkList to be able to delete and add items while looping on it.
I need help to understand how I can arrange all of that to successfully parse my file.
Thx for your help.
回答1:
You're probably looking for the container attribute customization points:
- boost::spirit::traits::container_value
- boost::spirit::traits::push_back
- boost::spirit::traits::clear_value
For your type, it would look like:
namespace boost { namespace spirit { namespace traits {
template <typename T>
struct container_value<SimpleLinkList<T>, void> {
typedef T type;
};
template <typename T>
struct push_back_container<SimpleLinkList<T>, T, void> {
static bool call(SimpleLinkList<T>& c, T const& val) {
c.push_back(val);
return true;
}
};
}}}
A simple demonstration (using a dummy implementation of SimpleLinkList):
struct AbstractDataType
{
int number;
SimpleLinkList<int> list1, list2;
};
BOOST_FUSION_ADAPT_STRUCT(AbstractDataType, (int, number)(SimpleLinkList<int>, list1)(SimpleLinkList<int>, list2))
template<typename Iterator>
struct parser_expression : qi::grammar<Iterator, AbstractDataType(), qi::space_type>
{
parser_expression() : parser_expression::base_type(start)
{
list = '[' >> -(qi::int_ % ',') >> ']';
start = qi::int_ >> list >> -list >> '=';
BOOST_SPIRIT_DEBUG_NODES((list)(start))
}
qi::rule<Iterator, AbstractDataType(), qi::space_type> start;
qi::rule<Iterator, SimpleLinkList<int>(), qi::space_type> list;
};
Note
- I replaced
qi::char_by (implicit)qi::litwhere possible, because you don't actually want to parse the punctuation characters into the attribute (right?) - I used the list parser operator
%instead of the verbose alternative - I used parser operator
-to make the element list optional (allow zero elements) - Similarly used
list >> -listto make the second list optional alltogether.
The following testcases:
void test(const std::string input)
{
static const parser_expression<std::string::const_iterator> p;
AbstractDataType parsed;
auto f(input.begin()), l(input.end());
bool ok = qi::phrase_parse(f, l, p, qi::space, parsed);
if (ok)
std::cout << "Result: " << parsed.number << " " << parsed.list1 << parsed.list2 << "\n";
else
std::cout << "Parse failed\n";
if (f!=l)
std::cout << "Unparsed: '" << std::string(f,l) << "'\n";
}
int main()
{
test("1 [2, 3, 4] [5, 6] =");
test("2 [] [6, 7] =");
test("3 [4, 5, 6] [ ] =");
test("4 [5, 6, 7] =");
}
Print the output:
Result: 1 [2 3 4 ][5 6 ]
Result: 2 [][6 7 ]
Result: 3 [4 5 6 ][]
Result: 4 [5 6 7 ][]
See it all integrated: http://ideone.com/odqhBz. Preventing linkrot:
// #define BOOST_SPIRIT_DEBUG
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi = boost::spirit::qi;
template <typename T> struct ChainLink;
template <typename T>
class SimpleLinkList {
public:
void push_back(T const& v) { /* todo */ _for_debug.push_back(v); }
std::list<int> _for_debug;
friend std::ostream& operator<<(std::ostream& os, SimpleLinkList const& list) {
os << "["; std::copy(list._for_debug.begin(), list._for_debug.end(), std::ostream_iterator<T>(os, " ")); return os << "]";
}
private:
ChainLink<T>* head;
};
namespace boost { namespace spirit { namespace traits {
template <typename T>
struct container_value<SimpleLinkList<T>, void> {
typedef T type;
};
template <typename T>
struct push_back_container<SimpleLinkList<T>, T, void> {
static bool call(SimpleLinkList<T>& c, T const& val) {
c.push_back(val);
return true;
}
};
}}}
struct AbstractDataType
{
int number;
SimpleLinkList<int> list1, list2;
};
BOOST_FUSION_ADAPT_STRUCT(AbstractDataType, (int, number)(SimpleLinkList<int>, list1)(SimpleLinkList<int>, list2))
template<typename Iterator>
struct parser_expression : qi::grammar<Iterator, AbstractDataType(), qi::space_type>
{
parser_expression() : parser_expression::base_type(start)
{
list = '[' >> -(qi::int_ % ',') >> ']';
start = qi::int_ >> list >> -list >> '=';
BOOST_SPIRIT_DEBUG_NODES((list)(start))
}
qi::rule<Iterator, AbstractDataType(), qi::space_type> start;
qi::rule<Iterator, SimpleLinkList<int>(), qi::space_type> list;
};
void test(const std::string input)
{
static const parser_expression<std::string::const_iterator> p;
AbstractDataType parsed;
auto f(input.begin()), l(input.end());
bool ok = qi::phrase_parse(f, l, p, qi::space, parsed);
if (ok)
std::cout << "Result: " << parsed.number << " " << parsed.list1 << parsed.list2 << "\n";
else
std::cout << "Parse failed\n";
if (f!=l)
std::cout << "Unparsed: '" << std::string(f,l) << "'\n";
}
int main()
{
test("1 [2, 3, 4] [5, 6] =");
test("2 [] [6, 7] =");
test("3 [4, 5, 6] [ ] =");
test("4 [5, 6, 7] =");
}
来源：https://stackoverflow.com/questions/17042851/boost-spirit-parse-integer-to-custom-list-template