I've written some rules to parse floats into two std::vector's of floats, which in turn are stored in a struct:
Data input:
#
# object name01
#
v -1.5701 33.8087 0.3592
v -24.0119 0.0050 21.7439
# a comment
vn 0.0000 0.5346 0.8451
vn 0.8331 0.5531 -0.0000
# another comment
Struct:
struct ObjParseData
{
ObjParseData() : verts(), norms() {}
std::vector<float> verts;
std::vector<float> norms;
};
And the relevant parsing code:
struct objGram : qi::grammar<std::string::const_iterator, ObjParseData(), iso8859::space_type>
{
objGram() : objGram::base_type(start)
{
vertex = 'v' >> qi::double_ >> qi::double_ >> qi::double_;
normal = "vn" >> qi::double_ >> qi::double_ >> qi::double_;
comment = '#' >> qi::skip(qi::blank)[ *(qi::print) ];
vertexList = *(vertex | comment);
normalList = *(normal | comment);
start = vertexList >> normalList;
}
qi::rule<std::string::const_iterator, ObjParseData(), iso8859::space_type> start;
qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> vertexList;
qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> normalList;
qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> vertex;
qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> normal;
qi::rule<std::string::const_iterator, iso8859::space_type> comment;
} objGrammar;
ObjParseData resultData;
std::string::const_iterator f = data.cbegin();
bool res = qi::phrase_parse( f, data.cend(), objGrammar, iso8859::space, resultData );
And this works. It parses all the floats preceded by 'v' into the verts vector of the struct and all floats preceded by "vn" into norms. Which is great, but I don't really know why this works.
Now if I understand this correctly, a rule defined like below puts all its results into a std::vector of floats.
qi::rule<std::string::const_iterator, std::vector<float>(), iso8859::space_type> vertex;
So, looking at the parsing code shown above and knowing that a rule like vertex parses into a std::vector of floats, apparently a rule like vertexList (the one shown above) concatenates the results from vertex into one std::vector of floats? So seeing this behaviour, you would think that you could just write those two rules (vertex and vertexList) as one, but unfortunately this doesn't work:
vertex = *('v' >> qi::double_ >> qi::double_ >> qi::double_) | comment;
normal = *("vn" >> qi::double_ >> qi::double_ >> qi::double_) | comment;
comment = '#' >> qi::skip(qi::blank)[ *(qi::print) ];
start = vertex >> normal;
The code does compile and qi::phrase_parse does return a succesfull parse, but the std::vector's in the struct aren't filled anymore.. What am I missing here?
You missplaced the grouping parentheses: expanding
vertexList = *(vertex | comment);
normalList = *(normal | comment);
by eliminating subrules leads to
vertex = *(('v' >> qi::double_ >> qi::double_ >> qi::double_) | comment);
normal = *(("vn" >> qi::double_ >> qi::double_ >> qi::double_) | comment);
or, as I'd prefer:
Full working sample (please make your code samples SSCCE next time? https://meta.stackexchange.com/questions/22754/sscce-how-to-provide-examples-for-programming-questions):
#include <iterator>
#include <fstream>
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace phx = boost::phoenix;
struct ObjParseData
{
ObjParseData() : verts(), norms() {}
std::vector<float> verts;
std::vector<float> norms;
};
BOOST_FUSION_ADAPT_STRUCT(ObjParseData, (std::vector<float>, verts)(std::vector<float>, norms))
template <typename It, typename Skipper = qi::space_type>
struct parser : qi::grammar<It, ObjParseData(), Skipper>
{
parser() : parser::base_type(start)
{
using namespace qi;
vertex = 'v' >> qi::double_ >> qi::double_ >> qi::double_;
normal = "vn" >> qi::double_ >> qi::double_ >> qi::double_;
comment = '#' >> qi::skip(qi::blank)[ *(qi::print) ];
#if 0
vertexList = *(vertex | comment);
normalList = *(normal | comment);
start = vertexList >> normalList;
#else
vertex = *(comment | ('v' >> qi::double_ >> qi::double_ >> qi::double_));
normal = *(comment | ("vn" >> qi::double_ >> qi::double_ >> qi::double_));
start = vertex >> normal;
#endif
BOOST_SPIRIT_DEBUG_NODE(start);
}
private:
qi::rule<std::string::const_iterator, ObjParseData(), qi::space_type> start;
qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> vertexList;
qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> normalList;
qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> vertex;
qi::rule<std::string::const_iterator, std::vector<float>(), qi::space_type> normal;
qi::rule<std::string::const_iterator, qi::space_type> comment;
};
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;
ObjParseData data;
try
{
bool ok = qi::phrase_parse(f,l,p,qi::space,data);
if (ok)
{
std::cout << "parse success\n";
std::cout << "data: " << karma::format_delimited(
"v: " << karma::auto_ << karma::eol <<
"n: " << karma::auto_ << karma::eol, ' ', data);
}
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()
{
std::ifstream ifs("input.txt", std::ios::binary);
ifs.unsetf(std::ios::skipws);
std::istreambuf_iterator<char> f(ifs), l;
bool ok = doParse({ f, l });
}
Output:
parse success
data: v: -1.57 33.809 0.359 -24.012 0.005 21.744
n: 0.0 0.535 0.845 0.833 0.553 0.0