I'm trying to implement a HTTP header parser using Boost Spirit, however I've become stuck on a basic subtask: extracting the HTTP version number from the first line.
Simplified code:
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/adapted.hpp>
#include <boost/fusion/sequence.hpp>
#include <iostream>
#include <string>
namespace parser
{
namespace ast
{
struct version_number
{
int major = 0;
int minor = 0;
};
}
using boost::fusion::operator<<;
}
BOOST_FUSION_ADAPT_STRUCT(
parser::ast::version_number,
(int, major)
(int, minor)
)
namespace parser
{
using namespace boost::spirit::x3;
class version_number_id;
rule<version_number_id, ast::version_number> version_number = "version_number";
auto const version_number_def = eps
>> int_
>> "."
>> int_
;
BOOST_SPIRIT_DEFINE(rtsp_request_line)
}
int main()
{
using namespace std;
string input = "4.332";
parser::ast::version_number vn;
auto res = boost::spirit::x3::parse(begin(input), end(input), parser::version_number, vn);
if (res)
{
cout << "Success" << endl;
}
else
{
cout << "Failure" << endl;
}
}
However even with this simple example I've run into compilation errors using Boost v1.64 and MSVC++ 14.1. Compiler output is as follows:
1>------ Build started: Project: spirit_test, Configuration: Debug Win32 ------
1>main2.cpp
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\nonterminal\rule.hpp(36): error C2338: BOOST_SPIRIT_DEFINE undefined for this rule.
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\nonterminal\rule.hpp(116): note: see reference to function template instantiation 'boost::spirit::x3::detail::default_parse_rule_result boost::spirit::x3::parse_rule<parser::version_number_id,parser::ast::version_number,Iterator,Context,Attribute_>(boost::spirit::x3::rule<parser::version_number_id,parser::ast::version_number,false>,Iterator &,const Iterator &,const Context &,ActualAttribute &)' being compiled
1> with
1> [
1> Iterator=std::_String_iterator<std::_String_val<std::_Simple_types<char>>>,
1> Context=boost::spirit::x3::unused_type,
1> Attribute_=parser::ast::version_number,
1> ActualAttribute=parser::ast::version_number
1> ]
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\core\parse.hpp(35): note: see reference to function template instantiation 'bool boost::spirit::x3::rule<parser::version_number_id,parser::ast::version_number,false>::parse<Iterator,boost::spirit::x3::unused_type,Attribute>(Iterator &,const Iterator &,const Context &,boost::spirit::x3::unused_type,Attribute_ &) const' being compiled
1> with
1> [
1> Iterator=std::_String_iterator<std::_String_val<std::_Simple_types<char>>>,
1> Attribute=parser::ast::version_number,
1> Context=boost::spirit::x3::unused_type,
1> Attribute_=parser::ast::version_number
1> ]
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\core\parse.hpp(35): note: see reference to function template instantiation 'bool boost::spirit::x3::rule<parser::version_number_id,parser::ast::version_number,false>::parse<Iterator,boost::spirit::x3::unused_type,Attribute>(Iterator &,const Iterator &,const Context &,boost::spirit::x3::unused_type,Attribute_ &) const' being compiled
1> with
1> [
1> Iterator=std::_String_iterator<std::_String_val<std::_Simple_types<char>>>,
1> Attribute=parser::ast::version_number,
1> Context=boost::spirit::x3::unused_type,
1> Attribute_=parser::ast::version_number
1> ]
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\core\parse.hpp(60): note: see reference to function template instantiation 'bool boost::spirit::x3::parse_main<Iterator,Parser,Attribute>(Iterator &,Iterator,const Parser &,Attribute &)' being compiled
1> with
1> [
1> Iterator=std::_String_iterator<std::_String_val<std::_Simple_types<char>>>,
1> Parser=boost::spirit::x3::rule<parser::version_number_id,parser::ast::version_number,false>,
1> Attribute=parser::ast::version_number
1> ]
1>d:\documents\visual studio 2017\projects\spirit_test\spirit_test\main2.cpp(49): note: see reference to function template instantiation 'bool boost::spirit::x3::parse<std::_String_iterator<std::_String_val<std::_Simple_types<char>>>,boost::spirit::x3::rule<parser::version_number_id,parser::ast::version_number,false>,parser::ast::version_number>(const Iterator &,Iterator,const Parser &,Attribute &)' being compiled
1> with
1> [
1> Iterator=std::_String_iterator<std::_String_val<std::_Simple_types<char>>>,
1> Parser=boost::spirit::x3::rule<parser::version_number_id,parser::ast::version_number,false>,
1> Attribute=parser::ast::version_number
1> ]
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\nonterminal\rule.hpp(37): error C2039: 'parse': is not a member of 'boost::spirit::x3::unused_type'
1>c:\devlib\boost_1_64_0\include\boost\spirit\home\x3\support\traits\attribute_category.hpp(22): note: see declaration of 'boost::spirit::x3::unused_type'
1>Done building project "spirit_test.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped =========
I notice that in the debug messages, the Context=boost::spirit::x3::unused_type line appearing, and I known that unused_type is a tag class used to indicate that the rule does not populate an attribute. I don't understand where that tag is coming from in this example, however.
If I modify the code by using an inline rule with no rule<> definition, and pass a std::pair<int, int> in as the attribute instead, the code compiles and runs fine.
What's going on here, and where did I go wrong with this simple example?
