问题
I've been trying to parse a string with Boost Spirit like following:
integer_count int1 int2 int3 ... intN
Where N is the integer_count. For example,
5 1 2 3 4 5
The code is following:
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <string>
namespace qi = boost::spirit::qi;
namespace spirit = boost::spirit;
namespace ascii = boost::spirit::ascii;
using boost::phoenix::ref;
template <typename Iterator>
struct x_grammar : public qi::grammar<Iterator, std::string(), ascii::space_type>
{
public:
x_grammar() : x_grammar::base_type(start_rule, "x_grammar")
{
using namespace qi;
int repeat_count = 0;
start_rule = int_[ref(repeat_count) = _1] > repeater > *char_;
std::cout << "repeat_count == " << repeat_count << std::endl;
repeater = repeat(repeat_count)[int_[std::cout << _1 << ".\n"]];
}
private:
qi::rule<Iterator, std::string(), ascii::space_type> start_rule;
qi::rule<Iterator, std::string(), ascii::space_type> repeater;
};
int main()
{
typedef std::string::const_iterator iter;
std::string storage("5 1 2 3 4 5 garbage");
iter it_begin(storage.begin());
iter it_end(storage.end());
std::string read_data;
using boost::spirit::ascii::space;
x_grammar<iter> g;
try {
bool r = qi::phrase_parse(it_begin, it_end, g, space, read_data);
if(r) {
std::cout << "Pass!\n";
} else {
std::cout << "Fail!\n";
}
} catch (const qi::expectation_failure<iter>& x) {
std::cout << "Fail!\n";
}
}
The output is:
repeat_count == 0
Pass!
Which means that
ref(repeat_count) = _1
Was never invoked. So is there a way to read an integer runtime into a local variable and use that value for further parsing?
回答1:
I think you meant
repeat(boost::phoenix::ref(repeat_count))
Also, automatic attribute propagation is disabled for a rule when there are semantic actions. You can use %=
to force attribute propagation
Here's a simple fixed version Live On Coliru
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <string>
namespace qi = boost::spirit::qi;
namespace spirit = boost::spirit;
namespace ascii = boost::spirit::ascii;
using boost::phoenix::ref;
template <typename Iterator>
struct x_grammar : public qi::grammar<Iterator, ascii::space_type>
{
public:
x_grammar() : x_grammar::base_type(start_rule, "x_grammar")
{
using namespace qi;
int repeat_count = 0;
start_rule = int_[ref(repeat_count) = _1] > repeater > *char_;
std::cout << "repeat_count == " << repeat_count << std::endl;
repeater = repeat(ref(repeat_count))[int_[std::cout << _1 << ".\n"]];
}
private:
qi::rule<Iterator, ascii::space_type> start_rule;
qi::rule<Iterator, ascii::space_type> repeater;
};
int main()
{
typedef std::string::const_iterator iter;
std::string storage("5 1 2 3 4 5 garbage");
iter it_begin(storage.begin());
iter it_end(storage.end());
using boost::spirit::ascii::space;
x_grammar<iter> g;
try {
bool r = qi::phrase_parse(it_begin, it_end, g, space);
if(r) {
std::cout << "Pass!\n";
} else {
std::cout << "Fail!\n";
}
} catch (const qi::expectation_failure<iter>& x) {
std::cout << "Fail!\n";
}
}
Prints
repeat_count == 0
1.
2.
3.
4.
5.
Pass!
Note How, obviously, repeat_count == 0
is always printed, since it's executed during grammar construction, not parsing.
来源:https://stackoverflow.com/questions/23757504/boost-spirit-semantic-action-not-invoked