Boost spirit is a robust and efficiency parser and output generators libs for c++. Although it is
very fast, the
learning curve is steep.To better understand the library, I write down this post to record what I have learn from the exercises.
The implementation of spirit involve a lot of
TMP skills, unfortunately, c++11 still do not support
concepts, therefore the error messages of compile time are
almost unreadable, this is the biggest draw back for me.The other serious issue is
long compile time, spirit X3 may
reduce the compile times more than 50%, hope it come out quickly.The merits of spirit are obvious too,
very fast,
clear syntax(similar to
EBNF),
seamless integration with other c++ codes.
In this post I would try to transform the input from
0.5">If you are a premiere member of the lynda.com online training library,
or if you
5.19">are watching this tutorial on a DVD, you have access to the
exercise files used throughout the title.
To something like
1
00:00:00,500 --> 00:00:05,190
If you are a premiere member of the lynda.com online training library,
or if you
2
00:00:05,190 --> 00:00:11,800
are watching this tutorial on a DVD, you have access to
the exercise files used throughout the title.
step 1 : parse the string
template<typename Iterator>
bool parse_video_data(Iterator begin, Iterator end,
std::vector<std::pair<float, std::string>>
&data)
{
//if you don't want to insert the "\n\n" in to the string
bool const r = qi::parse(begin, end,
(qi::float_ >> qi::omit["\">"] >>
*~qi::char_('\n')) % *(qi::eol),
data);
//if you want to insert the "\n\n" to the string
//bool const r = qi::parse(begin, end,
// +(qi::float_ >> qi::omit["\">"] >>
// qi::raw[*~qi::char_('\n') >> *(qi::eol)]),
// data);
if(!r || begin != end){
return false;
}
return r;
}
This function will parse the time and the string into the vector "data".
ex : 0.5">if you are something
will parse to
float : 0.5
std::string : "if you are something"
step 2 : transform the times
There are many solutions to transform the times, like sscanf, stringstream, regular expression, hand made loop, spirit::karma and so on.For the sake of practice, I chose spirit::karma.
BOOST_FUSION_ADAPT_STRUCT(
spiritParser::transformData,
(size_t, index)
(std::vector<std::vector<int>>, nums)
)
template<typename OutputIterator>
struct videoGrammar : karma::grammar<OutputIterator, transformData()>
{
videoGrammar()
: videoGrammar::base_type(final_rule)
{
using karma::int_;
using karma::repeat;
using karma::right_align;
using karma::uint_;
first_rule = repeat(2)[right_align(2, '0')[int_ <<":"]]>>
right_align(2, '0')[int_] >>",">>
right_align(2, '0')[int_];
second_rule = first_rule >> " --> " >> first_rule >> "\n";
final_rule = uint_ >> "\n">> second_rule;
}
karma::rule<OutputIterator, transformData()> final_rule;
karma::rule<OutputIterator, std::vector<std::vector<int>>()> second_rule;
karma::rule<OutputIterator, std::vector<int>()> first_rule;
};
inline void generate_nums(std::vector<int> &nums, float data)
{
nums[0] = static_cast<int>(data / 3600);
nums[1] = static_cast<int>(std::floor(data) / 60) % 60;
nums[2] = static_cast<int>(std::floor(data)) % 60;
nums[3] = static_cast<int>((data - std::floor(data)) * 1000.0);
}
template<typename Iterator, typename Grammar>
bool generate_times(Iterator sink, Grammar &grammar, transformData &data,
size_t index, float fir, float sec)
{
data.index = index;
generate_nums(data.nums[0], fir);
generate_nums(data.nums[1], sec);
bool r = karma::generate(sink,
grammar,
data
);
return r;
}
Now we could transform the times from (0.5, 5.19) to (00:00:00,500 --> 00:00:05,190).
The codes can download from
github.
