boostini
Deal with duplicate section names in INI files
I need to load these values from INI file and print them in the application using C++ Boost Library. The sections have duplicate names. I have been restricted to using C++ Boost Library only.
numColors = 4
boardSize = 11
numSnails = 2
[initialization]
id = 0
row = 3
col = 4
orientation = 0
[initialization]
id = 1
row = 5
col = 0
orientation = 1
[color]
id = 0
nextColor = 1
deltaOrientation = +2
[color]
id = 1
nextColor = 2
deltaOrientation = +1
[color]
id = 2
nextColor = 3
deltaOrientation = -2
[color]
id = 3
nextColor = 0
deltaOrientation = -1
Solution
What It Isn't
In short, this is not INI format at all. It just very loosely resembles it. Which is nice.
What Is It Instead?
You don't specify a lot, so I'm going to make assumptions.
I'm going to, for simplicity, assume that
- initialization sections precede color sections
- keys in like sections have the same order always
- all keys shown are mandatory in like sections
- the deltas are signed integral values (positive sign being optional)
- all other values are non-negative integral numbers
- whitespace is not significant
- case is significant
- all numbers are in decimal form (regardless of leading zeros)
Non-essential deductions (could be used to add more validation):
- the number of of initializations = numSnails
- the board size dictates row and col are in [0, boardSize)
Data Structures
To represent the file, I'd make:
namespace Ast {
struct Initialization {
unsigned id, row, col, orientation;
};
struct Color {
unsigned id, nextColor;
int deltaOrientation;
};
struct File {
unsigned numColors, boardSize, numSnails;
std::vector<Initialization> initializations;
std::vector<Color> colors;
};
}
That's the simplest I can think of.
Parsing It
Is a nice job for Boost Spirit. If we adapt the data structures as Fusion Sequences:
BOOST_FUSION_ADAPT_STRUCT(Ast::Initialization, id, row, col, orientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::Color, id, nextColor, deltaOrientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::File, numColors, boardSize, numSnails,
initializations, colors)
We can basically let the parser "write itself":
template <typename It>
struct GameParser : qi::grammar<It, Ast::File()> {
GameParser() : GameParser::base_type(start) {
using namespace qi;
start = skip(blank)[file];
auto section = [](std::string name) {
return copy('[' >> lexeme[lit(name)] >> ']' >> (+eol | eoi));
};
auto required = [](std::string name) {
return copy(lexeme[eps > lit(name)] > '=' > auto_ >
(+eol | eoi));
};
file =
required("numColors") >
required("boardSize") >
required("numSnails") >
*initialization >
*color >
eoi; // must reach end of input
initialization = section("initialization") >
required("id") >
required("row") >
required("col") >
required("orientation");
color = section("color") >
required("id") >
required("nextColor") >
required("deltaOrientation");
BOOST_SPIRIT_DEBUG_NODES((file)(initialization)(color))
}
private:
using Skipper = qi::blank_type;
qi::rule<It, Ast::File()> start;
qi::rule<It, Ast::File(), Skipper> file;
qi::rule<It, Ast::Initialization(), Skipper> initialization;
qi::rule<It, Ast::Color(), Skipper> color;
};
Because of the many assumptions we've made we littered the place with expectation points (operator> sequences, instead of operator>>). This means we get "helpful" error messages on invalid input, like
Expected: nextColor
Expected: =
Expected: <eoi>
See also BONUS section below that improves this a lot
Testing/Live Demo
Testing it, we will read the file first and then parse it using that parser:
std::string read_file(std::string name) {
std::ifstream ifs(name);
return std::string(std::istreambuf_iterator<char>(ifs), {});
}
static Ast::File parse_game(std::string_view input) {
using SVI = std::string_view::const_iterator;
static const GameParser<SVI> parser{};
try {
Ast::File parsed;
if (qi::parse(input.begin(), input.end(), parser, parsed)) {
return parsed;
}
throw std::runtime_error("Unable to parse game");
} catch (qi::expectation_failure<SVI> const& ef) {
std::ostringstream oss;
oss << "Expected: " << ef.what_;
throw std::runtime_error(oss.str());
}
}
A lot could be improved, but for now it works and parses your input:
int main() {
std::string game_save = read_file("input.txt");
Ast::File data = parse_game(game_save);
}
The absense of output means success.
BONUS
Some improvements, instead of using auto_ to generate the right parser for the type, we can make that explicit:
namespace Ast {
using Id = unsigned;
using Size = uint8_t;
using Coord = Size;
using ColorNumber = Size;
using Orientation = Size;
using Delta = signed;
struct Initialization {
Id id;
Coord row;
Coord col;
Orientation orientation;
};
struct Color {
Id id;
ColorNumber nextColor;
Delta deltaOrientation;
};
struct File {
Size numColors{}, boardSize{}, numSnails{};
std::vector<Initialization> initializations;
std::vector<Color> colors;
};
} // namespace Ast
And then in the parser define the analogous:
qi::uint_parser<Ast::Id> _id;
qi::uint_parser<Ast::Size> _size;
qi::uint_parser<Ast::Coord> _coord;
qi::uint_parser<Ast::ColorNumber> _colorNumber;
qi::uint_parser<Ast::Orientation> _orientation;
qi::int_parser<Ast::Delta> _delta;
Which we then use e.g.:
initialization = section("initialization") >
required("id", _id) >
required("row", _coord) >
required("col", _coord) >
required("orientation", _orientation);
Now we can improve the error messages to be e.g.:
input.txt:2:13 Expected: <unsigned-integer>
note: boardSize = (11)
note: ^--- here
Or
input.txt:16:19 Expected: <alternative><eol><eoi>
note: nextColor = 1 deltaOrientation = +2
note: ^--- here
Full Code, Live On Coliru
//#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/home/qi.hpp>
#include <fstream>
#include <sstream>
#include <iomanip>
namespace qi = boost::spirit::qi;
namespace Ast {
using Id = unsigned;
using Size = uint8_t;
using Coord = Size;
using ColorNumber = Size;
using Orientation = Size;
using Delta = signed;
struct Initialization {
Id id;
Coord row;
Coord col;
Orientation orientation;
};
struct Color {
Id id;
ColorNumber nextColor;
Delta deltaOrientation;
};
struct File {
Size numColors{}, boardSize{}, numSnails{};
std::vector<Initialization> initializations;
std::vector<Color> colors;
};
} // namespace Ast
BOOST_FUSION_ADAPT_STRUCT(Ast::Initialization, id, row, col, orientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::Color, id, nextColor, deltaOrientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::File, numColors, boardSize, numSnails,
initializations, colors)
template <typename It>
struct GameParser : qi::grammar<It, Ast::File()> {
GameParser() : GameParser::base_type(start) {
using namespace qi;
start = skip(blank)[file];
auto section = [](const std::string& name) {
return copy('[' >> lexeme[lit(name)] >> ']' >> (+eol | eoi));
};
auto required = [](const std::string& name, auto value) {
return copy(lexeme[eps > lit(name)] > '=' > value >
(+eol | eoi));
};
file =
required("numColors", _size) >
required("boardSize", _size) >
required("numSnails", _size) >
*initialization >
*color >
eoi; // must reach end of input
initialization = section("initialization") >
required("id", _id) >
required("row", _coord) >
required("col", _coord) >
required("orientation", _orientation);
color = section("color") >
required("id", _id) >
required("nextColor", _colorNumber) >
required("deltaOrientation", _delta);
BOOST_SPIRIT_DEBUG_NODES((file)(initialization)(color))
}
private:
using Skipper = qi::blank_type;
qi::rule<It, Ast::File()> start;
qi::rule<It, Ast::File(), Skipper> file;
qi::rule<It, Ast::Initialization(), Skipper> initialization;
qi::rule<It, Ast::Color(), Skipper> color;
qi::uint_parser<Ast::Id> _id;
qi::uint_parser<Ast::Size> _size;
qi::uint_parser<Ast::Coord> _coord;
qi::uint_parser<Ast::ColorNumber> _colorNumber;
qi::uint_parser<Ast::Orientation> _orientation;
qi::int_parser<Ast::Delta> _delta;
};
std::string read_file(const std::string& name) {
std::ifstream ifs(name);
return std::string(std::istreambuf_iterator<char>(ifs), {});
}
static Ast::File parse_game(std::string_view input) {
using SVI = std::string_view::const_iterator;
static const GameParser<SVI> parser{};
try {
Ast::File parsed;
if (qi::parse(input.begin(), input.end(), parser, parsed)) {
return parsed;
}
throw std::runtime_error("Unable to parse game");
} catch (qi::expectation_failure<SVI> const& ef) {
std::ostringstream oss;
auto where = ef.first - input.begin();
auto sol = 1 + input.find_last_of("\r\n", where);
auto lineno = 1 + std::count(input.begin(), input.begin() + sol, '\n');
auto col = 1 + where - sol;
auto llen = input.substr(sol).find_first_of("\r\n");
oss << "input.txt:" << lineno << ":" << col << " Expected: " << ef.what_ << "\n"
<< " note: " << input.substr(sol, llen) << "\n"
<< " note:" << std::setw(col) << "" << "^--- here";
throw std::runtime_error(oss.str());
}
}
int main() {
std::string game_save = read_file("input.txt");
try {
Ast::File data = parse_game(game_save);
} catch (std::exception const& e) {
std::cerr << e.what() << "\n";
}
}
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