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Using boost :: karma to format latitude / longitude strings

I need to format the values doublein coordinate lines, which have a very specific format, "DDMMSS.SSX"where:

  • "DD" is the full degree
  • "MM" is full minutes.
  • "SS.SS" is seconds with a fraction
  • "X" means "N" or "S" depending on the hemisphere

Fields must be filled with zeros. Spaces cannot be accepted. Formatting examples:

47.2535 ==> "471512.45N"
-0.123345 ==> "000724.04S"

I managed to create the following program that does this work. However, I have a few questions:

  • Is there a more elegant way for a rule locls? The goal is to store the absolute value in a local variable value. Is there a (possibly more elegant) way to access a function fabs()?
  • In my opinion, assignments _1( _1 = _valetc.) are not needed since I have a value in a local variable value. However, if I delete these appointments, all I get is that "000000.00N".
  • the "workhorse" of this formatting is the int_ generator, which I use after calculating and translating the original value. Is there a better approach?
  • Is there any better solution to this kind of problem?

I would love some feedback

#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/bind.hpp>

namespace karma = boost::spirit::karma;

typedef std::back_insert_iterator<std::string> iterator_type;

struct genLongitude : karma::grammar<iterator_type, double()>
{
    genLongitude()
        :   genLongitude::base_type(start)
    {
        using karma::eps;
        using karma::int_;
        using karma::char_;
        using karma::_1;
        using karma::_val;
        using karma::right_align;
        using boost::phoenix::static_cast_;
        using boost::phoenix::ref;
        using boost::phoenix::if_;

        start = locls
                << degrees << minutes << seconds
                << ( eps(_val < 0.0) << char_('E') | char_('W')   );

        locls = eps[_1 = _val, if_(_val < 0.0) [ref(value) = - _val] .else_ [ref(value) = _val]];

        degrees = right_align(3,char_('0'))[int_[_1 = static_cast_<int>(ref(value))]]
                  << eps[ref(value) = (ref(value) - static_cast_<int>(ref(value))) * 60 ];

        minutes = right_align(2,char_('0'))[int_[_1 = static_cast_<int>(ref(value))]]
                  << eps[ref(value) = (ref(value) - static_cast_<int>(ref(value))) * 60 ];

        seconds = right_align(2,char_('0'))[int_[_1 = static_cast_<int>(ref(value))]]
                  << char_(".")
                  << eps[ref(value) = (ref(value) - static_cast_<int>(ref(value))) * 100 ]
                  << right_align(2,char_('0'))[int_[_1 = static_cast_<int>(ref(value))]];
    }

private:
    double value;

    karma::rule<iterator_type, double()>    start, locls, degrees, minutes, seconds;
};

int main()
{
    for(auto & value : std::vector<double>{ 47.25346, 13.984364, -0.1233453, -44.3 })
    {
        std::string generated;
        iterator_type outiter(generated);
        auto rv = karma::generate(outiter, genLatitude(), value);
        std::cout << "(" << rv << ") " << value << " ==> " << generated << std::endl;
    }
}

Update: , ( ) "DDMMSS.SSX", - "DDDMMSS.SSX". , -90 +90, - -180 +180.

+4
2

,

Q., , ?

Boost Format. LatLongRep - , IO-:

namespace manip {
    struct LatLongRepIO : LatLongRep {
        LatLongRepIO(double val, char const* choices) : LatLongRep(val), _display(choices) { }
      private:
        char const* _display;

        friend std::ostream& operator<<(std::ostream& os, LatLongRepIO const& llr) {
            return os << boost::format("%03d%02d%05.2f%c")
                        % llr._deg % llr._min % llr._sec 
                        % (llr._display[llr._hemi]);
        }
    };

    LatLongRepIO as_latitude (double val) { return { val, "WE" }; }
    LatLongRepIO as_longitude(double val) { return { val, "NS" }; }
}

Boost Spirit, Phoenix Fusion alltogether :

int main() {
    using namespace helpers::manip;

    for(double value : { 47.25346, 13.984364, -0.1233453, -44.3 })
        std::cout << as_latitude(value) << "\t" << as_longitude(value) << "\n";
}

DEMO

#include <boost/format.hpp>
#include <cmath>

namespace helpers {
    struct LatLongRep {
        bool _hemi; double _deg, _min, _sec;

        LatLongRep(double val) 
          : _hemi(0 < val),
            _min(60  * std::modf(std::abs(val), &_deg)),
            _sec(60  * std::modf(_min, &_min))
        { }
    };

    namespace manip {
        struct LatLongRepIO : LatLongRep {
            LatLongRepIO(double val, char const* choices) : LatLongRep(val), _display(choices) { }
          private:
            char const* _display;

            friend std::ostream& operator<<(std::ostream& os, LatLongRepIO const& llr) {
                return os << boost::format("%03d%02d%05.2f%c")
                            % llr._deg % llr._min % llr._sec 
                            % (llr._display[llr._hemi]);
            }
        };

        LatLongRepIO as_latitude (double val) { return { val, "WE" }; }
        LatLongRepIO as_longitude(double val) { return { val, "NS" }; }
    }
}

#include <iostream>

int main() {
    using namespace helpers::manip;

    for(double value : { 47.25346, 13.984364, -0.1233453, -44.3 })
        std::cout << as_latitude(value) << "\t" << as_longitude(value) << "\n";
}


0471512.46E  0471512.46S
0135903.71E  0135903.71S
0000724.04W  0000724.04N
0441760.00W  0441760.00N
+2

.

, , .

stateful, , .

, ( ) → (, , , ). , :

struct LatLongRep {
    bool _hemi; double _deg, _min, _sec;

    LatLongRep(double val) 
      : _hemi(0 < val),
        _min(60  * std::modf(std::abs(val), &_deg)),
        _sec(60  * std::modf(_min, &_min))
        { }
};

:

karma::rule<iterator_type, LatLongRep()> latitude, longitude;

:

    latitude =
            right_align(3, '0') [ uint_ ] 
         << right_align(2, '0') [ uint_ ] 
         << right_align(5, '0') [ seconds ]
         << east_west;

Demo

, :

Live On Coliru

#include <boost/spirit/include/karma.hpp>
#include <boost/fusion/adapted/struct.hpp>
#include <cmath>

namespace karma = boost::spirit::karma;

typedef std::back_insert_iterator<std::string> iterator_type;

struct LatLongRep {
    bool _hemi; double _deg, _min, _sec;

    LatLongRep(double val) 
      : _hemi(0 < val),
        _min(60  * std::modf(std::abs(val), &_deg)),
        _sec(60  * std::modf(_min, &_min))
        { }
};

BOOST_FUSION_ADAPT_STRUCT(LatLongRep, _deg, _min, _sec, _hemi)

struct genLatLong : karma::grammar<iterator_type, double()> {
    genLatLong() : genLatLong::base_type(start)
    {
        using namespace karma;

        east_west.add  (true, 'E')(false, 'W');
        north_south.add(true, 'N')(false, 'S');

        start    = latitude;

        latitude =
                right_align(3, '0') [ uint_ ] 
             << right_align(2, '0') [ uint_ ] 
             << right_align(5, '0') [ seconds ]
             << east_west;

        longitude =
                right_align(3, '0') [ uint_ ] 
             << right_align(2, '0') [ uint_ ] 
             << right_align(5, '0') [ seconds ]
             << north_south;
    }

private:
    struct secfmt : karma::real_policies<double> {
        unsigned precision(double)      const { return 2;    }
        bool     trailing_zeros(double) const { return true; }
    };
    karma::real_generator<double, secfmt>    seconds;

    karma::symbols<bool, char> east_west, north_south;
    karma::rule<iterator_type, double()>     start;
    karma::rule<iterator_type, LatLongRep()> latitude, longitude;
};

int main()
{
    genLatLong const gen;

    for(auto & value : std::vector<double>{ 47.25346, 13.984364, -0.1233453, -44.3 })
    {
        std::string generated;
        iterator_type outiter(generated);
        auto rv = karma::generate(outiter, gen, value);
        std::cout << "(" << std::boolalpha << rv << ") " << value << " ==> " << generated << std::endl;
    }
}


(true) 47.2535 ==> 0471512.46E
(true) 13.9844 ==> 0135903.71E
(true) -0.123345 ==> 0000724.04W
(true) -44.3 ==> 0441760.00W

/:

  • real_policy secfmt ; .

  • , LatLongRep / Phoenix (. ). . Boost Spirit: " - ",

  • karma::symbols<> :

    karma::symbols<bool, char> east_west, north_south;
east_west.add  (true, 'E')(false, 'W');
north_south.add(true, 'N')(false, 'S');

  • ,

  • , , ,

+5

Source: https://habr.com/ru/post/1607404/

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