The csv extension implements decode from and encode to the CSV format
For the examples below you need to include some header files and initialize a string of CSV data:
#include <iomanip>
#include <iostream>
#include <jsoncons/json.hpp>
#include <jsoncons_ext/csv/csv.hpp>
const std::string data = R"(index_id,observation_date,rate
EUR_LIBOR_06M,2015-10-23,0.0000214
EUR_LIBOR_06M,2015-10-26,0.0000143
EUR_LIBOR_06M,2015-10-27,0.0000001
)";jsoncons allows you to work with the CSV data similarly to JSON data:
-
As a variant-like data structure, basic_json
-
As a strongly typed C++ data structure that implements json_type_traits
-
With cursor-level access to a stream of parse events
int main()
{
auto options = csv::csv_options{}
.assume_header(true);
// Parse the CSV data into an ojson value
ojson j = csv::decode_csv<ojson>(data, options);
// Pretty print
auto print_options = json_options{}
.float_format(float_chars_format::fixed);
std::cout << "(1)\n" << pretty_print(j, print_options) << "\n\n";
// Iterate over the rows
std::cout << "(2)\n";
for (const auto& row : j.array_range())
{
// Access rated as string and rating as double
std::cout << row["index_id"].as<std::string>() << ", "
<< row["observation_date"].as<std::string>() << ", "
<< row["rate"].as<double>() << "\n";
}
}Output:
(1)
[
{
"index_id": "EUR_LIBOR_06M",
"observation_date": "2015-10-23",
"rate": 0.0000214
},
{
"index_id": "EUR_LIBOR_06M",
"observation_date": "2015-10-26",
"rate": 0.0000143
},
{
"index_id": "EUR_LIBOR_06M",
"observation_date": "2015-10-27",
"rate": 0.0000001
}
]
(2)
EUR_LIBOR_06M, 2015-10-23, 0.0000214
EUR_LIBOR_06M, 2015-10-26, 0.0000143
EUR_LIBOR_06M, 2015-10-27, 0.0000001
jsoncons supports transforming CSV data into C++ data structures. The functions decode_csv and encode_csv convert strings or streams of CSV data to C++ data structures and back. Decode and encode work for all C++ classes that have json_type_traits defined. jsoncons already supports many types in the standard library, and your own types will be supported too if you specialize json_type_traits in the jsoncons namespace.
#include <boost/date_time/gregorian/gregorian.hpp>
namespace ns {
class fixing
{
std::string index_id_;
boost::gregorian::date observation_date_;
double rate_;
public:
fixing(const std::string& index_id, boost::gregorian::date observation_date, double rate)
: index_id_(index_id), observation_date_(observation_date), rate_(rate)
{
}
const std::string& index_id() const {return index_id_;}
boost::gregorian::date observation_date() const {return observation_date_;}
double rate() const {return rate_;}
};
} // namespace ns
template <typename Json>
struct json_type_traits<Json,boost::gregorian::date>
{
static bool is(const Json& val) noexcept
{
if (!val.is_string())
return false;
try
{
std::string s = val.template as<std::string>();
boost::gregorian::from_simple_string(s);
return true;
}
catch (...)
{
return false;
}
}
static boost::gregorian::date as(const Json& val)
{
std::string s = val.template as<std::string>();
return boost::gregorian::from_simple_string(s);
}
static Json to_json(boost::gregorian::date val,
Json::allocator_type alloc = Json::allocator_type())
{
return Json(to_iso_extended_string(val), alloc);
}
};
JSONCONS_ALL_CTOR_GETTER_TRAITS(ns::fixing, index_id, observation_date, rate)
int main()
{
auto options = csv::csv_options{}
.assume_header(true)
.float_format(float_chars_format::fixed);
// Decode the CSV data into a c++ structure
std::vector<ns::fixing> v = csv::decode_csv<std::vector<ns::fixing>>(data, options);
// Iterate over values
std::cout << std::fixed << std::setprecision(7);
std::cout << "(1)\n";
for (const auto& item : v)
{
std::cout << item.index_id() << ", " << item.observation_date() << ", " << item.rate() << "\n";
}
// Encode the c++ structure into CSV data
std::string s;
csv::encode_csv(v, s, options);
std::cout << "(2)\n";
std::cout << s << "\n";
}Output:
(1)
EUR_LIBOR_06M, 2015-10-23, 0.0000214
EUR_LIBOR_06M, 2015-10-26, 0.0000143
EUR_LIBOR_06M, 2015-10-27, 0.0000001
(2)
index_id,observation_date,rate
EUR_LIBOR_06M,2015-10-23,0.0000214
EUR_LIBOR_06M,2015-10-26,0.0000143
EUR_LIBOR_06M,2015-10-27,0.0000001
int main()
{
auto options = csv::csv_options{}
.assume_header(true);
csv::csv_string_cursor cursor(data, options);
for (; !cursor.done(); cursor.next())
{
const auto& event = cursor.current();
switch (event.event_type())
{
case staj_event_type::begin_array:
std::cout << event.event_type() << " " << "\n";
break;
case staj_event_type::end_array:
std::cout << event.event_type() << " " << "\n";
break;
case staj_event_type::begin_object:
std::cout << event.event_type() << " " << "\n";
break;
case staj_event_type::end_object:
std::cout << event.event_type() << " " << "\n";
break;
case staj_event_type::key:
// Or std::string_view, if supported
std::cout << event.event_type() << ": " << event.get<jsoncons::string_view>() << "\n";
break;
case staj_event_type::string_value:
// Or std::string_view, if supported
std::cout << event.event_type() << ": " << event.get<jsoncons::string_view>() << "\n";
break;
case staj_event_type::null_value:
std::cout << event.event_type() << "\n";
break;
case staj_event_type::bool_value:
std::cout << event.event_type() << ": " << std::boolalpha << event.get<bool>() << "\n";
break;
case staj_event_type::int64_value:
std::cout << event.event_type() << ": " << event.get<int64_t>() << "\n";
break;
case staj_event_type::uint64_value:
std::cout << event.event_type() << ": " << event.get<uint64_t>() << "\n";
break;
case staj_event_type::double_value:
std::cout << event.event_type() << ": " << event.get<double>() << "\n";
break;
default:
std::cout << "Unhandled event type: " << event.event_type() << " " << "\n";
break;
}
}
}Output:
begin_array
begin_object
key: index_id
string_value: EUR_LIBOR_06M
key: observation_date
string_value: 2015-10-23
key: rate
double_value: 0.0000214
end_object
begin_object
key: index_id
string_value: EUR_LIBOR_06M
key: observation_date
string_value: 2015-10-26
key: rate
double_value: 0.0000143
end_object
begin_object
key: index_id
string_value: EUR_LIBOR_06M
key: observation_date
string_value: 2015-10-27
key: rate
double_value: 0.0000001
end_object
end_array
You can use a staj_array_iterator to group the CSV parse events into basic_json records:
int main()
{
auto options = csv::csv_options{}
.assume_header(true);
csv::csv_string_cursor cursor(data, options);
auto view = staj_array<ojson>(cursor);
auto print_options = json_options{}
.float_format(float_chars_format::fixed);
for (const auto& item : view)
{
std::cout << pretty_print(item, print_options) << "\n";
}
}Output:
{
"index_id": "EUR_LIBOR_06M",
"observation_date": "2015-10-23",
"rate": 0.0000214
}
{
"index_id": "EUR_LIBOR_06M",
"observation_date": "2015-10-26",
"rate": 0.0000143
}
{
"index_id": "EUR_LIBOR_06M",
"observation_date": "2015-10-27",
"rate": 0.0000001
}
Or into strongly typed records:
int main()
{
using record_type = std::tuple<std::string,std::string,double>;
auto options = csv::csv_options{}
.assume_header(true);
csv::csv_string_cursor cursor(data, options);
auto view = staj_array<record_type>(cursor);
std::cout << std::fixed << std::setprecision(7);
for (const auto& record : view)
{
std::cout << std::get<0>(record) << ", " << std::get<1>(record) << ", " << std::get<2>(record) << "\n";
}
}Output
EUR_LIBOR_06M, 2015-10-23, 0.0000214
EUR_LIBOR_06M, 2015-10-26, 0.0000143
EUR_LIBOR_06M, 2015-10-27, 0.0000001