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jsoncons::csv::basic_csv_reader

#include <jsoncons_ext/csv/csv_reader.hpp>

template<
    class CharT,
    class Source=jsoncons::stream_source<CharT>,
    class TempAllocator=std::allocator<char>>
class basic_csv_reader

The basic_csv_reader class reads a CSV file and produces JSON parse events.

basic_csv_reader is noncopyable and nonmoveable.

A number of specializations for common character types are defined:

Type Definition
csv_string_reader basic_csv_string_reader<char,string_source<char>> (since 0.164.0)
wcsv_stringreader basic_csv_string_reader<wchar_t,string_source<wchar_t>> (since 0.164.0)
csv_stream_reader basic_csv_stream_reader<char,stream_source<char>> (since 0.164.0)
wcsv_stream_reader basic_csv_stream_reader<wchar_t,stream_source<wchar_t>> (since 0.164.0)
csv_reader Constructible from either a string or stream (deprecated since 0.164.0)
wcsv_reader Constructible from either a wide character string or stream (deprecated since 0.164.0)

Member types

Type Definition
char_type CharT
source_type Source

Constructors

template <class Sourceable>
basic_csv_reader(Sourceable&& source,
                 basic_json_visitor<CharT>& visitor, 
                 const TempAllocator& alloc = TempAllocator()); (1)


template <class Sourceable>
basic_csv_reader(Sourceable&& source,
                 basic_json_visitor<CharT>& visitor,
                 const basic_csv_options<CharT>& options, 
                 const TempAllocator& alloc = TempAllocator()); (2)

template <class Sourceable>
basic_csv_reader(Sourceable&& source,
                 basic_json_visitor<CharT>& visitor,
                 std::function<bool(csv_errc,const ser_context&)> err_handler, 
                 const TempAllocator& alloc = TempAllocator()); (3)

template <class Sourceable>
basic_csv_reader(Sourceable&& source,
                 basic_json_visitor<CharT>& visitor,
                 const basic_csv_options<CharT>& options,
                 std::function<bool(csv_errc,const ser_context&)> err_handler, 
                 const TempAllocator& alloc = TempAllocator()); (4)

(1) Constructs a basic_csv_reader that reads from a character sequence or stream source and a basic_json_visitor that receives JSON events. Uses default basic_csv_options.

(2) Constructs a basic_csv_reader that that reads from a character sequence or stream source, a basic_json_visitor that receives JSON events, and basic_csv_options.

(3) Constructs a basic_csv_reader that reads from a character sequence or stream source, a basic_json_visitor that receives JSON events and the specified JSON parsing error handling. Uses default basic_csv_options.

(4) Constructs a basic_csv_reader that reads from a character sequence or stream source, a basic_json_visitor that receives JSON events, basic_csv_options, and the specified JSON parsing error handling.

Note: It is the programmer's responsibility to ensure that basic_csv_reader does not outlive any source or visitor passed in the constuctor, as basic_csv_reader holds pointers to but does not own these resources.

Parameters

source - a value from which a jsoncons::basic_string_view<char_type> is constructible, or a value from which a source_type is constructible. In the case that a jsoncons::basic_string_view<char_type> is constructible from source, source is dispatched immediately to the parser. Otherwise, the basic_csv_reader reads from a source_type in chunks.

Member functions

bool eof() const

Returns true when there is no more data to be read from the stream, false otherwise

void read()

Reports JSON related events for JSON objects, arrays, object members and array elements to a basic_json_visitor, such as a json_decoder. Throws a ser_error if parsing fails.

Examples

Reading a comma delimted file into an array of json values

Comma delimited input file

country_code,name
ABW,ARUBA
ATF,"FRENCH SOUTHERN TERRITORIES, D.R. OF"
VUT,VANUATU
WLF,WALLIS & FUTUNA ISLANDS

Note

  • The first record contains a header line, but we're going to ignore that and read the entire file as an array of arrays.
  • The third record has a field value that contains an embedded comma, so it must be quoted.

Code

std::string in_file = "countries.csv";
std::ifstream is(in_file);

json_decoder<json> decoder;

csv_stream_reader reader(is,decoder);
reader.read();
json countries = decoder.get_result();

std::cout << pretty_print(countries) << std::endl;

Output

[
    ["country_code","name"],
    ["ABW","ARUBA"],
    ["ATF","FRENCH SOUTHERN TERRITORIES, D.R. OF"],
    ["VUT","VANUATU"],
    ["WLF","WALLIS & FUTUNA ISLANDS"]
]

Reading a tab delimted file into an array of json objects

Tab delimited input file

employee-no employee-name   dept    salary  note
00000001    Smith, Matthew  sales   150,000.00      
00000002    Brown, Sarah    sales   89,000.00       
00000003    Oberc, Scott    finance 110,000.00      
00000004    Scott, Colette  sales   75,000.00       """Exemplary"" employee
Dependable, trustworthy"

Note

  • The first record is a header line, which will be used to associate data values with names
  • The fifth record has a field value that contains embedded quotes and a new line character, so it must be quoted and the embedded quotes escaped.

Code

std::string in_file = "employees.txt";
std::ifstream is(in_file);

json_decoder<json> decoder;
csv_options options;
options.field_delimiter = '\t'
       .assume_header = true;

csv_stream_reader reader(is,decoder,options);
reader.read();
json employees = decoder.get_result();

std::cout << pretty_print(employees) << std::endl;

Output

[
    {
        "dept":"sales",
        "employee-name":"Smith, Matthew",
        "employee-no":"00000001",
        "note":"",
        "salary":"150,000.00"
    },
    {
        "dept":"sales",
        "employee-name":"Brown, Sarah",
        "employee-no":"00000002",
        "note":"",
        "salary":"89,000.00"
    },
    {
        "dept":"finance",
        "employee-name":"Oberc, Scott",
        "employee-no":"00000003",
        "note":"",
        "salary":"110,000.00"
    },
    {
        "dept":"sales",
        "employee-name":"Scott, Colette",
        "employee-no":"00000004",
        "note":"\"Exemplary\" employee\nDependable, trustworthy",
        "salary":"75,000.00"
    }
]

Reading the comma delimited file as an array of objects with user supplied columns names

Note

  • The first record contains a header line, but we're going to ignore that and use our own names for the fields.

Code

std::string in_file = "countries.csv";
std::ifstream is(in_file);

json_decoder<json> decoder;

csv_options options;
options.column_names("Country Code,Name")
      .header_lines(1);

csv_stream_reader reader(is,decoder,options);
reader.read();
json countries = decoder.get_result();

std::cout << pretty_print(countries) << std::endl;

Output

[
    {
        "Country Code":"ABW",
        "Name":"ARUBA"
    },
    {
        "Country Code":"ATF",
        "Name":"FRENCH SOUTHERN TERRITORIES, D.R. OF"
    },
    {
        "Country Code":"VUT",
        "Name":"VANUATU"
    },
    {
        "Country Code":"WLF",
        "Name":"WALLIS & FUTUNA ISLANDS"
    }
]

Reading a comma delimited file with different mapping strategies

Input

Date,1Y,2Y,3Y,5Y
2017-01-09,0.0062,0.0075,0.0083,0.011
2017-01-08,0.0063,0.0076,0.0084,0.0112
2017-01-08,0.0063,0.0076,0.0084,0.0112

Code

json_decoder<ojson> decoder;
csv_options options;
options.assume_header(true)
       .column_types("string,float,float,float,float");

options.mapping_kind(csv_mapping_kind::n_rows);
std::istringstream is1("bond_yields.csv");
csv_stream_reader reader1(is1,decoder,options);
reader1.read();
ojson val1 = decoder.get_result();
std::cout << "\n(1)\n"<< pretty_print(val1) << "\n";

options.mapping_kind(csv_mapping_kind::n_objects);
std::istringstream is2("bond_yields.csv");
csv_stream_reader reader2(is2,decoder,options);
reader2.read();
ojson val2 = decoder.get_result();
std::cout << "\n(2)\n"<< pretty_print(val2) << "\n";

options.mapping_kind(csv_mapping_kind::m_columns);
std::istringstream is3("bond_yields.csv");
csv_stream_reader reader3(is3, decoder, options);
reader3.read();
ojson val3 = decoder.get_result();
std::cout << "\n(3)\n" << pretty_print(val3) << "\n";

Output

(1)
[
    ["Date","1Y","2Y","3Y","5Y"],
    ["2017-01-09",0.0062,0.0075,0.0083,0.011],
    ["2017-01-08",0.0063,0.0076,0.0084,0.0112],
    ["2017-01-08",0.0063,0.0076,0.0084,0.0112]
]

(2)
[
    {
        "Date": "2017-01-09",
        "1Y": 0.0062,
        "2Y": 0.0075,
        "3Y": 0.0083,
        "5Y": 0.011
    },
    {
        "Date": "2017-01-08",
        "1Y": 0.0063,
        "2Y": 0.0076,
        "3Y": 0.0084,
        "5Y": 0.0112
    },
    {
        "Date": "2017-01-08",
        "1Y": 0.0063,
        "2Y": 0.0076,
        "3Y": 0.0084,
        "5Y": 0.0112
    }
]

(3)
{
    "Date": ["2017-01-09","2017-01-08","2017-01-08"],
    "1Y": [0.0062,0.0063,0.0063],
    "2Y": [0.0075,0.0076,0.0076],
    "3Y": [0.0083,0.0084,0.0084],
    "5Y": [0.011,0.0112,0.0112]
}

Convert CSV to json when last column repeats

int main()
{
    const std::string bond_yields = R"(Date,Yield
2017-01-09,0.0062,0.0075,0.0083,0.011,0.012
2017-01-08,0.0063,0.0076,0.0084,0.0112,0.013
2017-01-08,0.0063,0.0076,0.0084,0.0112,0.014
)";

    // array of arrays
    json_decoder<ojson> decoder1;
    csv_options options1;
    options1.header_lines(1);
    options1.assume_header(false);
    options1.column_types("string,float*");
    std::istringstream is1(bond_yields);
    csv_stream_reader reader1(is1, decoder1, options1);
    reader1.read();
    ojson val1 = decoder1.get_result();
    std::cout << "\n(1)\n" << pretty_print(val1) << "\n";

    // array of objects
    json_decoder<ojson> decoder2;
    csv_options options2;
    options2.assume_header(true);
    options2.column_types("string,[float*]");
    std::istringstream is2(bond_yields);
    csv_stream_reader reader2(is2, decoder2, options2);
    reader2.read();
    ojson val2 = decoder2.get_result();
    std::cout << "\n(2)\n" << pretty_print(val2) << "\n";
}

Output:

(1)
[
    ["2017-01-09",0.0062,0.0075,0.0083,0.011,0.012],
    ["2017-01-08",0.0063,0.0076,0.0084,0.0112,0.013],
    ["2017-01-08",0.0063,0.0076,0.0084,0.0112,0.014]
]

(2)
[
    {
        "Date": "2017-01-09",
        "Yield": [0.0062,0.0075,0.0083,0.011,0.012]
    },
    {
        "Date": "2017-01-08",
        "Yield": [0.0063,0.0076,0.0084,0.0112,0.013]
    },
    {
        "Date": "2017-01-08",
        "Yield": [0.0063,0.0076,0.0084,0.0112,0.014]
    }
]

Convert CSV to json when last two columns repeat

const std::string holidays = R"(1,CAD,2,UK,3,EUR,4,US + UK,5,US
38719,2-Jan-2006,40179,1-Jan-2010,38719,2-Jan-2006,38719,2-Jan-2006,39448,1-Jan-2008
38733,16-Jan-2006,40270,2-Apr-2010,38733,16-Jan-2006,38733,16-Jan-2006,39468,21-Jan-2008
)";

    json_decoder<ojson> decoder;
    csv_options options;
    options.column_types("[integer,string]*");

    // Default
    std::istringstream is1(holidays);
    csv_stream_reader reader1(is1, decoder, options);
    reader1.read();
    ojson val1 = decoder.get_result();
    std::cout << pretty_print(val1) << "\n";

Output:

[
    [
        [1,"CAD"],
        [2,"UK"],
        [3,"EUR"],
        [4,"US + UK"],
        [5,"US"]
    ],
    [
        [38719,"2-Jan-2006"],
        [40179,"1-Jan-2010"],
        [38719,"2-Jan-2006"],
        [38719,"2-Jan-2006"],
        [39448,"1-Jan-2008"]
    ],
    [
        [38733,"16-Jan-2006"],
        [40270,"2-Apr-2010"],
        [38733,"16-Jan-2006"],
        [38733,"16-Jan-2006"],
        [39468,"21-Jan-2008"]
    ]
]