CSV (Comma Separated Values)

Glaze supports CSV reading and writing for structs and standard map types.

By default Glaze writes out structures row-wise, which is more efficient if all the data is available at once. Column-wise CSV format is also supported.

Note that if you want containers to have their CSV data aligned, they need to be the same length.

API

glz::read_csv(obj, buffer); // row-wise 
glz::read_csv<glz::colwise>(obj, buffer); // column-wise

glz::write_csv(obj, buffer); // row-wise
glz::write_csv<glz::colwise>(obj, buffer); // column-wise

Example

struct my_struct
{
   std::vector<int> num1{};
   std::deque<float> num2{};
   std::vector<bool> maybe{};
   std::vector<std::array<int, 3>> v3s{};
};

Reading/Writing column-wise:

std::string input_col =
       R"(num1,num2,maybe,v3s[0],v3s[1],v3s[2]
11,22,1,1,1,1
33,44,1,2,2,2
55,66,0,3,3,3
77,88,0,4,4,4)";

    my_struct obj{};

    expect(!glz::read_csv<glz::colwise>(obj, input_col));

    expect(obj.num1[0] == 11);
    expect(obj.num2[2] == 66);
    expect(obj.maybe[3] == false);
    expect(obj.v3s[0] == std::array{1, 1, 1});
    expect(obj.v3s[1] == std::array{2, 2, 2});
    expect(obj.v3s[2] == std::array{3, 3, 3});
    expect(obj.v3s[3] == std::array{4, 4, 4});

    std::string out{};

    expect(!glz::write<glz::opts{.format = glz::csv, .layout = glz::colwise}>(obj, out));
    expect(out ==
           R"(num1,num2,maybe,v3s[0],v3s[1],v3s[2]
11,22,1,1,1,1
33,44,1,2,2,2
55,66,0,3,3,3
77,88,0,4,4,4
)");

    expect(!glz::write_file_csv<glz::colwise>(obj, "csv_test_colwise.csv", std::string{}));

Headerless CSV for Struct Vectors

You can read and write vectors of structs without headers by disabling headers in opts_csv.

struct data_point { int id; float value; std::string name; };

std::vector<data_point> vec = {
  {1, 10.5f, "Point A"},
  {2, 20.3f, "Point B"}
};

std::string out;
glz::write<glz::opts_csv{.use_headers = false}>(vec, out);
// out:
// 1,10.5,Point A\n
// 2,20.3,Point B\n

std::vector<data_point> back;
glz::read<glz::opts_csv{.use_headers = false}>(back, out);

Notes: - Fields are in declaration order when use_headers = false. - You can also parse CSV that contains a header row by skipping it:

glz::read<glz::opts_csv{
  .use_headers = false,
  .skip_header_row = true
}>(back, headered_csv_string);

2D Arrays (matrix-style CSV)

Glaze supports reading and writing 2D arrays such as std::vector<std::vector<T>>:

Row-wise (default):

std::string csv = "1,2,3\n4,5,6\n";
std::vector<std::vector<int>> m;
glz::read<glz::opts_csv{.use_headers = false}>(m, csv);
// m == {{1,2,3},{4,5,6}}

std::string out2;
glz::write<glz::opts_csv{.use_headers = false}>(m, out2);

Column-wise (transpose on IO):

std::vector<std::vector<int>> cols = {{1,4},{2,5},{3,6}}; // 3 columns
std::string out;
glz::write<glz::opts_csv{.layout = glz::colwise, .use_headers = false}>(cols, out);
// out is row-wise CSV: 1,2,3\n4,5,6\n

std::vector<std::vector<int>> back;
glz::read<glz::opts_csv{.layout = glz::colwise, .use_headers = false}>(back, out);
// back == cols

Options: - skip_header_row — skip the first row when reading (useful when ingesting headered CSV into 2D arrays without using headers). - validate_rectangular — enforce equal column counts across rows on read. - On failure, read returns constraint_violated and sets a message in ctx.custom_error_message.

CSV Quoting and Special Values

• Strings and chars are quoted when needed; embedded quotes are escaped by doubling them.
• Quoted fields preserve commas, quotes, and newlines (handles both \n and \r\n).
• Empty fields are parsed as default values (e.g., 0 for numbers, empty string for strings, false for booleans).
• Booleans accept true/false (case-insensitive) and 0/1; empty boolean fields default to false.

Examples:

std::vector<std::string> row = {"Normal", "Has,comma", "Has \"quotes\"", "Multi\nline"};
std::vector<std::vector<std::string>> m = {row};
std::string out;
glz::write<glz::opts_csv{.use_headers = false}>(m, out);
// out contains properly quoted and escaped CSV

std::vector<std::vector<std::string>> back;
glz::read<glz::opts_csv{.use_headers = false}>(back, out);

Choosing the Options API

For CSV, prefer opts_csv to access CSV-specific options:

glz::write<glz::opts_csv{.layout = glz::colwise, .use_headers = false}>(obj, out);
glz::read<glz::opts_csv{.use_headers = false, .skip_header_row = true}>(obj, in);

The helper convenience functions (read_csv, write_csv) remain available for basic cases.