JSON for Modern C++ 3.0

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~basic_json
| template<template< typename U, typename V, typename...Args > class ObjectType = std::map, template< typename U, typename...Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>
nlohmann::basic_json::basic_json | ( | list_init_t | init,
|  | bool | type_deduction = `true`,
|  | value_t | manual_type = `value_t::array`
| ) |  |
| inline
  Creates a JSON value of type array or object from the passed initializer list init. In case type_deduction is `true` (default), the type of the JSON value to be created is deducted from the initializer list init according to the following rules: If the list is empty, an empty JSON object value `{}` is created. If the list consists of pairs whose first element is a string, a JSON object value is created where the first elements of the pairs are treated as keys and the second elements are as values. In all other cases, an array is created. The rules aim to create the best fit between a C++ initializer list and JSON values. The ratioinale is as follows: The empty initializer list is written as `{}` which is exactly an empty JSON object. C++ has now way of describing mapped types other than to list a list of pairs. As JSON requires that keys must be of type string, rule 2 is the weakest constraint one can pose on initializer lists to interpret them as an object. In all other cases, the initializer list could not be interpreted as JSON object type, so interpreting it as JSON array type is safe. With the rules described above, the following JSON values cannot be expressed by an initializer list: the empty array (`[]`): use array(list_init_t) with an empty initializer list in this case arrays whose elements satisfy rule 2: use array(list_init_t) with the same initializer list in this case Note When used without parentheses around an empty initializer list, basic_json() is called instead of this function, yielding the JSON null value. Parameters
  [in] | init | initializer list with JSON values
  [in] | type_deduction | internal parameter; when set to `true`, the type of the JSON value is deducted from the initializer list init; when set to `false`, the type provided via manual_type is forced. This mode is used by the functions array(list_init_t) and object(list_init_t).
  [in] | manual_type | internal parameter; when type_deduction is set to `false`, the created JSON value will use the provided type (only value_t::array and value_t::object are valid); when type_deduction is set to `true`, this parameter has no effect
  Exceptions
  std::domain_error | if type_deduction is `false`, manual_type is `value_t::object`, but init contains an element which is not a pair whose first element is a string
  Complexity Linear in the size of the initializer list init. Example The example below shows how JSON values are created from initializer lists 1 #include <json.hpp> 2 3 using namespace nlohmann; 4 5 int main() 6 { 7 // create JSON values 8 json j_empty_init_list = json({}); 9 json j_object = { {"one", 1}, {"two", 2} }; 10 json j_array = {1, 2, 3, 4}; 11 json j_nested_object = { {"one", {1}}, {"two", {1, 2}} }; 12 json j_nested_array = { {{1}, "one"}, {{1, 2}, "two"} }; 13 14 // serialize the JSON value 15 std::cout << j_empty_init_list << '\n'; 16 std::cout << j_object << '\n'; 17 std::cout << j_array << '\n'; 18 std::cout << j_nested_object << '\n'; 19 std::cout << j_nested_array << '\n'; 20 } nlohmann::json basic_json<> json default JSON class Definition: json.hpp:6626 nlohmann::basic_json a class to store JSON values Definition: json.hpp:121 nlohmann namespace for Niels Lohmann Definition: json.hpp:56 Output:
      {}
      {"one":1,"two":2}
      [1,2,3,4]
      {"one":[1],"two":[1,2]}
      [[[1],"one"],[[1,2],"two"]]
  The example code above can be translated with
      g++ -std=c++11 -Isrc doc/examples/basic_json__list_init_t.cpp -o basic_json__list_init_t
. See also basic_json array(list_init_t) - create a JSON array value from an initializer list basic_json object(list_init_t) - create a JSON object value from an initializer list