How is nlohmann array_t different from Nlohmann json array? How is array_t actually used? The documentation for each is as follows.
Creates a JSON array value from a given initializer list. That is, given a list of values a, b, c, creates the JSON value [a, b, c]. If the initializer list is empty, the empty array [] is created.
Example,
nlohmann::json j_nonempty_init_list = json::array({1, 2, 3, 4});
std::cout << j_nonempty_init_list;
// [1,2,3,4]
To store objects in C++, a type is defined by the template parameters explained below.
- Template Parameters
- ArrayType container type to store arrays (e.g., std::vector or std::list)
- AllocatorType allocator to use for arrays (e.g., std::allocator)
json::array
is a static function that converts an initializer list into a json
value with internal type value_t::array
.
array_t
is defined as follows:
using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;
where ArrayType
is a template template parameter to 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 = std::int64_t,
class NumberUnsignedType = std::uint64_t,
class NumberFloatType = double,
template<typename U> class AllocatorType = std::allocator,
template<typename T, typename SFINAE = void> class JSONSerializer =
adl_serializer,
class BinaryType = std::vector<std::uint8_t>>
class basic_json;
and finally nlohmann::json
is just the default instantiation:
using json = basic_json<>;
So, json::array_t
is in the end a type alias for std::vector<json>
.
You can override the types passed to basic_json
if you create your own typedef over basic_json
.