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nlohmann::basic_json::array_t

using array_t = ArrayType<basic_json, AllocatorType<basic_json>>;

The type used to store JSON arrays.

RFC 8259 describes JSON arrays as follows:

An array is an ordered sequence of zero or more values.

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
the allocator to use for objects (e.g., std::allocator)

Notes

Default type

With the default values for ArrayType (std::vector) and AllocatorType (std::allocator), the default value for array_t is:

std::vector<
  basic_json, // value_type
  std::allocator<basic_json> // allocator_type
>

Limits

RFC 8259 specifies:

An implementation may set limits on the maximum depth of nesting.

In this class, the array's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the max_size function of a JSON array.

Storage

Arrays are stored as pointers in a basic_json type. That is, for any access to array values, a pointer of type array_t* must be dereferenced.

Examples

Example

The following code shows that array_t is by default, a typedef to std::vector<nlohmann::json>.

#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    std::cout << std::boolalpha << std::is_same<std::vector<json>, json::array_t>::value << std::endl;
}

Output:

true

Version history

  • Added in version 1.0.0.

Last update: September 18, 2022