JSON for Modern C++  3.7.2

◆ array()

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>
static basic_json nlohmann::basic_json::array ( initializer_list_t  init = {})

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.

This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (basic_json(initializer_list_t, bool, value_t)). These cases are:
  1. creating an array whose elements are all pairs whose first element is a string – in this case, the initializer list constructor would create an object, taking the first elements as keys
  2. creating an empty array – passing the empty initializer list to the initializer list constructor yields an empty object
[in]initinitializer list with JSON values to create an array from (optional)
JSON array value
Linear in the size of init.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
The following code shows an example for the array function.
1 #include <iostream>
2 #include <nlohmann/json.hpp>
4 using json = nlohmann::json;
6 int main()
7 {
8  // create JSON arrays
9  json j_no_init_list = json::array();
10  json j_empty_init_list = json::array({});
11  json j_nonempty_init_list = json::array({1, 2, 3, 4});
12  json j_list_of_pairs = json::array({ {"one", 1}, {"two", 2} });
14  // serialize the JSON arrays
15  std::cout << j_no_init_list << '\n';
16  std::cout << j_empty_init_list << '\n';
17  std::cout << j_nonempty_init_list << '\n';
18  std::cout << j_list_of_pairs << '\n';
19 }

Output (play with this example online):
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/array.cpp -o array 
See also
basic_json(initializer_list_t, bool, value_t) – create a JSON value from an initializer list
object(initializer_list_t) – create a JSON object value from an initializer list
version 1.0.0

Definition at line 16091 of file json.hpp.

static basic_json array(initializer_list_t init={})
explicitly create an array from an initializer list
Definition: json.hpp:16091
basic_json<> json
default JSON class
Definition: json.hpp:2445