JSON for Modern C++  3.7.0

◆ emplace_back()

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>
template<class... Args>
reference nlohmann::basic_json::emplace_back ( Args &&...  args)
inline

Creates a JSON value from the passed parameters args to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending the value created from args.

Parameters
[in]argsarguments to forward to a constructor of basic_json
Template Parameters
Argscompatible types to create a basic_json object
Returns
reference to the inserted element
Exceptions
type_error.311when called on a type other than JSON array or null; example: "cannot use emplace_back() with number"
Complexity
Amortized constant.
Example
The example shows how push_back() can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.
1 #include <iostream>
2 #include <nlohmann/json.hpp>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create JSON values
9  json array = {1, 2, 3, 4, 5};
10  json null;
11 
12  // print values
13  std::cout << array << '\n';
14  std::cout << null << '\n';
15 
16  // add values
18  null.emplace_back("first");
19  null.emplace_back(3, "second");
20 
21  // print values
22  std::cout << array << '\n';
23  std::cout << null << '\n';
24 }
basic_json<> json
default JSON class
Definition: json.hpp:2355
static basic_json array(initializer_list_t init={})
explicitly create an array from an initializer list
Definition: json.hpp:15905
reference emplace_back(Args &&... args)
add an object to an array
Definition: json.hpp:19422

Output (play with this example online):
[1,2,3,4,5]
null
[1,2,3,4,5,6]
["first",["second","second","second"]]
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/emplace_back.cpp -o emplace_back 
Since
version 2.0.8, returns reference since 3.7.0

Definition at line 19422 of file json.hpp.