JSON for Modern C++  2.1.1

◆ 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>
void 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
Exceptions
std::domain_errorwhen 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 <json.hpp>
2 
3 using json = nlohmann::json;
4 
5 int main()
6 {
7  // create JSON values
8  json array = {1, 2, 3, 4, 5};
9  json null;
10 
11  // print values
12  std::cout << array << '\n';
13  std::cout << null << '\n';
14 
15  // add values
16  array.emplace_back(6);
17  null.emplace_back("first");
18  null.emplace_back(3, "second");
19 
20  // print values
21  std::cout << array << '\n';
22  std::cout << null << '\n';
23 }
basic_json<> json
default JSON class
Definition: json.hpp:12369
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 -Isrc doc/examples/emplace_back.cpp -o emplace_back 
Since
version 2.0.8

Definition at line 5444 of file json.hpp.