template<class... Args> reference emplace_back(Args&& ... args);
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.
Args : compatible types to create a basic_json object
By adding an element to the end of the array, a reallocation can happen, in which case all iterators (including the end() iterator) and all references to the elements are invalidated. Otherwise, only the end() iterator is invalidated.
args (in) : arguments to forward to a constructor of basic_json
reference to the inserted element
Throws type_error.311 when called on a type other than JSON array or null; example: "cannot use emplace_back() with number"
Amortized constant.
Example
The example shows how emplace_back() can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// create JSON values
json array = {1, 2, 3, 4, 5};
json null;
// print values
std::cout << array << '\n';
std::cout << null << '\n';
// add values
array.emplace_back(6);
null.emplace_back("first");
null.emplace_back(3, "second");
// print values
std::cout << array << '\n';
std::cout << null << '\n';
}
Output:
[1,2,3,4,5] null [1,2,3,4,5,6] ["first",["second","second","second"]]