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# nlohmann::basic_json::emplace_back

    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`.

## Template parameters

`Args`
  compatible types to create a `basic_json` object

## Parameters

`args` (in)
  arguments to forward to a constructor of `basic_json`

## Return value

reference to the inserted element

## Exceptions

Throws `type_error.311` when called on a type other than JSON array or `null`; example: `"cannot use emplace_back() with number"`

## Complexity

Amortized constant.

## Examples

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"]]

## Version history

- Since version 2.0.8.
- Returns reference since 3.7.0.

Last update: May 1, 2022
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