json/docs/mkdocs/docs/api/basic_json/emplace_back.md

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 #!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 #!json 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.
    
```cpp
--8<-- "examples/emplace_back.cpp"
```

Output:

```json
--8<-- "examples/emplace_back.output"
```

Version history

• Since version 2.0.8.
• Returns reference since 3.7.0.