1# basic_json::emplace_back 2 3```cpp 4template<class... Args> 5reference emplace_back(Args&& ... args); 6``` 7 8Creates a JSON value from the passed parameters `args` to the end of the JSON value. If the function is called on a JSON 9`#!json null` value, an empty array is created before appending the value created from `args`. 10 11## Template parameters 12 13`Args` 14: compatible types to create a `basic_json` object 15 16## Parameters 17 18`args` (in) 19: arguments to forward to a constructor of `basic_json` 20 21## Return value 22 23reference to the inserted element 24 25## Exceptions 26 27Throws [`type_error.311`](../../home/exceptions.md#jsonexceptiontype_error311) when called on a type other than JSON 28array or `#!json null`; example: `"cannot use emplace_back() with number"` 29 30## Complexity 31 32Amortized constant. 33 34## Examples 35 36??? example 37 38 The example shows how `emplace_back()` can be used to add elements to a JSON array. Note how the `null` value was 39 silently converted to a JSON array. 40 41 ```cpp 42 --8<-- "examples/emplace_back.cpp" 43 ``` 44 45 Output: 46 47 ```json 48 --8<-- "examples/emplace_back.output" 49 ``` 50 51## Version history 52 53- Since version 2.0.8. 54- Returns reference since 3.7.0. 55