json/doc/mkdocs/docs/api/basic_json/empty.md

# basic_json::empty

```cpp
bool empty() const noexcept;
```

Checks if a JSON value has no elements (i.e. whether its [`size()`](size.md) is `0`).
    
## Return value

The return value depends on the different types and is defined as follows:

Value type  | return value
----------- | -------------
null        | `#!cpp true`
boolean     | `#!cpp false`
string      | `#!cpp false`
number      | `#!cpp false`
binary      | `#!cpp false`
object      | result of function `object_t::empty()`
array       | result of function `array_t::empty()`

## Exception safety

No-throw guarantee: this function never throws exceptions.

## Complexity

Constant, as long as [`array_t`](array_t.md) and [`object_t`](object_t.md) satisfy the
[Container](https://en.cppreference.com/w/cpp/named_req/Container) concept; that is, their `empty()` functions have
constant complexity.

## Possible implementation

```cpp
bool empty() const noexcept
{
    return size() == 0;
}
```

## Notes

This function does not return whether a string stored as JSON value is empty -- it returns whether the JSON container
itself is empty which is `#!cpp false` in the case of a string.

## Example

??? example

    The following code uses `empty()` to check if a JSON object contains any elements.
    
    ```cpp
    --8<-- "examples/empty.cpp"
    ```
    
    Output:
    
    ```json
    --8<-- "examples/empty.output"
    ```

## Version history

- Added in version 1.0.0.
- Extended to return `#!cpp false` for binary types in version 3.8.0.