1# basic_json::empty 2 3```cpp 4bool empty() const noexcept; 5``` 6 7Checks if a JSON value has no elements (i.e. whether its [`size()`](size.md) is `0`). 8 9## Return value 10 11The return value depends on the different types and is defined as follows: 12 13Value type | return value 14----------- | ------------- 15null | `#!cpp true` 16boolean | `#!cpp false` 17string | `#!cpp false` 18number | `#!cpp false` 19binary | `#!cpp false` 20object | result of function `object_t::empty()` 21array | result of function `array_t::empty()` 22 23## Exception safety 24 25No-throw guarantee: this function never throws exceptions. 26 27## Complexity 28 29Constant, as long as [`array_t`](array_t.md) and [`object_t`](object_t.md) satisfy the 30[Container](https://en.cppreference.com/w/cpp/named_req/Container) concept; that is, their `empty()` functions have 31constant complexity. 32 33## Possible implementation 34 35```cpp 36bool empty() const noexcept 37{ 38 return size() == 0; 39} 40``` 41 42## Notes 43 44This function does not return whether a string stored as JSON value is empty -- it returns whether the JSON container 45itself is empty which is `#!cpp false` in the case of a string. 46 47## Example 48 49??? example 50 51 The following code uses `empty()` to check if a JSON object contains any elements. 52 53 ```cpp 54 --8<-- "examples/empty.cpp" 55 ``` 56 57 Output: 58 59 ```json 60 --8<-- "examples/empty.output" 61 ``` 62 63## Version history 64 65- Added in version 1.0.0. 66- Extended to return `#!cpp false` for binary types in version 3.8.0. 67