api/basic_json/empty/index.md

# nlohmann::basic_json::empty

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

Checks if a JSON value has no elements (i.e., whether its [`size()`](https://json.nlohmann.me/api/basic_json/size/index.md) is `0`).

## Return value

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

| Value type | return value                           |
| ---------- | -------------------------------------- |
| null       | `true`                                 |
| boolean    | `false`                                |
| string     | `false`                                |
| number     | `false`                                |
| binary     | `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`](https://json.nlohmann.me/api/basic_json/array_t/index.md) and [`object_t`](https://json.nlohmann.me/api/basic_json/object_t/index.md) satisfy the [Container](https://en.cppreference.com/w/cpp/named_req/Container) concept; that is, their `empty()` functions have constant complexity.

## Possible implementation

```
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 `false` in the case of a string.

## Examples

Example

The following code uses `empty()` to check if a JSON object contains any elements.

```
#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    // create JSON values
    json j_null;
    json j_boolean = true;
    json j_number_integer = 17;
    json j_number_float = 23.42;
    json j_object = {{"one", 1}, {"two", 2}};
    json j_object_empty(json::value_t::object);
    json j_array = {1, 2, 4, 8, 16};
    json j_array_empty(json::value_t::array);
    json j_string = "Hello, world";

    // call empty()
    std::cout << std::boolalpha;
    std::cout << j_null.empty() << '\n';
    std::cout << j_boolean.empty() << '\n';
    std::cout << j_number_integer.empty() << '\n';
    std::cout << j_number_float.empty() << '\n';
    std::cout << j_object.empty() << '\n';
    std::cout << j_object_empty.empty() << '\n';
    std::cout << j_array.empty() << '\n';
    std::cout << j_array_empty.empty() << '\n';
    std::cout << j_string.empty() << '\n';
}
```

Output:

```
true
false
false
false
false
true
false
true
false
```

## Version history

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