* 🔥 consolidate documentation
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2021-12-29 13:41:01 +01:00

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nlohmann::basic_json::empty

bool empty() const noexcept;

Checks if a JSON value has no elements (i.e. whether its size() 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 and object_t satisfy the 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 #!cpp false in the case of a string.

Examples

??? 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.

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