json/docs/mkdocs/docs/api/basic_json/size.md

nlohmann::basic_json::size

size_type size() const noexcept;

Returns the number of elements in a JSON value.

Return value

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

Value type	return value
null	0
boolean	1
string	1
number	1
binary	1
object	result of function object_t::size()
array	result of function array_t::size()

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 size() functions have constant complexity.

Notes

This function does not return the length of a string stored as JSON value -- it returns the number of elements in the JSON value which is 1 in the case of a string.

Examples

??? example

The following code calls `size()` on the different value types.

```cpp
--8<-- "examples/size.cpp"
```

Output:

```json
--8<-- "examples/size.output"
```

See also

• empty checks whether the JSON value has no elements
• max_size returns the maximum possible number of elements
• basic_json_view::size - the same function on a zero-copy view

Version history

• Added in version 1.0.0.
• Extended to return 1 for binary types in version 3.8.0.