Niels Lohmann
061c30310e
- API pages for basic_json_document and basic_json_view, one per member, and for the four aliases, each with an example - features/json_view.md: the problem the view solves, ownership and lifetime, what matches basic_json::parse() and what differs, and when to choose json, ordered_json, SAX, or the view - the examples show why one would use the view, not only how: borrowed vs. owned input, reading a few fields and materializing one subtree, reusing a document across many messages - registered in the mkdocs navigation, llms.txt, the docset, the exceptions page (out_of_range.416), architecture.md, the integration page, and the README; the yyjson credit is added to the README and license.md Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.8 KiB
1.8 KiB
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"
```
See also
- basic_json_view::empty - the same check on a zero-copy view
Version history
- Added in version 1.0.0.
- Extended to return
#!cpp falsefor binary types in version 3.8.0.