Niels Lohmann
172eba6e46
Add See also links in both directions between the concept pages (features, home, integration) and the API pages, write API links in code font, give every entry a comment after a dash, and show the callback event figure on the parser callbacks page. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.8 KiB
nlohmann::basic_json_view::front
basic_json_view front() const;
Returns the first element of an array, the first member value of an object, or the value itself if it is primitive
(as for BasicJsonType::front(), a primitive value is a range of one element).
Return value
The first element or member value. For a primitive value (number, string, boolean), the value itself.
Exception safety
Strong guarantee: there are no changes to the view or the document it refers to.
Exceptions
Throws invalid_iterator.214 if the view is
null or discarded, or if it is an empty array or object.
This exception does not carry a JSON_DIAGNOSTICS path: the view has no
BasicJsonType value to point at, so the exception is created without one, even if BasicJsonType was built with
JSON_DIAGNOSTICS enabled.
Complexity
Constant.
Notes
Unlike BasicJsonType::front(), which has undefined behavior for an empty array or
object, front() throws invalid_iterator.214 for an empty array, an empty object, a null value, or a discarded
view.
Examples
??? example
The example below reads only the earliest entry of a build log with `front()`, without materializing the rest
of the (possibly long) log.
```cpp
--8<-- "examples/basic_json_view__front.cpp"
```
Output:
```json
--8<-- "examples/basic_json_view__front.output"
```
See also
back- access the last elementBasicJsonType::front- the corresponding function ofbasic_json
Version history
- Added in version 3.13.0.