Niels Lohmann
7b755737b4
From gregmarr's review of #5622: - count() counts every member with the key, so count(key) > 1 detects duplicate keys; it was contains() as 0/1 before. - get_to() passes types that get<T>() does not convert directly to from_json with the existing value, as basic_json::get_to() does, so that a from_json which sets only the fields present keeps the others. - array_index() checks the empty token and "-" first; the results are unchanged. - Docs: no "if an exception is thrown" where a view never changes anything; the borrowed source must also stay unmodified; items() on a temporary view is safe; back()/front() notes shortened; the basic_json see-also entries say how the view's results can differ. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2.1 KiB
nlohmann::basic_json_view::back
basic_json_view back() const;
Returns the last element of an array, the last member value of an object, or the value itself if it is primitive
(as for BasicJsonType::back(), a primitive value is a range of one element).
Return value
The last 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
Linear in the size of the array or object: unlike front(), which only ever looks at the first
element, back() has to walk every element to find where they end, since elements are not a fixed size in the
index.
Notes
Unlike BasicJsonType::back(), which has undefined behavior for an empty array or object,
back() 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 final status of a build log with `back()`. Even though `back()` is linear in
the number of events (unlike [`front()`](front.md), which is constant), it still avoids building a
`BasicJsonType` value for the events that are not needed.
```cpp
--8<-- "examples/basic_json_view__back.cpp"
```
Output:
```json
--8<-- "examples/basic_json_view__back.output"
```
See also
- front - access the first element
BasicJsonType::back- the corresponding function ofbasic_json
Version history
- Added in version 3.13.0.