Niels Lohmann
08dcdaf9b8
- API pages for operator[], at, front, back, find, contains, count, begin, end, cbegin, cend, items, and type_name of basic_json_view, linked both ways with the basic_json pages - the feature page and size() describe document order and duplicate keys - the examples show when the view helps: reading a few fields of a large text, probing optional members, and members in source order Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2.0 KiB
nlohmann::basic_json_view::find
iterator find(string_view_t key) const;
iterator find(const char* key) const;
iterator find(const string_t& key) const;
Finds a member with key key -- the first one, should the key occur more than once (see
Notes on duplicate keys). If the value is not an object, or no member has this key,
end() is returned.
Parameters
key(in)- key value of the element to search for
Return value
An iterator to the member with key key, or end() if there is none or the value is not an object.
Exception safety
No-throw guarantee: this function never throws exceptions.
Complexity
Linear in the number of members: as for ordered_json, members are compared one after
another, in document order, stopping at the first match. Each comparison first checks the key's length -- already
known from the index, without reading the key bytes -- before comparing its content.
Notes
Unlike BasicJsonType::find, which always returns #!cpp end() for a non-object type, this
also does so for a discarded view -- there is no separate "invalid" iterator to return.
Examples
??? example
The example below scans a batch of events for those that carry an optional `user_id` field, using `find()`
instead of [`operator[]`](operator[].md) (which would throw for the events that are not objects at all) or
[`contains()`](contains.md) followed by a second lookup. Events without a match are never materialized.
```cpp
--8<-- "examples/basic_json_view__find.cpp"
```
Output:
```json
--8<-- "examples/basic_json_view__find.output"
```
See also
- count - returns the number of occurrences of a key
- contains - checks whether a key exists
BasicJsonType::find- the corresponding function ofbasic_json
Version history
- Added in version 3.13.0.