Niels Lohmann
a47170346a
* docs: new design for the documentation site Apply the brand to the Material for MkDocs site: Inter and JetBrains Mono served by the site (upright and real italic), brand colours, blue header band with the syntax pattern, wordmark in the header, new home page (hero, cards, animated feature tour), 404 page, polish for tabs, search, footer, focus rings, tables and code blocks, and theme features (code copy, previous/next footer, TOC follow, search suggestions). Draw the number railroad diagram, the parser callback events and the iterator illustrations as inline SVGs that follow the light and dark scheme. The generator scripts are in docs/mkdocs/scripts/figures; the feature slideshow (json-light.svg, json-dark.svg, replacing json.gif on the home page) is built by docs/mkdocs/scripts/slideshow. Decision nodes in five flowcharts become hexagons, which need far less room. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: add figures, table captions and a macro chooser - Figures with numbered captions: SAX stepper, json_view layout and edit stepper, exception map, JSON pointer and patch walkers, QA pipeline, scaling and binary size charts, roadmap lanes, release timeline, integration decision tree and namespace builder - Table captions (nj-table-caption) on 9 pages - Compile times: modules and PCH charts, filesystem section, re-measured Figure 1, links between features/modules.md and compile_times.md - Interactive macro chooser for features/arbitrary_types.md - Link check: exclude URLs that answer the plugin with 400/401/419 or are dead (customers.md) Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: macro chooser generates adl_serializer for non-default-constructible types Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: cross-link concept pages and API pages in See also sections 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> * docs: address review comments on the new design - Home: add a "Latest release" button - Sponsors: update the list and group it by tier - Features: list all feature pages on the index page - Releases: add highlights per release, link the 4.0 roadmap, add the first commit to the timeline - Exceptions: prefix all example messages with the exception name - API: no code font for format names in the See also links of the to_/from_ pages - Merge Patch: show the document before, the patch, and the result - Replace "--" with typographic dashes, mark external links with an icon, center Mermaid diagrams Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2.4 KiB
nlohmann::basic_json_view::count
size_type count(string_view_t key) const;
size_type count(const char* key) const;
size_type count(const string_t& key) const;
Returns the number of members with key key if the value is an object, #!cpp 0 otherwise. Members with a repeated
key are all counted.
Parameters
key(in)- key value of the element to count
Return value
the number of members of the object with key key (duplicates included), or #!cpp 0 if the value is not an object
or has no such member.
Exception safety
No-throw guarantee: this function never throws exceptions.
Complexity
Linear in the number of members: unlike the lookup functions, count() does not stop at the first match, because it
has to count every member with the key. Members are compared one after another, in document order. Each comparison
first checks the key's length — already known from the index, without reading the key bytes — before comparing its
content. The hash index of the keys of objects with 128 or more members does not help here, since every member
is visited.
Notes
This method always returns #!cpp 0 when the value is not an object — including a discarded
view.
If the source text repeats a key, count() returns more than #!cpp 1 for it, even though the
materialized value (like the result of parse()) would have only one member with that key. Hence
#!cpp count(key) > 1 detects duplicate keys. This is unlike the lookup functions
(operator[], at, find, contains), which resolve to the
first member; see the Notes on duplicate keys of operator[].
Examples
??? example
The example below validates that every transaction of a batch carries exactly one `amount` field, using
`count()` before deciding whether to materialize a transaction at all. It reports a transaction with no `amount`
field and one with a duplicated `amount` field.
```cpp
--8<-- "examples/basic_json_view__count.cpp"
```
Output:
```json
--8<-- "examples/basic_json_view__count.output"
```
See also
find- find a value in an objectcontains- checks whether a key existsBasicJsonType::count- the corresponding function ofbasic_json
Version history
- Added in version 3.13.0.