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>
2.3 KiB
nlohmann::basic_json_view::begin
iterator begin() const noexcept;
Returns an iterator to the first element of an array, or the first member value of an object, in document order
— the order the values appear in the source text, not sorted by key. A primitive value iterates as a range of one
element (itself), and a #!json null value or a discarded view iterates as an empty range.
Return value
Iterator to the first element.
Exception safety
No-throw guarantee: this function never throws exceptions.
Complexity
Constant.
Notes
For an object, iteration visits every member, including all occurrences of a duplicate key — unlike
operator[], at, find, and contains,
which all resolve to the first member with a given key. See the
Notes on duplicate keys of operator[].
Because objects are iterated in document order rather than sorted by key, the order seen here can differ from what
iterating the materialize()d BasicJsonType value would produce: a #!cpp basic_json object
(std::map-backed by default) sorts its keys, while a view does not.
An ordered_json value also keeps document order, but it keeps only one entry per key: as parse() does, it keeps the
last value, at the position of the key's first occurrence. The view, in contrast, visits every member, including
the duplicates.
Examples
??? example
The example below iterates a log record's members with `begin()`/[`end()`](end.md) and prints them in the order
they were written. Materializing the record into a `BasicJsonType` object and iterating that would instead print
the members sorted by key.
```cpp
--8<-- "examples/basic_json_view__begin.cpp"
```
Output:
```json
--8<-- "examples/basic_json_view__begin.output"
```
See also
end- returns an iterator to one past the last elementcbegin- returns a const iterator to the first elementitems- access iterator member functions in range-based forBasicJsonType::begin- the corresponding function ofbasic_json
Version history
- Added in version 3.13.0.