mirror of
https://github.com/nlohmann/json.git
synced 2026-10-27 16:28:57 +00:00
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>
1.5 KiB
1.5 KiB
nlohmann::basic_json::front
reference front();
const_reference front() const;
Returns a reference to the first element in the container. For a JSON container #!cpp c, the expression
#!cpp c.front() is equivalent to #!cpp *c.begin().
Return value
In the case of a structured type (array or object), a reference to the first element is returned. In the case of number, string, boolean, or binary values, a reference to the value is returned.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
Exceptions
If the JSON value is #!json null, exception
invalid_iterator.214 is thrown.
Complexity
Constant.
Notes
!!! info "Precondition"
The array or object must not be empty. Calling `front` on an empty array or object yields undefined behavior.
Examples
??? example
The following code shows an example for `front()`.
```cpp
--8<-- "examples/front.cpp"
```
Output:
```json
--8<-- "examples/front.output"
```
See also
back- to access the last elementbasic_json_view::front- the same access on a zero-copy view (document order, not sorted; duplicate keys are visited)- Element Access - overview of all ways to access elements
Version history
- Added in version 1.0.0.
- Binary values are supported since version 3.8.0.