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Niels Lohmann
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* 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>
3.4 KiB
3.4 KiB
nlohmann::basic_json::value_t
enum class value_t : std::uint8_t {
null,
object,
array,
string,
boolean,
number_integer,
number_unsigned,
number_float,
binary,
discarded
};
This enumeration collects the different JSON types. It is internally used to distinguish the stored values, and the
functions is_null, is_object, is_array, is_string,
is_boolean, is_number (with is_number_integer,
is_number_unsigned, and is_number_float),
is_discarded, is_binary, is_primitive, and
is_structured rely on it.
Notes
!!! note "Ordering"
The order of types is as follows:
1. `null`
2. `boolean`
3. `number_integer`, `number_unsigned`, `number_float`
4. `object`
5. `array`
6. `string`
7. `binary`
`discarded` is unordered.
```mermaid
flowchart LR
A[null] --> B[boolean]
B --> C["number_integer / number_unsigned / number_float"]
C --> D[object]
D --> E[array]
E --> F[string]
F --> G[binary]
```
<p class="nj-caption" markdown>Arrows point from a type to the next greater type in the ordering used by
`operator<`.</p>
!!! note "Types of numbers"
There are three enumerators for numbers (`number_integer`, `number_unsigned`, and `number_float`) to distinguish
between different types of numbers:
- [`number_unsigned_t`](number_unsigned_t.md) for unsigned integers
- [`number_integer_t`](number_integer_t.md) for signed integers
- [`number_float_t`](number_float_t.md) for floating-point numbers or to approximate integers which do not fit
into the limits of their respective type
!!! warning "Comparison operators"
`operator<` and `operator<=>` (since C++20) are overloaded and compare according to the ordering described above.
Until C++20 all other relational and equality operators yield results according to the integer value of each
enumerator. Since C++20 some compilers consider the _rewritten candidates_ generated from `operator<=>` during
overload resolution, while others do not. For predictable and portable behavior use:
- `operator<` or `operator<=>` when wanting to compare according to the order described above
- `operator==` or `operator!=` when wanting to compare according to each enumerators integer value
Examples
??? example
The following code how `type()` queries the `value_t` for all JSON types.
```cpp
--8<-- "examples/type.cpp"
```
Output:
```json
--8<-- "examples/type.output"
```
See also
type- return the type of the JSON valuetype_name- return the type as stringoperator value_t- return the type of the JSON valueis_primitive- return whether the type is primitiveis_structured- return whether the type is structured- Types - the JSON value types and how they are stored
Version history
- Added in version 1.0.0.
- Added unsigned integer type in version 2.0.0.
- Added binary type in version 3.8.0.