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* Review and extend the documentation, and check it in CI A review of all documentation pages found factual errors, dead links, missing cross-references, and gaps in examples. This fixes them and adds checks so the same problems are caught automatically. Fixes: - wrong signatures and version histories (operator!= C++20 member, binary() subtype type, get<PointerType>(), JSON_NO_THREAD_LOCAL, ...) - stale descriptions (number parsing since #5283, UBJSON table, SAX example that no longer compiled, tsl::ordered_map advice) - dead internal and external links; repology.org badges (the domain is suspended) replaced by badges that query the registries directly - deprecation notes link the migration guide; the guide itself fixed Additions: - "See also" sections, cross-references, 25 runnable examples, 12 Mermaid diagrams, new API pages for json_pointer::operator<=> and byte_container_with_subtype::operator==/!= - landing page, guides for untrusted input and performance - "unreleased" badge after versions newer than the latest release Checks: - strict documentation build (broken links/anchors fail it); CI and the publish workflow fetch the full history the build needs - weekly external link check, Mermaid syntax check in CI - check_structure.py: example titles, heading levels, alt texts, header links, docset index coverage; its unused-example check works again - all examples produce the same output on every platform Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Keep the customer links that could not be fixed A dead link on the customers page is still the evidence of where the use of the library was documented. Keep the original URLs of the entries without a working replacement (Marne, Cisco Webex Desk Camera, Philips Hue, CyberArk) and exclude exactly these URLs from the link check. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct the duplicate-key recipe's claim about SAX positions The SAX interface's key() receives no position either; only parse_error() does. Also note that the recipe does not report the path to the repeated key (see discussion #5085). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Say the library is available as a single header and mention json_fwd.hpp Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct documentation errors found while hunting for bugs - patch/patch_inplace: list the JSON pointer errors parse_error.106-109 and out_of_range.402/404, and quote the actual parse_error.105 message. - unflatten: list parse_error.106/107/108 and out_of_range.404. - to_bson: list out_of_range.415 (binary subtype above 255) and note that 412 and 415 are new in 3.13.0. - to_string: state that string_t must be convertible to std::string, also in the StringType requirements table. - JSON Lines: a `while (input >> j)` loop also throws after the last value for concatenated JSON values; show a loop that works for both. - BON8: a string gets 0xFF only if nothing follows it in the message; a string at the end of an array or object is ended by 0xFE. - custom_string_type.hpp: add operator+=(char), which the "Always required" list asks for (json_pointer::to_string, flatten, unflatten, and diff did not compile), and an ADL int_to_string for diff and items. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Cache the release headers with functools.lru_cache Codacy (Pylint) flagged the mutable default argument that header() used as its cache. functools.lru_cache keeps the same memoization without it. The script's output is unchanged. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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3.1 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]
```
!!! 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 value
- type_name return the type as string
- operator value_t return the type of the JSON value
- is_primitive return whether the type is primitive
- is_structured return whether the type is structured
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.