mirror of
https://github.com/nlohmann/json.git
synced 2026-10-13 10:14:53 +00:00
Niels Lohmann
5bc36a6947
Add json_document and json_view, a read-only, zero-copy index of a JSON text, as the first public slice of the zero-copy view (#5295). A parse produces a flat array of 16-byte nodes in document order, one per value and one per object key. Strings stay in the source text; escaped strings are decoded into an arena. Integers are converted while their digits are in the cache; floats keep only their digit layout and are converted on read. Containers store the size of their subtree, so a reader can step over one in constant time. A document makes a handful of allocations, however many values it has. The parser accepts exactly what json::parse accepts, with every combination of ignore_comments and ignore_trailing_commas, with and without a trailing NUL, and under JSON_STRICT_NUL_HANDLING. It is portable C++11 and does not depend on byte order. basic_json_document adds parse, parse_copy, accept, read (reuses a document's memory), root, is_discarded, source, owns_source, node_count, memory_usage, and shrink_to_fit. basic_json_view adds type, the is_* queries, operator bool, size, empty, materialize, and source_offset. A parse error throws the same exception basic_json::parse would throw for the same input, message and position included. detail::abi_config keeps JSON_STRICT_NUL_HANDLING and JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON readable after json.hpp undefines them, in the ABI namespace so they always match the basic_json in use. A NUL byte that ends a // comment is the end of the input, as in parse() since #5696. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
35 lines
732 B
Markdown
35 lines
732 B
Markdown
# <small>nlohmann::</small>json_view
|
|
|
|
<small>Defined in header `<nlohmann/json_view.hpp>`</small>
|
|
|
|
```cpp
|
|
using json_view = basic_json_view<json>;
|
|
```
|
|
|
|
This type is a [`basic_json_view`](basic_json_view/index.md) of a value of a [`json_document`](json_document.md).
|
|
|
|
## Examples
|
|
|
|
??? example
|
|
|
|
The example below demonstrates how to use the type `nlohmann::json_view`.
|
|
|
|
```cpp
|
|
--8<-- "examples/json_view.cpp"
|
|
```
|
|
|
|
Output:
|
|
|
|
```json
|
|
--8<-- "examples/json_view.output"
|
|
```
|
|
|
|
## See also
|
|
|
|
- [json_document](json_document.md) - the document type this view refers into
|
|
- [ordered_json_view](ordered_json_view.md) - the corresponding view for `ordered_json_document`
|
|
|
|
## Version history
|
|
|
|
Since version 3.13.0.
|