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Niels Lohmann 52b72b5684 Improve documentation: byte layouts, release pages, See also, dark-mode images (#5906 )

- Make the iterator range illustrations legible in dark mode (prefers-color-scheme
  rules inside the SVGs).
- Add a "Byte layout" section with a color-coded byte table to each binary format
  page (BJData, BON8, BSON, CBOR, MessagePack, UBJSON), and highlight the smallest
  size per file in the comparison table.
- Add "See also" sections to the overview pages that lacked one.
- Split the release notes into one page per release, grouped by minor version on
  the overview page, with an "API changes" section per release generated from the
  API pages' version histories (hooks/api_changes.py).
- Fact-check the release notes and version histories against the release tags and
  correct wrong or misleading entries (e.g., json_serializer 2.1.0, merge_patch
  3.1.0, items, count, operator[], to_bjdata, std::string_view key support).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-10-24 17:57:44 +02:00

2.5 KiB

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nlohmann::basic_json::get_to

template<typename ValueType>
ValueType& get_to(ValueType& v) const noexcept(
    noexcept(JSONSerializer<ValueType>::from_json(
        std::declval<const basic_json_t&>(), v)));

Explicit type conversion between the JSON value and a compatible value. The value is filled into the input parameter by calling the json_serializer<ValueType> from_json() method.

The function is equivalent to executing

ValueType v;
JSONSerializer<ValueType>::from_json(*this, v);

This overload is chosen if:

ValueType is not basic_json,
json_serializer<ValueType> has a from_json() method of the form void from_json(const basic_json&, ValueType&)

v must not be const. Passing a const object is a compile-time error. For types such as arithmetic types, enums, and C arrays, the error is a static_assert that names the problem. For other types, the overload is not viable, and the compiler reports that no matching get_to was found.

Template parameters

ValueType: the value type to return

Return value

the input parameter, allowing chaining calls

Exception safety

Depends on what json_serializer<ValueType> from_json() method throws; the JSON value itself is never modified, since get_to() is a #!cpp const member function.

Exceptions

Depends on what json_serializer<ValueType> from_json() method throws

Complexity

Depends on the json_serializer<ValueType>::from_json() implementation.

Examples

??? example

The example below shows several conversions from JSON values to other types. There a few things to note: (1)
Floating-point numbers can be converted to integers, (2) A JSON array can be converted to a standard
`#!cpp std::vector<short>`, (3) A JSON object can be converted to C++ associative containers such as
`#!cpp std::map<std::string, json>`.
    
```cpp
--8<-- "examples/get_to.cpp"
```

Output:

```json
--8<-- "examples/get_to.output"
```

Version history

Added in version 3.3.0.
Added a static_assert with a clear message for const arguments in version 3.13.0.

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