json/docs/mkdocs/docs/api/json_sax/next_token_start.md

nlohmann::json_sax::next_token_start

Informs the sax parser about the start of the next element. There are two possible signatures for this method:

void next_token_start(std::size_t pos);

This version is called with the byte position where the next element starts. This version also works when parsing binary formats such as msgpack.

void next_token_start(const nlohmann::position_t&  p)

This version is called with detailed parser position information. This version only available when calling nlohmann::json::sax_parse with nlohmann::json::input_format_t::json and takes precedence.

Parameters

pos (in)

Byte position where the next element starts.

p (in)

Detailed parser position information after the first char of the next element was parsed.

Notes

Implementing either version is optional, and no function is called if neither version of next_token_start is available in the sax parser.

It is recommended, but not required, to also implement next_token_end.

Examples

??? example

The example below shows a SAX parser using the first version of this method to log the location.

```cpp
--8<-- "examples/sax_parse_with_src_location.cpp"
```

Output:

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

??? example

The example below shows a SAX parser using the second version of this method and
storing the location information in each json node using a [base class](../basic_json/json_base_class_t.md) for `nlohmann::json` as customization point.

```cpp
--8<-- "examples/sax_parse_with_src_location_in_json.cpp"
```

Output:

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

Version history

• Added in version ???.???.???.