# <small>nlohmann::</small>json_sax

```cpp
template<typename BasicJsonType>
struct json_sax;
```

This class describes the SAX interface used by [sax_parse](../basic_json/sax_parse.md). Each function is called in
different situations while the input is parsed. The boolean return value informs the parser whether to continue
processing the input.

For instance, parsing the JSON text `{"a": [1, true]}` triggers the following callbacks, in order:

```mermaid
sequenceDiagram
    participant P as Parser
    participant H as SAX handler

    P->>H: start_object(elements)
    P->>H: key("a")
    P->>H: start_array(elements)
    P->>H: number_unsigned(1)
    P->>H: boolean(true)
    P->>H: end_array()
    P->>H: end_object()
```

Note `elements` is passed as `#!cpp std::numeric_limits<std::size_t>::max()` (i.e., "unknown") for JSON text input;
only binary formats such as CBOR or MessagePack may report the actual number of elements in `start_object`/
`start_array`. Also note that `1` is reported via `number_unsigned` rather than `number_integer` because it has no
leading `-` sign.

## Template parameters

`BasicJsonType`
:   a specialization of [`basic_json`](../basic_json/index.md)

## Member types

- [**number_integer_t**](../basic_json/number_integer_t.md) - `BasicJsonType`'s type for numbers (integer)
- [**number_unsigned_t**](../basic_json/number_unsigned_t.md) - `BasicJsonType`'s type for numbers (unsigned)
- [**number_float_t**](../basic_json/number_float_t.md) - `BasicJsonType`'s type for numbers (floating-point)
- [**string_t**](../basic_json/string_t.md) - `BasicJsonType`'s type for strings
- [**binary_t**](../basic_json/binary_t.md) - `BasicJsonType`'s type for binary arrays

## Member functions

- [**binary**](binary.md) (_virtual_) - a binary value was read
- [**boolean**](boolean.md) (_virtual_) - a boolean value was read
- [**end_array**](end_array.md) (_virtual_) - the end of an array was read
- [**end_object**](end_object.md) (_virtual_) - the end of an object was read
- [**key**](key.md) (_virtual_) - an object key was read
- [**null**](null.md) (_virtual_) - a null value was read
- [**number_float**](number_float.md) (_virtual_) - a floating-point number was read
- [**number_integer**](number_integer.md) (_virtual_) - an integer number was read
- [**number_unsigned**](number_unsigned.md) (_virtual_) - an unsigned integer number was read
- [**parse_error**](parse_error.md) (_virtual_) - a parse error occurred
- [**start_array**](start_array.md) (_virtual_) - the beginning of an array was read
- [**start_object**](start_object.md) (_virtual_) - the beginning of an object was read
- [**string**](string.md) (_virtual_) - a string value was read

## Version history

- Added in version 3.2.0.
- Support for binary values (`binary_t`, `binary`) added in version 3.8.0.