Niels Lohmann
444dba381f
- Figures with numbered captions: SAX stepper, json_view layout and edit stepper, exception map, JSON pointer and patch walkers, QA pipeline, scaling and binary size charts, roadmap lanes, release timeline, integration decision tree and namespace builder - Table captions (nj-table-caption) on 9 pages - Compile times: modules and PCH charts, filesystem section, re-measured Figure 1, links between features/modules.md and compile_times.md - Interactive macro chooser for features/arbitrary_types.md - Link check: exclude URLs that answer the plugin with 400/401/419 or are dead (customers.md) Signed-off-by: Niels Lohmann <mail@nlohmann.me>
3.3 KiB
nlohmann::json_sax
template<typename BasicJsonType>
struct json_sax;
This class describes the SAX interface used by sax_parse. 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:
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()
Each arrow is one call from the parser to the SAX handler, from top to bottom in the order the calls happen.
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
Member types
- number_integer_t -
BasicJsonType's type for numbers (integer) - number_unsigned_t -
BasicJsonType's type for numbers (unsigned) - number_float_t -
BasicJsonType's type for numbers (floating-point) - string_t -
BasicJsonType's type for strings - binary_t -
BasicJsonType's type for binary arrays
Member functions
- binary (virtual) - a binary value was read
- boolean (virtual) - a boolean value was read
- end_array (virtual) - the end of an array was read
- end_object (virtual) - the end of an object was read
- key (virtual) - an object key was read
- null (virtual) - a null value was read
- number_float (virtual) - a floating-point number was read
- number_integer (virtual) - an integer number was read
- number_unsigned (virtual) - an unsigned integer number was read
- parse_error (virtual) - a parse error occurred
- start_array (virtual) - the beginning of an array was read
- start_object (virtual) - the beginning of an object was read
- string (virtual) - a string value was read
See also
- SAX interface - guide to event-based parsing
- sax_parse - generate SAX events from an input
- parse - DOM parsing, with optional parser callbacks
- Parse exceptions
Version history
- Added in version 3.2.0.
- Support for binary values (
binary_t,binary) added in version 3.8.0.