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nlohmann
136 lines
4.2 KiB
Markdown
136 lines
4.2 KiB
Markdown
# <small>nlohmann::basic_json::</small>sax_parse
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```cpp
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// (1)
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template <typename InputType, typename SAX>
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static bool sax_parse(InputType&& i,
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SAX* sax,
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input_format_t format = input_format_t::json,
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const bool strict = true,
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const bool ignore_comments = false,
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const bool ignore_trailing_commas = false);
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// (2)
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template<class IteratorType, class SAX>
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static bool sax_parse(IteratorType first, IteratorType last,
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SAX* sax,
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input_format_t format = input_format_t::json,
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const bool strict = true,
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const bool ignore_comments = false,
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const bool ignore_trailing_commas = false);
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```
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Read from input and generate SAX events
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1. Read from a compatible input.
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2. Read from a pair of character iterators
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The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted
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respectively as UTF-8, UTF-16, and UTF-32.
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The SAX event lister must follow the interface of [`json_sax`](../json_sax/index.md).
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## Template parameters
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`InputType`
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: A compatible input, for instance:
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- an `std::istream` object
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- a `FILE` pointer
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- a C-style array of characters
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- a pointer to a null-terminated string of single byte characters
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- an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of
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iterators.
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`IteratorType`
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: a compatible iterator type for overload (2); a pair of character iterators whose `value_type` is an integral type
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with a size of 1, 2, or 4 bytes (interpreted respectively as UTF-8, UTF-16, and UTF-32)
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`SAX`
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: a class fulfilling the SAX event listener interface; see [`json_sax`](../json_sax/index.md)
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## Parameters
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`i` (in)
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: Input to parse from
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`sax` (in)
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: SAX event listener (must not be null)
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`format` (in)
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: the format to parse (JSON, CBOR, MessagePack, or UBJSON) (optional, `input_format_t::json` by default), see
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[`input_format_t`](input_format_t.md) for more information
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`strict` (in)
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: whether the input has to be consumed completely (optional, `#!cpp true` by default)
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`ignore_comments` (in)
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: whether comments should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error
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(`#!cpp false`); (optional, `#!cpp false` by default)
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`ignore_trailing_commas` (in)
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: whether trailing commas in arrays or objects should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error
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(`#!cpp false`); (optional, `#!cpp false` by default)
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`first` (in)
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: iterator to the start of a character range
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`last` (in)
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: iterator to the end of a character range
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## Return value
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return value of the last processed SAX event
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## Exception safety
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Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
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## Exceptions
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- Throws [`parse_error.101`](../../home/exceptions.md#jsonexceptionparse_error101) in case of an unexpected token, or
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empty input like a null `FILE*` or `char*` pointer.
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## Complexity
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Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the SAX
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consumer `sax` has a super-linear complexity.
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## Notes
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A UTF-8 byte order mark is silently ignored.
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## Examples
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??? example
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The example below demonstrates the `sax_parse()` function reading from string and processing the events with a
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user-defined SAX event consumer.
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```cpp
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--8<-- "examples/sax_parse.cpp"
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```
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Output:
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```json
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--8<-- "examples/sax_parse.output"
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```
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## See also
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- [parse](parse.md) - deserialize from a compatible input
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- [accept](accept.md) - check if the input is valid JSON
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## Version history
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- Added in version 3.2.0.
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- Ignoring comments via `ignore_comments` added in version 3.9.0.
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- Added `ignore_trailing_commas` in version 3.12.x.
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!!! warning "Deprecation"
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Overload (2) replaces calls to `sax_parse` with a pair of iterators as their first parameter which has been
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deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like
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`#!cpp sax_parse({ptr, ptr+len});` with `#!cpp sax_parse(ptr, ptr+len);`.
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