Niels Lohmann
8a0679558f
- Copying is disabled because of its cost, not because of two documents borrowing the same buffer; the unique_ptr follows from move-only. - Inputs: streams, FILE*, and wide characters (strings, arrays, pointers) are all supported and owned; point to parse_copy() for owned copies. - The error replay only runs for failing input, builds no values, and is skipped with allow_exceptions = false. - read() writes copied inputs into the previous owned copy. - Views can dangle like std::string_view, and why there is no shared/weak pointer design. - The 4 GiB limit (16-byte nodes, 16-byte scanner steps), streams being read to the end first, which macros apply, why materialize() has no source positions, and wording nits (accept() vs basic_json::accept(), is_binary, is_discarded, see-also lists, size table, "back into"). Signed-off-by: Niels Lohmann <mail@nlohmann.me>
3.0 KiB
nlohmann::basic_json_document
Defined in header <nlohmann/json_view.hpp>
template<typename BasicJsonType>
class basic_json_document;
A parsed JSON text, held as a flat index of its values
(16 bytes per value) instead of a tree of BasicJsonType values.
Strings and numbers stay in the source text; only strings that contain escapes are decoded, into one buffer owned by
the document. basic_json_view is a read-only handle to one value of a
basic_json_document; materialize() turns a subtree into the
BasicJsonType value that BasicJsonType::parse() would have produced for it.
A document may borrow the text it was parsed from (the caller's buffer must then outlive the document) or own
it (a copy, or an rvalue #!cpp std::string that was moved in); see owns_source. basic_json_document
is move-only: a copy would duplicate the whole index, the decoded-string buffer, and the owned text, and a move is
enough in every use we know of. The index, the decoded strings, and the owned text live in one heap block that the
document holds through a #!cpp std::unique_ptr; this is also why views survive a move of the document.
Template parameters
BasicJsonType- a specialization of
basic_json, for instancejsonorordered_json. Only 64-bitnumber_integer_t/number_unsigned_ttypes are supported; this is checked with astatic_assert.
Specializations
- json_document - documents of the default specialization
json - ordered_json_document - documents of
ordered_json
Member types
- view_type - the type of view returned by
root()(#!cpp basic_json_view<BasicJsonType>) - value_t - the JSON type enumeration, see
basic_json::value_t
Member functions
- (constructor)
- parse (static) - deserialize from a compatible input, borrowing or owning it as appropriate
- parse_copy (static) - deserialize a copy of a compatible input
- accept (static) - check whether the input is valid JSON
- read - (re-)parse into this document, reusing its memory
- root - the view of the root value
- is_discarded - return whether the last parse failed
- source - the parsed text
- owns_source - return whether the document holds its own copy of the text
- node_count - the number of index entries (values plus object keys)
- memory_usage - the number of bytes held by the document
- shrink_to_fit - release unused index capacity
Version history
- Added in version 3.13.0.