mirror of
https://github.com/nlohmann/json.git
synced 2026-11-06 20:49:21 +00:00
Niels Lohmann
933952e095
The parser and the lexer exchange one token at a time, and the lexer keeps its state (the current character, a pending unget, where the token starts) in members, which every character pays for: json::accept() of twitter.json took 2.8x as long as json_document::accept(). detail::contiguous_parser reads text in one block of memory through a local pointer, with the grammar, the whitespace and the tokens in one loop (after yyjson's reader), and drives a SAX handler: parse()'s DOM handler, accept()'s handler, or the user's handler of sax_parse(). It is used with the default options (no callback, no comments, no trailing commas; sax_parse() with strict = true). Errors are reported by the library parser, so the exception, its message and its position stay the same. contiguous_parser stops at the token that the library parser would reject, before reporting it, so the events up to the error are the same; then: - parse() runs the library parser with a handler that only reports the error (json_sax_error_reporter), with the lexer of parse(), which is instantiated anyway; - sax_parse() runs it with a handler that forwards only parse_error() to the user's handler (json_sax_error_forwarder), so no event arrives twice; - accept() returns the verdict. A handler that returns false stops the parse as before. An error at the end of a large input costs parse() about 1.2x of what it cost before. On an Apple M1 Max: accept() 1.6-2.0x as fast, parse() 10-16% faster, ordered_json 11-16%, sax_parse() with a user's handler 1.36-1.46x, small messages 12-22% (parse()) and 2.1-2.4x (accept()). On x86-64 (GCC 15, Clang 21): accept() 1.6-1.9x, parse() 5-17%, ordered_json 12-19%, sax_parse() 1.32-1.57x. A translation unit that parses a string compiles 3% (-O0) and 9% (-O2) slower. unit-contiguous_parser.cpp compares the contiguous path with the byte path (std::list iterators) on corner cases, generated documents, their truncations and mutations, deep nesting, and narrow number types: the same values with the same number types and float bits, exception messages, accept() verdicts and sax_parse() events. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Documentation
Generate documentation
Note on documentation: The source files contain links to the online documentation at https://json.nlohmann.me.
This URL provides the most recent documentation and also applies to previous versions. Documentation for deprecated
functions is not removed; instead, it is marked as deprecated.
If you want to view the documentation for a specific tag or commit hash, you can generate it locally as follows (example
using tag v3.12.0):
git clone https://github.com/nlohmann/json.git
cd json
git checkout v3.12.0
make install_venv serve -C docs/mkdocs
Open http://127.0.0.1:8000/ in your browser. Replace any URL in the source code that points to
https://json.nlohmann.me with http://127.0.0.1:8000 to view the documentation for the selected tag or commit hash.