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Add json_document and json_view: node index, parser, and document

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Add json_document and json_view, a read-only, zero-copy index of a
JSON text, as the first public slice of the zero-copy view (#5295).

A parse produces a flat array of 16-byte nodes in document order,
one per value and one per object key. Strings stay in the source
text; escaped strings are decoded into an arena. Integers are
converted while their digits are in the cache; floats keep only
their digit layout and are converted on read. Containers store the
size of their subtree, so a reader can step over one in constant
time. A document makes a handful of allocations, however many
values it has.

The parser accepts exactly what json::parse accepts, with every
combination of ignore_comments and ignore_trailing_commas, with and
without a trailing NUL, and under JSON_STRICT_NUL_HANDLING. It is
portable C++11 and does not depend on byte order.

basic_json_document adds parse, parse_copy, accept, read (reuses a
document's memory), root, is_discarded, source, owns_source,
node_count, memory_usage, and shrink_to_fit. basic_json_view adds
type, the is_* queries, operator bool, size, empty, materialize,
and source_offset. A parse error throws the same exception
basic_json::parse would throw for the same input, message and
position included.

detail::abi_config keeps JSON_STRICT_NUL_HANDLING and
JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON readable after json.hpp
undefines them, in the ABI namespace so they always match the
basic_json in use.

A NUL byte that ends a // comment is the end of the input, as in
parse() since #5696.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-07 16:42:22 +02:00
1 parent bfa4886f0f
commit 759dd2e1b1
146 files changed
+9611 -13
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tests/benchmarks/src/benchmarks.cpp
+25
View File
@@ -81,6 +81,31 @@ BENCHMARK_CAPTURE(ParseString, signed_ints, TEST_DATA_DIRECTORY "/regressi
BENCHMARK_CAPTURE(ParseString, unsigned_ints, TEST_DATA_DIRECTORY "/regression/unsigned_ints.json");
BENCHMARK_CAPTURE(ParseString, small_signed_ints, TEST_DATA_DIRECTORY "/regression/small_signed_ints.json");
//////////////////////////////////////////////////////////////////////////////
// validate JSON from string
//////////////////////////////////////////////////////////////////////////////
static void Accept(benchmark::State& state, const char* filename)
{
std::ifstream f(filename);
std::string str((std::istreambuf_iterator<char>(f)), std::istreambuf_iterator<char>());
while (state.KeepRunning())
{
benchmark::DoNotOptimize(json::accept(str));
}
state.SetBytesProcessed(state.iterations() * str.size());
}
BENCHMARK_CAPTURE(Accept, jeopardy, TEST_DATA_DIRECTORY "/jeopardy/jeopardy.json");
BENCHMARK_CAPTURE(Accept, canada, TEST_DATA_DIRECTORY "/nativejson-benchmark/canada.json");
BENCHMARK_CAPTURE(Accept, citm_catalog, TEST_DATA_DIRECTORY "/nativejson-benchmark/citm_catalog.json");
BENCHMARK_CAPTURE(Accept, twitter, TEST_DATA_DIRECTORY "/nativejson-benchmark/twitter.json");
BENCHMARK_CAPTURE(Accept, floats, TEST_DATA_DIRECTORY "/regression/floats.json");
BENCHMARK_CAPTURE(Accept, signed_ints, TEST_DATA_DIRECTORY "/regression/signed_ints.json");
BENCHMARK_CAPTURE(Accept, unsigned_ints, TEST_DATA_DIRECTORY "/regression/unsigned_ints.json");
BENCHMARK_CAPTURE(Accept, small_signed_ints, TEST_DATA_DIRECTORY "/regression/small_signed_ints.json");
//////////////////////////////////////////////////////////////////////////////
// parse pretty-printed JSON from string
//