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Niels Lohmann 253e4c3926 Bound what the DOM parsers reserve for arrays that announce a size (#6082) 
* Bound the total number of valueless UBJSON elements per input

An optimized UBJSON array of type Z, T or F has no payload, so its
declared count is not bounded by the input. The limit of 1048576 applied
to each array on its own, so 9 bytes (`[$Z#l` and a count) produced
1048576 values and every further 9 bytes another 1048576: 362 bytes
allocated 661 MB in a DOM, and a SAX handler received 1M events per 9
bytes.

The reader now adds the counts of all such arrays of one input and
rejects the input with out_of_range.408 when the sum exceeds 1048576
plus 4 for every byte read so far. The base is the per-array limit, so
an array that was accepted on its own before is still accepted at the
start of an input. These arrays add about 80 bytes of memory per input
byte (measured 77; one `Z` per byte needs 32), plus the base; the memory
of a document as a whole is not bounded by this. The check runs once per
valueless array, before its start event, with plain size_t arithmetic
that cannot overflow for a 32-bit size_t. Containers with a payload type
and objects (every member needs a key) are bounded by the input already
and are unchanged. BJData rejects these types.

to_ubjson counts the elements of the typed arrays it writes in one call
and writes an array in the unoptimized form (`[#n Z Z ...`) once it would
bring the total above 1048576, which a reader accepts at any input size.
The check is made only for a typed array of a valueless type, so BJData
and other arrays do not pay for it. Everything to_ubjson writes in
version 3.13.0 can therefore be read back.

Two consequences:
- to_ubjson output changes for values with more than 1048576 elements in
  arrays of type Z, T or F: such an array is written at one byte per
  element, e.g. 270000 rows of 100 nulls take 26.8 MB instead of 1.35 MB.
- Output of version 3.12.0 and earlier (typed arrays without such a
  total) is rejected by from_ubjson when the arrays hold more than
  1048576 elements plus 4 per byte of input. 3.12.0 writes a row of up to 255 nulls in 5 bytes (6 above
  255), so a table is rejected from 1075 rows of 1000 nulls or 209723
  rows of 25 (accepted: 1000 rows of 1000, 209000 rows of 25); rows of
  20 or fewer are never rejected.

Measured on the test data: no file of json_test_data (converted with
to_ubjson in all three modes, 846 round trips) holds an array of this
kind with more than 0.17 values per byte. All of them are read back.

Reproducer (K arrays of 1048576 nulls), Apple clang -O2:
  K=40 (362 bytes): before 41943040 values, 664 MB; after rejected, 33 MB
  K=2 (20 bytes):   before 2097152 values, 53 MB;   after rejected, 33 MB

The new tests count events with a SAX handler where they can: building
and comparing million-element values made the first version take 176 s
under Valgrind, the current one about 22 s.

Behaviour change: an input that holds more than 1048576 elements in
arrays of type Z, T or F at more than 4 per byte is now rejected.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Report an empty array for UBJSON `[$N#<n>` instead of n elements

A no-op (N) is not a value, so an optimized array of type N holds no
element whatever count it declares. The reader skipped the elements but
still passed the declared count to the SAX parser: a handler was told
start_array(n) and no element followed, and the DOM parser reserved
min(n, 16384) values (256 KB) for an array that stays empty. Nine bytes
(`[$N#l 0x7FFFFFFF`) therefore committed 256 KB: 2000 of them in one
input, 18 KB, committed 512 MB of heap (capacity 163,840,000 values for
the 10000 arrays of the original probe: 2.6 GB for 70 KB of input).
Untouched pages keep the resident size small, but the commit charge and
a 32-bit address space are consumed.

The reader now announces 0 elements for an optimized array of type N.
The loop that skips the elements is unchanged (it never ran). A count
that does not fit into std::size_t is still rejected by the count
reader; a count that is too large for the array type of the DOM (before:
out_of_range.408 "excessive array size" from the DOM handler) is
accepted now, because the array is empty.

Behaviour change: sax_parse reports start_array(0) for `[$N#n` (before:
n); from_ubjson no longer throws out_of_range.408 for an N-typed array
whose count exceeds the maximum size of the array type.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Bound what the DOM parsers reserve for arrays that announce a size

Cause: #5476 made the DOM parsers reserve storage (up to 16384 elements)
for a counted array of CBOR, MessagePack, UBJSON and BJData when it
opens, before any input backs the count. The arrays that are open at the
same time keep their storage until the parse ends, so N nested headers
that announce 16384 elements and are never completed hold
N * 16384 * sizeof(json): 100,000 nested CBOR headers `99 40 00`
(300,000 bytes) peaked at 1.65 GiB, 3.12.0 at 12 MiB; the same for
MessagePack `DC 40 00`, UBJSON `[#I 16384` and BJData.

Fix: json_sax_dom_error_state, the base of the three DOM parsers, keeps a
credit of elements that may still be reserved: 65,536 at the start plus
2 for every byte the reader has read. An array that announces no more
than the credit left is reserved as before (one comparison and one
subtraction per counted array); a larger one is reserved what is left
and grows as its elements arrive. binary_reader tells a DOM parser (a
handler whose pointer converts to json_sax_dom_error_state*; a handler
that derives from one privately or protectedly, or any other SAX handler,
is not told anything and reserves as in the base of this change) where to
find its count of characters read for the duration of sax_parse(). An
RAII guard puts back the previous binding on every exit, also by
exception, so the parser never keeps a pointer to a reader that is gone
(unbound, only the per-array cap of 16384 applies); the public SAX
interface is unchanged, and start_array() still reports the announced number. A
bound per array by the remaining input would not help, since the same
bytes would back every open level; the bound has to be over all arrays.

The elements of an array take at least one byte of input each, so the
credit is more than honest input needs: none of the 19 inputs measured
(canada, citm_catalog, twitter, mesh, update-center, random, numbers,
animation, ik_rig, instruments, geo_response, jeopardy and 7 synthetic
ones, each as CBOR, MessagePack, UBJSON and BJData, with and without
size/type optimization) was given less than it announced. A value that
nests five or more arrays of 16384 elements, each with an array as its
first element, is the exception: the later ones grow as before.

Measurements (clang -O2, macOS arm64, peak memory footprint of
`/usr/bin/time -l`, reproducer: n nested headers):

              n = 20,000                n = 100,000
              develop   fix   3.12.0   develop    fix   3.12.0
  CBOR        338.7    5.9    8.2      1687.7    23.3   11.8   MiB
  MessagePack 338.9    6.0    7.3      1687.9    23.8   11.9   MiB
  UBJSON      339.0    7.6    8.0      1687.9    30.1   11.6   MiB
  BJData      339.0    7.3    7.9      1688.0    30.8   11.6   MiB

That is at most (65,536 + 2 per input byte) values: 1 MiB plus 32 bytes
per input byte with 16-byte values (a value is 24 bytes with
JSON_DIAGNOSTICS and up to 40 with JSON_DIAGNOSTIC_POSITIONS), as
documented in untrusted_input.md. Lower fixed caps do not get there: a
cap of 64 elements still peaks at 113 MiB (n = 100,000) and costs 4.7 %
on arrays of 300 elements (mat300.cbor) and 5.0 % on arrays of 10,000
(arrays_of_big.cbor).

Reader instructions retired (min of 7, 108 rows: 18 inputs in the 6 forms
CBOR, MessagePack, UBJSON and BJData plain and optimized; jeopardy, 46 MB,
is within 0.1 %), compared with the base of this change: -0.19 % to +0.37 % in the formats that announce
sizes (canada.cbor 81.9 M -> 82.1 M, many_small.cbor 333.5 M -> 334.2 M);
the benefit of #5476 is kept (without any reserve canada.cbor takes
116.8 M, +42.6 %, many_small.cbor +71.5 %, mat300.cbor +81.6 %). Rows of
plain UBJSON and BJData, whose arrays announce no size, move by -2.7 % to
+2.6 % without any code of theirs changing: the base alternates
between two instruction counts per process (452 M and 463 M for
many_pairs.ubjson, equal in cycles), and a struct with three unused
members added to the same class reproduces the 474 M mode.

Tests (CBOR, MessagePack, UBJSON, BJData): 200 nested headers that
announce 16384 elements peak at 52,433,600 bytes of DOM allocations on
the base and below 128 Ki values with the fix (scaled by sizeof(value),
so that it holds with the diagnostic macros) (counting allocator, no
process memory measured); an array that completes is still reserved in
one allocation; CBOR also checks that a DOM parser is not bound to a finished
parse (ASan: stack-use-after-scope without the guard), that wrappers
derived publicly (also with a parse inside the parse), privately and
protectedly compile and are bound or not as described, that an array that got less than it
announced decodes and that a SAX handler is told the announced size.
The new tests take 4.6 s under Valgrind at -O0 (gcc:12, all four files).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Clarify the reservation note for announced array counts

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Report an empty array for UBJSON [$N#<n>] instead of n elements (#6079)

* Report an empty array for UBJSON `[$N#<n>` instead of n elements

A no-op (N) is not a value, so an optimized array of type N holds no
element whatever count it declares. The reader skipped the elements but
still passed the declared count to the SAX parser: a handler was told
start_array(n) and no element followed, and the DOM parser reserved
min(n, 16384) values (256 KB) for an array that stays empty. Nine bytes
(`[$N#l 0x7FFFFFFF`) therefore committed 256 KB: 2000 of them in one
input, 18 KB, committed 512 MB of heap (capacity 163,840,000 values for
the 10000 arrays of the original probe: 2.6 GB for 70 KB of input).
Untouched pages keep the resident size small, but the commit charge and
a 32-bit address space are consumed.

The reader now announces 0 elements for an optimized array of type N.
The loop that skips the elements is unchanged (it never ran). A count
that does not fit into std::size_t is still rejected by the count
reader; a count that is too large for the array type of the DOM (before:
out_of_range.408 "excessive array size" from the DOM handler) is
accepted now, because the array is empty.

Behaviour change: sax_parse reports start_array(0) for `[$N#n` (before:
n); from_ubjson no longer throws out_of_range.408 for an N-typed array
whose count exceeds the maximum size of the array type.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Clarify the reservation note for announced array counts

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Add JSON_UBJSON_VALUELESS_ELEMENTS_PER_BYTE to set the UBJSON whole-input budget (#6083)

* Add JSON_UBJSON_VALUELESS_ELEMENTS_PER_BYTE to set the UBJSON whole-input budget

The whole-input budget for the elements of optimized UBJSON arrays of
type Z, T and F (1048576 plus 4 per byte read) rejects files written by
3.12.0 that have long arrays of these types, such as 1100 rows of 1000
nulls with a `$Z` annotation, and there was no way to read them. The
per-byte rate is now the macro JSON_UBJSON_VALUELESS_ELEMENTS_PER_BYTE.

Semantics:
- default 4, so the default build is unchanged (the generated code of
  from_ubjson is identical at -O2 up to source line numbers);
- the value must be a positive integer: 0, negative, non-integral, bool,
  character and wider-than-uintmax_t values fail to compile with a
  static_assert that names the macro;
- a value that does not fit into std::size_t is the largest size_t, so
  one spelling works for 32- and 64-bit targets;
- the limit base + rate * bytes_read saturates at the largest size_t
  instead of wrapping around, for any rate and input size; a rate of
  131072 (2^20 / 8) or more cannot be exceeded by any input (the
  shortest header of an array of more than 32767 elements is 8 bytes),
  which switches the whole-input budget off;
- the limit of one array (1048576) and the base (1048576) stay fixed
  constants, so the writer fallback still follows the base only and a
  reader with any rate reads everything the writer produces;
- the macro is not part of the ABI tag and must have the same value in
  every translation unit; it is documented that way.

The memory the arrays can take in a DOM is about 20 bytes per rate and
byte of input (measured, macOS, containers of 9 * rate elements:
25 bytes per input byte at rate 1, 81 at 4, 312 at 16, 1226 at 64, 5493
at 256) plus about 33 MB for the base. A 3.12.0 row of N values has a
header of b bytes (5 up to 255, 6 up to 32767, 8 above), so a table is
read completely if N <= rate * b, and otherwise up to
(1048576 + h * rate, h = outer header: 6, 7 or 9 bytes) / (N - rate * b) rows; 1100 rows of 1000 nulls need
a rate of 8. The new page of the macro documents the formulas, the
measurements, and two examples that are run by the documentation checks.

The tests of the budget move to tests/src/unit-ubjson_valueless.cpp, which
derives every boundary from the macro and is built with the rates 1,
1000000 and 0xFFFFFFFFFFFFFFFF in addition to the default (the last two
check that nothing is refused and that the limit does not wrap around);
they fail with the unchanged header for rate 1, 1000000 and the maximum.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Refuse char8_t for JSON_UBJSON_VALUELESS_ELEMENTS_PER_BYTE and clarify its documentation

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Use fseek instead of rewind in the UBJSON FILE* test

clang-tidy (bugprone-unsafe-functions) rejects rewind() because it has no
error detection. Check the result of fseek() instead.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Charge an announced array only what is reserved for it

An array that announced more than reserve_cap() elements but no more than
the credit left was charged the announced count, while reserve_array()
reserved at most reserve_cap() of them. An outer array of 20000 elements
therefore left a third nested array of 16384 with 12796 instead of the
full reservation. reserve_count() now caps the count first and charges
that, and the DOM parsers reserve it through reserve_array_capped(),
which does not cap again, so the fast path costs the same as before
(instructions retired within +-0.06 % on canada, citm_catalog and twitter
in CBOR, MessagePack and UBJSON).

Also re-wrap the comment of valueless_elements_base.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-11-15 17:02:05 +01:00

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# Project information
site_name: JSON for Modern C++
site_description: JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type.
site_author: Niels Lohmann
site_url: https://json.nlohmann.me/
# Repository
repo_name: nlohmann/json
repo_url: https://github.com/nlohmann/json
edit_uri: edit/develop/docs/mkdocs/docs
# Copyright
copyright: Copyright &copy; 2013-2026 Niels Lohmann
# Configuration
theme:
name: material
custom_dir: overrides
language: en
palette:
- media: '(prefers-color-scheme: light)'
scheme: default
primary: custom
accent: custom
toggle:
icon: material/brightness-7
name: Switch to dark mode
- media: '(prefers-color-scheme: dark)'
scheme: slate
primary: custom
accent: custom
toggle:
icon: material/brightness-4
name: Switch to light mode
icon:
repo: fontawesome/brands/github
font: false
logo: images/wordmark-header.svg
features:
- navigation.instant
- navigation.tracking
- navigation.tabs
- navigation.indexes
- navigation.top
- navigation.footer
- toc.follow
- search.suggest
- search.highlight
- content.code.copy
- content.tabs.link
- content.action.edit
- content.action.view
nav:
- Home:
- index.md
- home/license.md
- "FAQ": home/faq.md
- home/exceptions.md
- Releases:
- 'Overview': home/releases/index.md
- 'Unreleased': home/releases/unreleased.md
- 'v3.12.0': home/releases/v3.12.0.md
- 'v3.11.3': home/releases/v3.11.3.md
- 'v3.11.2': home/releases/v3.11.2.md
- 'v3.11.1': home/releases/v3.11.1.md
- 'v3.11.0': home/releases/v3.11.0.md
- 'v3.10.5': home/releases/v3.10.5.md
- 'v3.10.4': home/releases/v3.10.4.md
- 'v3.10.3': home/releases/v3.10.3.md
- 'v3.10.2': home/releases/v3.10.2.md
- 'v3.10.1': home/releases/v3.10.1.md
- 'v3.10.0': home/releases/v3.10.0.md
- 'v3.9.1': home/releases/v3.9.1.md
- 'v3.9.0': home/releases/v3.9.0.md
- 'v3.8.0': home/releases/v3.8.0.md
- 'v3.7.3': home/releases/v3.7.3.md
- 'v3.7.2': home/releases/v3.7.2.md
- 'v3.7.1': home/releases/v3.7.1.md
- 'v3.7.0': home/releases/v3.7.0.md
- 'v3.6.1': home/releases/v3.6.1.md
- 'v3.6.0': home/releases/v3.6.0.md
- 'v3.5.0': home/releases/v3.5.0.md
- 'v3.4.0': home/releases/v3.4.0.md
- 'v3.3.0': home/releases/v3.3.0.md
- 'v3.2.0': home/releases/v3.2.0.md
- 'v3.1.2': home/releases/v3.1.2.md
- 'v3.1.1': home/releases/v3.1.1.md
- 'v3.1.0': home/releases/v3.1.0.md
- 'v3.0.1': home/releases/v3.0.1.md
- 'v3.0.0': home/releases/v3.0.0.md
- 'v2.1.1': home/releases/v2.1.1.md
- 'v2.1.0': home/releases/v2.1.0.md
- 'v2.0.10': home/releases/v2.0.10.md
- 'v2.0.9': home/releases/v2.0.9.md
- 'v2.0.8': home/releases/v2.0.8.md
- 'v2.0.7': home/releases/v2.0.7.md
- 'v2.0.6': home/releases/v2.0.6.md
- 'v2.0.5': home/releases/v2.0.5.md
- 'v2.0.4': home/releases/v2.0.4.md
- 'v2.0.3': home/releases/v2.0.3.md
- 'v2.0.2': home/releases/v2.0.2.md
- 'v2.0.1': home/releases/v2.0.1.md
- 'v2.0.0': home/releases/v2.0.0.md
- 'v1.1.0': home/releases/v1.1.0.md
- 'v1.0.0': home/releases/v1.0.0.md
- Blog:
- 'How 3.13.0 got faster': home/blog/how_3_13_0_got_faster.md
- home/design_goals.md
- home/architecture.md
- home/customers.md
- home/sponsors.md
- home/debugging.md
- Features:
- features/index.md
- features/arbitrary_types.md
- features/type_recipes.md
- Binary Formats:
- features/binary_formats/index.md
- features/binary_formats/bjdata.md
- features/binary_formats/bon8.md
- features/binary_formats/bson.md
- features/binary_formats/cbor.md
- features/binary_formats/messagepack.md
- features/binary_formats/ubjson.md
- features/binary_values.md
- features/comments.md
- features/conversions.md
- features/creating_values.md
- Element Access:
- features/element_access/index.md
- features/element_access/unchecked_access.md
- features/element_access/checked_access.md
- features/element_access/default_value.md
- features/files.md
- features/iterators.md
- features/merge_patch.md
- features/json_patch.md
- features/json_pointer.md
- features/modifying_values.md
- features/modules.md
- 'nlohmann Namespace': features/namespace.md
- features/no_exceptions.md
- features/object_order.md
- features/performance.md
- Parsing:
- features/parsing/index.md
- features/parsing/json_lines.md
- features/parsing/large_and_partial_input.md
- features/parsing/parse_exceptions.md
- features/parsing/parser_callbacks.md
- features/parsing/sax_interface.md
- features/parsing/untrusted_input.md
- features/assertions.md
- features/serialization.md
- features/enum_conversion.md
- features/macros.md
- features/trailing_commas.md
- Types:
- features/types/index.md
- features/types/number_handling.md
- features/types/template_parameters.md
- Zero-copy views:
- features/json_view/index.md
- features/json_view/lifetime.md
- features/json_view/differences.md
- features/json_view/reading.md
- features/json_view/generic_code.md
- features/json_view/editing.md
- features/json_view/images.md
- Integration:
- integration/index.md
- integration/migration_guide.md
- integration/cmake.md
- integration/package_managers.md
- integration/pkg-config.md
- integration/compile_times.md
- API Documentation:
- basic_json:
- 'Overview': api/basic_json/index.md
- '(Constructor)': api/basic_json/basic_json.md
- '(Destructor)': api/basic_json/~basic_json.md
- 'accept': api/basic_json/accept.md
- 'array': api/basic_json/array.md
- 'array_t': api/basic_json/array_t.md
- 'as_base_class': api/basic_json/as_base_class.md
- 'at': api/basic_json/at.md
- 'back': api/basic_json/back.md
- 'begin': api/basic_json/begin.md
- 'binary': api/basic_json/binary.md
- 'binary_t': api/basic_json/binary_t.md
- 'bjdata_version_t': api/basic_json/bjdata_version_t.md
- 'boolean_t': api/basic_json/boolean_t.md
- 'cbegin': api/basic_json/cbegin.md
- 'cbor_tag_handler_t': api/basic_json/cbor_tag_handler_t.md
- 'cend': api/basic_json/cend.md
- 'clear': api/basic_json/clear.md
- 'contains': api/basic_json/contains.md
- 'count': api/basic_json/count.md
- 'crbegin': api/basic_json/crbegin.md
- 'crend': api/basic_json/crend.md
- 'default_object_comparator_t': api/basic_json/default_object_comparator_t.md
- 'diff': api/basic_json/diff.md
- 'dump': api/basic_json/dump.md
- 'emplace': api/basic_json/emplace.md
- 'emplace_back': api/basic_json/emplace_back.md
- 'empty': api/basic_json/empty.md
- 'end': api/basic_json/end.md
- 'end_pos': api/basic_json/end_pos.md
- 'erase': api/basic_json/erase.md
- 'error_handler_t': api/basic_json/error_handler_t.md
- 'exception': api/basic_json/exception.md
- 'find': api/basic_json/find.md
- 'flatten': api/basic_json/flatten.md
- 'format_as': api/basic_json/format_as.md
- 'from_bjdata': api/basic_json/from_bjdata.md
- 'from_bon8': api/basic_json/from_bon8.md
- 'from_bson': api/basic_json/from_bson.md
- 'from_cbor': api/basic_json/from_cbor.md
- 'from_msgpack': api/basic_json/from_msgpack.md
- 'from_ubjson': api/basic_json/from_ubjson.md
- 'front': api/basic_json/front.md
- 'get': api/basic_json/get.md
- 'get_allocator': api/basic_json/get_allocator.md
- 'get_binary': api/basic_json/get_binary.md
- 'get_ptr': api/basic_json/get_ptr.md
- 'get_ref': api/basic_json/get_ref.md
- 'get_to': api/basic_json/get_to.md
- 'std::formatter&lt;basic_json&gt;': api/basic_json/std_formatter.md
- 'std::hash&lt;basic_json&gt;': api/basic_json/std_hash.md
- 'input_format_t': api/basic_json/input_format_t.md
- 'insert': api/basic_json/insert.md
- 'invalid_iterator': api/basic_json/invalid_iterator.md
- 'is_array': api/basic_json/is_array.md
- 'is_binary': api/basic_json/is_binary.md
- 'is_boolean': api/basic_json/is_boolean.md
- 'is_discarded': api/basic_json/is_discarded.md
- 'is_null': api/basic_json/is_null.md
- 'is_number': api/basic_json/is_number.md
- 'is_number_float': api/basic_json/is_number_float.md
- 'is_number_integer': api/basic_json/is_number_integer.md
- 'is_number_unsigned': api/basic_json/is_number_unsigned.md
- 'is_object': api/basic_json/is_object.md
- 'is_primitive': api/basic_json/is_primitive.md
- 'is_string': api/basic_json/is_string.md
- 'is_structured': api/basic_json/is_structured.md
- 'items': api/basic_json/items.md
- 'json_base_class_t': api/basic_json/json_base_class_t.md
- 'json_serializer': api/basic_json/json_serializer.md
- 'max_size': api/basic_json/max_size.md
- 'meta': api/basic_json/meta.md
- 'merge_diff': api/basic_json/merge_diff.md
- 'merge_patch': api/basic_json/merge_patch.md
- 'number_float_t': api/basic_json/number_float_t.md
- 'number_integer_t': api/basic_json/number_integer_t.md
- 'number_unsigned_t': api/basic_json/number_unsigned_t.md
- 'object': api/basic_json/object.md
- 'object_comparator_t': api/basic_json/object_comparator_t.md
- 'object_t': api/basic_json/object_t.md
- 'operator ValueType': api/basic_json/operator_ValueType.md
- 'operator value_t': api/basic_json/operator_value_t.md
- 'operator[]': api/basic_json/operator[].md
- 'operator=': api/basic_json/operator=.md
- 'operator+=': api/basic_json/operator+=.md
- 'operator==': api/basic_json/operator_eq.md
- 'operator!=': api/basic_json/operator_ne.md
- 'operator<': api/basic_json/operator_lt.md
- 'operator>': api/basic_json/operator_gt.md
- 'operator<=': api/basic_json/operator_le.md
- 'operator>=': api/basic_json/operator_ge.md
- 'operator<=>': api/basic_json/operator_spaceship.md
- 'out_of_range': api/basic_json/out_of_range.md
- 'other_error': api/basic_json/other_error.md
- 'parse': api/basic_json/parse.md
- 'parse_error': api/basic_json/parse_error.md
- 'parse_event_t': api/basic_json/parse_event_t.md
- 'parser_callback_t': api/basic_json/parser_callback_t.md
- 'patch': api/basic_json/patch.md
- 'patch_inplace': api/basic_json/patch_inplace.md
- 'push_back': api/basic_json/push_back.md
- 'rbegin': api/basic_json/rbegin.md
- 'rend': api/basic_json/rend.md
- 'sax_parse': api/basic_json/sax_parse.md
- 'size': api/basic_json/size.md
- 'start_pos': api/basic_json/start_pos.md
- 'string_t': api/basic_json/string_t.md
- 'swap': api/basic_json/swap.md
- 'std::swap&lt;basic_json&gt;': api/basic_json/std_swap.md
- 'to_bjdata': api/basic_json/to_bjdata.md
- 'to_bon8': api/basic_json/to_bon8.md
- 'to_bson': api/basic_json/to_bson.md
- 'to_cbor': api/basic_json/to_cbor.md
- 'to_msgpack': api/basic_json/to_msgpack.md
- 'to_string': api/basic_json/to_string.md
- 'to_ubjson': api/basic_json/to_ubjson.md
- 'type': api/basic_json/type.md
- 'type_error': api/basic_json/type_error.md
- 'type_name': api/basic_json/type_name.md
- 'unflatten': api/basic_json/unflatten.md
- 'update': api/basic_json/update.md
- 'value': api/basic_json/value.md
- 'value_t': api/basic_json/value_t.md
- 'with_t': api/basic_json/with_t.md
- basic_json_document:
- 'Overview': api/basic_json_document/index.md
- '(Constructor)': api/basic_json_document/basic_json_document.md
- 'accept': api/basic_json_document/accept.md
- 'erase': api/basic_json_document/erase.md
- 'insert': api/basic_json_document/insert.md
- 'is_discarded': api/basic_json_document/is_discarded.md
- 'load': api/basic_json_document/load.md
- 'memory_usage': api/basic_json_document/memory_usage.md
- 'node_count': api/basic_json_document/node_count.md
- 'owns_source': api/basic_json_document/owns_source.md
- 'parse': api/basic_json_document/parse.md
- 'parse_copy': api/basic_json_document/parse_copy.md
- 'push_back': api/basic_json_document/push_back.md
- 'read': api/basic_json_document/read.md
- 'root': api/basic_json_document/root.md
- 'save': api/basic_json_document/save.md
- 'set': api/basic_json_document/set.md
- 'shrink_to_fit': api/basic_json_document/shrink_to_fit.md
- 'source': api/basic_json_document/source.md
- basic_json_view:
- 'Overview': api/basic_json_view/index.md
- '(Constructor)': api/basic_json_view/basic_json_view.md
- 'at': api/basic_json_view/at.md
- 'back': api/basic_json_view/back.md
- 'begin': api/basic_json_view/begin.md
- 'cbegin': api/basic_json_view/cbegin.md
- 'cend': api/basic_json_view/cend.md
- 'contains': api/basic_json_view/contains.md
- 'count': api/basic_json_view/count.md
- 'dump': api/basic_json_view/dump.md
- 'empty': api/basic_json_view/empty.md
- 'end': api/basic_json_view/end.md
- 'find': api/basic_json_view/find.md
- 'front': api/basic_json_view/front.md
- 'get': api/basic_json_view/get.md
- 'get_string': api/basic_json_view/get_string.md
- 'get_to': api/basic_json_view/get_to.md
- 'is_array': api/basic_json_view/is_array.md
- 'is_binary': api/basic_json_view/is_binary.md
- 'is_boolean': api/basic_json_view/is_boolean.md
- 'is_discarded': api/basic_json_view/is_discarded.md
- 'is_null': api/basic_json_view/is_null.md
- 'is_number': api/basic_json_view/is_number.md
- 'is_number_float': api/basic_json_view/is_number_float.md
- 'is_number_integer': api/basic_json_view/is_number_integer.md
- 'is_number_unsigned': api/basic_json_view/is_number_unsigned.md
- 'is_object': api/basic_json_view/is_object.md
- 'is_primitive': api/basic_json_view/is_primitive.md
- 'is_string': api/basic_json_view/is_string.md
- 'is_structured': api/basic_json_view/is_structured.md
- 'items': api/basic_json_view/items.md
- 'materialize': api/basic_json_view/materialize.md
- 'number_format': api/basic_json_view/number_format.md
- 'number_token': api/basic_json_view/number_token.md
- 'operator<<': api/basic_json_view/operator_ltlt.md
- 'operator[]': api/basic_json_view/operator[].md
- 'operator==': api/basic_json_view/operator_eq.md
- 'operator!=': api/basic_json_view/operator_ne.md
- 'size': api/basic_json_view/size.md
- 'source_offset': api/basic_json_view/source_offset.md
- 'type': api/basic_json_view/type.md
- 'type_name': api/basic_json_view/type_name.md
- 'value': api/basic_json_view/value.md
- byte_container_with_subtype:
- 'Overview': api/byte_container_with_subtype/index.md
- '(constructor)': api/byte_container_with_subtype/byte_container_with_subtype.md
- 'clear_subtype': api/byte_container_with_subtype/clear_subtype.md
- 'has_subtype': api/byte_container_with_subtype/has_subtype.md
- 'operator==': api/byte_container_with_subtype/operator_eq.md
- 'operator!=': api/byte_container_with_subtype/operator_ne.md
- 'set_subtype': api/byte_container_with_subtype/set_subtype.md
- 'subtype': api/byte_container_with_subtype/subtype.md
- adl_serializer:
- 'Overview': api/adl_serializer/index.md
- 'from_json': api/adl_serializer/from_json.md
- 'to_json': api/adl_serializer/to_json.md
- 'is_json_view': api/is_json_view.md
- 'json': api/json.md
- 'json_document': api/json_document.md
- 'json_editable_document': api/json_editable_document.md
- 'json_editable_view': api/json_editable_view.md
- json_pointer:
- 'Overview': api/json_pointer/index.md
- '(Constructor)': api/json_pointer/json_pointer.md
- 'back': api/json_pointer/back.md
- 'empty': api/json_pointer/empty.md
- 'front': api/json_pointer/front.md
- 'operator string_t': api/json_pointer/operator_string_t.md
- 'operator==': api/json_pointer/operator_eq.md
- 'operator!=': api/json_pointer/operator_ne.md
- 'operator<=>': api/json_pointer/operator_spaceship.md
- 'operator/': api/json_pointer/operator_slash.md
- 'operator/=': api/json_pointer/operator_slasheq.md
- 'parent_pointer': api/json_pointer/parent_pointer.md
- 'pop_back': api/json_pointer/pop_back.md
- 'pop_front': api/json_pointer/pop_front.md
- 'push_back': api/json_pointer/push_back.md
- 'push_front': api/json_pointer/push_front.md
- 'string_t': api/json_pointer/string_t.md
- 'to_string': api/json_pointer/to_string.md
- json_sax:
- 'Overview': api/json_sax/index.md
- 'binary': api/json_sax/binary.md
- 'boolean': api/json_sax/boolean.md
- 'end_array': api/json_sax/end_array.md
- 'end_object': api/json_sax/end_object.md
- 'key': api/json_sax/key.md
- 'null': api/json_sax/null.md
- 'number_float': api/json_sax/number_float.md
- 'number_integer': api/json_sax/number_integer.md
- 'number_unsigned': api/json_sax/number_unsigned.md
- 'parse_error': api/json_sax/parse_error.md
- 'start_array': api/json_sax/start_array.md
- 'start_object': api/json_sax/start_object.md
- 'string': api/json_sax/string.md
- 'json_view': api/json_view.md
- 'operator<<(basic_json), operator<<(json_pointer)': api/operator_ltlt.md
- 'operator>>(basic_json)': api/operator_gtgt.md
- 'operator""_json': api/operator_literal_json.md
- 'operator""_json_pointer': api/operator_literal_json_pointer.md
- 'ordered_json': api/ordered_json.md
- 'ordered_json_document': api/ordered_json_document.md
- 'ordered_json_editable_document': api/ordered_json_editable_document.md
- 'ordered_json_editable_view': api/ordered_json_editable_view.md
- 'ordered_json_view': api/ordered_json_view.md
- 'ordered_map': api/ordered_map.md
- 'view_mode': api/view_mode.md
- macros:
- 'Overview': api/macros/index.md
- 'JSON_ASSERT': api/macros/json_assert.md
- 'JSON_BRACE_INIT_COPY_SEMANTICS': api/macros/json_brace_init_copy_semantics.md
- 'JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER': api/macros/json_throw_user.md
- 'JSON_DIAGNOSTICS': api/macros/json_diagnostics.md
- 'JSON_DELETE_DEPRECATED_FUNCTIONS': api/macros/json_delete_deprecated_functions.md
- 'JSON_DIAGNOSTIC_POSITIONS': api/macros/json_diagnostic_positions.md
- 'JSON_DISABLE_ENUM_SERIALIZATION': api/macros/json_disable_enum_serialization.md
- 'JSON_DISABLE_STREAM_BULK_SCAN': api/macros/json_disable_stream_bulk_scan.md
- 'JSON_DISABLE_TUPLE_REFERENCE_CONVERSION': api/macros/json_disable_tuple_reference_conversion.md
- 'JSON_DISABLE_UNLOCKED_FILE_IO': api/macros/json_disable_unlocked_file_io.md
- 'JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20, JSON_HAS_CPP_23, JSON_HAS_CPP_26': api/macros/json_has_cpp_11.md
- 'JSON_HAS_EXPERIMENTAL_FILESYSTEM, JSON_HAS_FILESYSTEM': api/macros/json_has_filesystem.md
- 'JSON_HAS_RANGE_VIEW_CONVERSION': api/macros/json_has_range_view_conversion.md
- 'JSON_HAS_RANGES': api/macros/json_has_ranges.md
- 'JSON_HAS_STATIC_RTTI': api/macros/json_has_static_rtti.md
- 'JSON_HAS_STD_FORMAT': api/macros/json_has_std_format.md
- 'JSON_HAS_THREE_WAY_COMPARISON': api/macros/json_has_three_way_comparison.md
- 'JSON_NO_AUTOMATIC_UDLS': api/macros/json_no_automatic_udls.md
- 'JSON_NOEXCEPTION': api/macros/json_noexception.md
- 'JSON_NO_IO': api/macros/json_no_io.md
- 'JSON_NO_SIMD': api/macros/json_no_simd.md
- 'JSON_NO_THREAD_LOCAL': api/macros/json_no_thread_local.md
- 'JSON_PRECISE_STREAM_POSITION': api/macros/json_precise_stream_position.md
- 'JSON_RECURSION_DEPTH_LIMIT': api/macros/json_recursion_depth_limit.md
- 'JSON_SKIP_LIBRARY_VERSION_CHECK': api/macros/json_skip_library_version_check.md
- 'JSON_SKIP_UNSUPPORTED_COMPILER_CHECK': api/macros/json_skip_unsupported_compiler_check.md
- 'JSON_STRICT_BINARY_UTF8': api/macros/json_strict_binary_utf8.md
- 'JSON_STRICT_NUL_HANDLING': api/macros/json_strict_nul_handling.md
- 'JSON_UBJSON_VALUELESS_ELEMENTS_PER_BYTE': api/macros/json_ubjson_valueless_elements_per_byte.md
- 'JSON_USE_GLOBAL_UDLS': api/macros/json_use_global_udls.md
- 'JSON_USE_IMPLICIT_CONVERSIONS': api/macros/json_use_implicit_conversions.md
- 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
- 'JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS': api/macros/json_use_objects_for_enum_keyed_maps.md
- 'JSON_USE_SIMDUTF': api/macros/json_use_simdutf.md
- 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
- 'NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_intrusive.md
- 'NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_non_intrusive.md
- 'NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES': api/macros/nlohmann_define_type_with_names.md
- 'NLOHMANN_JSON_NAMESPACE': api/macros/nlohmann_json_namespace.md
- 'NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END': api/macros/nlohmann_json_namespace_begin.md
- 'NLOHMANN_JSON_NAMESPACE_NO_VERSION': api/macros/nlohmann_json_namespace_no_version.md
- 'NLOHMANN_JSON_SERIALIZE_ENUM': api/macros/nlohmann_json_serialize_enum.md
- 'NLOHMANN_JSON_SERIALIZE_ENUM_STRICT': api/macros/nlohmann_json_serialize_enum_strict.md
- 'NLOHMANN_JSON_VERSION_MAJOR, NLOHMANN_JSON_VERSION_MINOR, NLOHMANN_JSON_VERSION_PATCH': api/macros/nlohmann_json_version_major.md
- Community:
- community/index.md
- community/ecosystem.md
- "Code of Conduct": community/code_of_conduct.md
- community/contribution_guidelines.md
- community/quality_assurance.md
- community/governance.md
- community/roadmap.md
- community/security_policy.md
- community/assurance_case.md
# Extras
extra:
social:
- icon: fontawesome/brands/github
link: https://github.com/nlohmann
- icon: fontawesome/brands/linkedin
link: https://www.linkedin.com/in/nielslohmann/
- icon: fontawesome/brands/xing
link: https://www.xing.com/profile/Niels_Lohmann
- icon: fontawesome/brands/paypal
link: https://www.paypal.me/nlohmann
generator: false
# Extensions
markdown_extensions:
- abbr
- admonition
- attr_list
- def_list
- codehilite:
guess_lang: false
- toc:
permalink: true
- md_in_html
- pymdownx.betterem:
smart_enable: all
- pymdownx.caret
- pymdownx.critic
- pymdownx.details
- pymdownx.emoji:
emoji_index: !!python/name:material.extensions.emoji.twemoji
emoji_generator: !!python/name:material.extensions.emoji.to_svg
- pymdownx.inlinehilite
- pymdownx.magiclink
- pymdownx.mark
#- pymdownx.smartsymbols
- pymdownx.superfences:
custom_fences:
- name: mermaid
class: mermaid
format: !!python/name:pymdownx.superfences.fence_code_format
- pymdownx.tasklist:
custom_checkbox: true
- pymdownx.tabbed:
alternate_style: true
- pymdownx.tilde
- pymdownx.snippets:
base_path: docs
check_paths: true
restrict_base_path: false # needed to allow including files from the .github folder
auto_append:
- ../includes/glossary.md
# report broken links, anchors, and nav entries as warnings, so that `mkdocs build --strict` (make build) fails
validation:
nav:
omitted_files: warn
not_found: warn
absolute_links: warn
links:
not_found: warn
anchors: warn
absolute_links: warn
unrecognized_links: warn
hooks:
- hooks/api_changes.py
- hooks/copy_markdown_source.py
- hooks/unreleased_versions.py
plugins:
- search:
separator: '[\s\-\.]'
lang: en
- minify:
minify_html: true
- git-revision-date-localized:
strict: false # log "has no git logs" for uncommitted pages as info, not as a warning
- redirects:
redirect_maps:
'api/basic_json/operator_gtgt.md': api/operator_gtgt.md
'api/basic_json/operator_ltlt.md': api/operator_ltlt.md
'api/basic_json/operator_literal_json.md': api/operator_literal_json.md
'api/basic_json/operator_literal_json_pointer.md': api/operator_literal_json_pointer.md
'api/json_pointer/operator_string.md': api/json_pointer/operator_string_t.md
'home/code_of_conduct.md': community/code_of_conduct.md
- htmlproofer: # see https://github.com/manuzhang/mkdocs-htmlproofer-plugin
enabled: !ENV [ENABLED_HTMLPROOFER, False]
raise_error_after_finish: true # log every broken link, then fail
skip_downloads: true # check headers only (customers.md links large PDFs)
raise_error_excludes: # integer status codes, fnmatch patterns
403: ['*'] # bot protection against the plugin's "Bot <uuid>" user agent
429: ['*'] # rate limiting (hundreds of github.com URLs)
502: ['*']
503: ['*']
504: ['*'] # timeouts are reported as 504
-1: # connection errors
- 'https://repology.org/*' # repology.org is suspended since 2026-09
- 'http://2ak5ape.257.cz/' # customers.md: kept although unreachable
400: ['https://www.meta.com/*'] # customers.md: answers the plugin's user agent with 400, browsers with 200
401:
- 'https://fossies.org/*' # answers the plugin's user agent with 401, browsers and curl with 200
- 'https://mysupport.razer.com/*' # customers.md: same, browsers answer 200
419: ['https://news.ycombinator.com/*'] # answers the plugin's user agent with 419, browsers with 200
404:
- 'https://gitlab.b-data.ch/*' # answers the plugin's user agent with 404, browsers with 200
# customers.md: kept although dead
- 'https://www.cisco.com/c/dam/en_us/about/doing_business/open_source/docs/CiscoWebexDeskCamera-23-1622100417.pdf'
- 'https://docs.cyberark.com/Downloads/Legal/Privileged%20Session%20Manager%20for%20SSH%20Third-Party%20Notices.pdf'
- 'https://docs.citrix.com/en-us/provisioning/2203-ltsr/downloads/pvs-third-party-notices-2203.pdf'
- 'https://docs.citrix.com/en-us/citrix-virtual-apps-desktops/2305/downloads/third-party-notices-apps-and-desktops.pdf'
500: ['https://marne.io/licenses'] # customers.md: kept although dead
ignore_urls:
- mailto:*
- privacy:
# repology.org refuses requests from GitHub Actions runners, which made
# the privacy plugin abort the whole build when it could not download the
# package badges (the fetch fails, then reading the missing cache entry
# raises FileNotFoundError). Readers' browsers are served normally, so
# leave these badges as external references instead of self-hosting them.
# The same goes for img.shields.io, whose version badges time out from
# time to time (strict mode turns the failed download into an error) and
# would go stale between builds if they were self-hosted anyway.
assets_exclude:
- repology.org/*
- img.shields.io/*
- llmstxt:
markdown_description: >
JSON for Modern C++ is a C++11 header-only library implementing a JSON
value type with an STL-like API, JSON Pointer/Patch, CBOR/MessagePack/
BSON/UBJSON/BJData/BON8 binary format support, and a SAX-style parser interface.
sections:
Home:
- index.md
- home/*.md
- home/blog/*.md
Features:
- features/*.md
- features/binary_formats/*.md
- features/element_access/*.md
- features/parsing/*.md
- features/types/*.md
Integration:
- integration/*.md
API Documentation:
- api/*.md
- api/basic_json/*.md
- api/basic_json_document/*.md
- api/basic_json_view/*.md
- api/adl_serializer/*.md
- api/byte_container_with_subtype/*.md
- api/json_pointer/*.md
- api/json_sax/*.md
- api/macros/*.md
Community:
- community/*.md
extra_css:
- css/custom.css
- css/brand.css
- css/fig-sax.css
- css/fig-jsonview.css
- css/fig-exceptions.css
- css/fig-pointer.css
- css/fig-charts.css
- css/fig-integration.css
- css/fig-macros.css
extra_javascript:
- js/mermaid-brand.js
- js/external-links.js
- js/fig-sax.js
- js/fig-jsonview.js
- js/fig-exceptions.js
- js/fig-pointer.js
- js/fig-charts.js
- js/fig-integration.js
- js/fig-macros.js
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