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Niels Lohmann 4c3a3eb5b5 Add dump() and comparisons to json_view (#5624) 
* Add dump() and comparisons to json_view

Add basic_json_view::dump() and the comparison operators, and read
floats from the parser's digit layout instead of rescanning the
token.

dump(indent, indent_char, ensure_ascii, number_format) writes a
value the way ordered_json::parse(text).dump() writes it for the
same arguments: members in document order, all of them should a
key occur more than once; strings escaped by the same rules, using
the library's scanning kernels; floats written with the library's
to_chars conversion, so the output equals basic_json's byte for
byte; integers copied from the source, where they are already
canonical, except -0, which parse() reads as 0. There is no
error_handler argument, because the view only holds valid UTF-8.
number_format::source copies numbers exactly as they appear in the
source (e.g. "1.50", "1E2", "-0"), which basic_json cannot provide.
operator<< takes the indentation from the stream width, as for
basic_json. The writer walks iteratively, so nesting depth is
limited by memory only.

operator== and operator!= compare two views, or a view and a
basic_json value in either order, by the rules basic_json's
operator== uses: numbers compare by value across their types,
objects compare by their members with duplicate keys resolved as
parse() resolves them, member order matters only where the object
type keeps one, and discarded views compare as discarded basic_json
values do, including under JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON.
Nothing is materialized except single scalars.

While parsing, the view now records where the integer digits, the
fraction digits, and the exponent of a float token are, so floats
and doubles with at most 19 digits are read from that layout with
the library's decimal_to_float() instead of rescanning the token.
Both round correctly, so the values are those of parse(). get<double>(),
materialize(), dump(), and the comparisons all use it.

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

* Avoid raw string with escapes inside CHECK macro (MSVC C2017)

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

* Size the dump buffer of a small value by its own extent

The source extent of a value was read from the next node, falling back to the rest of the document when that node held a decoded string. dump() of a small value could thus allocate a buffer as large as the document. Skip a few such nodes, cap the fallback estimate, and shrink a buffer that is much larger than its output.

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

* Hold the documents of the dump and comparison tests in names

root() of a temporary document is deleted: its views would dangle.

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

* Do not shrink the output of dump()

finish() copied the whole output when the buffer was more than twice as
large as the result (citm dump +11%). The tighter source_extent()
estimate already keeps the buffer of a small value small.

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

* Document and test first-wins lookups next to dump() and ==

dump() writes every member and == resolves duplicate keys as parse()
does, whereas lookups find the first member of a duplicate key.

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

* Fix the clang-tidy 22 findings in json_view and its tests

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

* Split the dump and comparison tests off unit-json_view.cpp

The MinGW linker of the Windows clang jobs cannot link object files with more
than 32767 sections ("relocation truncated to fit: IMAGE_REL_AMD64_REL32
against `.rdata'"). unit-json_view.cpp reaches that limit as the stack
grows, so its "json_view dump" and "json_view comparison" test cases move
into unit-json_view_dump.cpp. The test generator and has_duplicate_keys()
that both files use move into json_view_test_helpers.hpp.

The new file mentions JSON_HAS_CPP_17, so it is built for C++17 like the file
it was split from.

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

* Make json_view.hpp pass include-what-you-use

ci_single_binaries runs IWYU with --error on every header. For json_view.hpp
it suggested adding <array> (std::array is used), the headers that json.hpp
already provides (abi_config, abi_macros, input_adapters, json_pointer,
cpp_future, string_concat, value_t, json_fwd), and <version> for
std::nullptr_t, and removing <cstddef>.

- include <array>
- keep <cstddef> (nullptr_t, size_t; IWYU attributes them to <version> and <cstring>)
- tell IWYU not to suggest the headers that json.hpp provides: the amalgamated
  json_view.hpp only includes json.hpp, so including them here would duplicate
  their definitions

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

* Regenerate the amalgamated headers

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

* Follow the renames from the review of the view builder

The review of #5620 renamed document_data's tape/tape_size/tape_cap to
nodes/node_count/node_capacity and made the decode arena a
std::vector<char>; adapt the code of this change to it.

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

* Keep the stream includes of json_view.hpp for IWYU

json_view.hpp uses std::istream and std::ostream itself, but IWYU sees
them through the exported json.hpp and asked to remove both includes,
which fails ci_single_binaries (single_json_view).

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

* Address the review of json_view dump() and comparisons

From gregmarr's review of #5624:

- The output buffer takes string literals without a length.
- write_float() names the IEEE single/double condition once, as the
  library's serializer does.
- equal() checks the types first and compares with !=; the reference to
  the top frame is noted as dangling after pop_back().
- dump.md: one paragraph per case in the notes.

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

* Regenerate the amalgamated headers

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

* Exclude all json_view test files from Infer's reports

The same std::unique_ptr false positive (USE_AFTER_DELETE) also shows for
two json_documents parsed in one lambda in unit-json_view_dump.cpp
(ci_infer). It affects any test that holds several documents, so the
exclusion now covers tests/src/unit-json_view*.cpp; ASan and Valgrind
cover these tests.

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

* Allow the string literal parameter of the view serializer's put() for clang-tidy

The overload takes the literal by array reference so that its length is a
template parameter, like scan_literal() and the C array overloads of
to_json() and from_json().

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

* Bind the serializer's frame only after the check for its end

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

* Regenerate the amalgamated headers

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-21 10:21:28 +02:00
Niels Lohmann 43e97b629b Add element access, iteration, values, and JSON pointers to json_view (#5622) 
* Add element access, iteration, values, and JSON pointers to json_view

Give basic_json_view the read-only access functions of basic_json:
operator[] and at() with keys and indices, front()/back(), find(),
contains(), count(), begin()/end() and cbegin()/cend(), items()
with structured bindings from C++17 on, and type_name().

Exceptions have the ids and messages of the const functions of
basic_json. Where basic_json has undefined behavior the view
answers safely: operator[] with a missing key or an out-of-range
index returns a discarded view, and front()/back() of an empty
container throw invalid_iterator.214. Objects are iterated in
document order, and all members are visited; duplicate-key lookups
find the first member (as yyjson and simdjson do), while parse(),
materialize(), and the map conversions keep the last value, as
parse() does. Keys of up to 16 bytes are compared with two
overlapping loads.

Add value conversions: get<T>()/get_to() for arithmetic types,
bool, nullptr_t, strings (std::basic_string copied,
string_view_t without a copy), BasicJsonType, views, std::vector,
and maps with string keys; get_string() for the string without a
copy; number_token() for the number exactly as written in the
source; value() with keys and JSON pointers; and operator[]/at()/
contains() with JSON pointers. Everything else, including types
with from_json(), goes through materialize() of that subtree.
get<T>() of arithmetic types is inlined down to the conversion, so
reading an integer needs no call.

detail::json_pointer_access exposes a pointer's reference tokens
to code outside basic_json.

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

* Make view lookups last-wins and chained access safe

* Lookups (operator[], at, find, contains, count, value, JSON pointers)
  return the last member of a duplicate key, as materialize() and
  parse() keep it.
* operator[] on a discarded view returns a discarded view instead of
  throwing, so v["a"]["b"] is safe for a missing "a".
* operator[] and at() take any integer type (not only int and size_t),
  fixing ambiguous calls with unsigned, long, std::int64_t, ...
* Fix the operator[] documentation, which claimed a discarded view for
  a type mismatch where type_error.305 is thrown.

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

* Replace the removed operator bool of basic_json_view in the header and its tests

A view is tested with is_discarded(); the lookups in at(), value() and
contains(json_pointer) and the unit tests no longer rely on the explicit
conversion to bool.

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

* Use named documents in the json_view tests that called root() on a temporary

root() of an rvalue document is deleted, because the views would dangle.

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

* Test discarded views with is_discarded() in the operator[] docs and examples

The explicit conversion to bool of basic_json_view is gone.

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

* Return the first member of duplicate keys from lookups again

Looking up the last member of a duplicate key cannot stop at a match, so
every lookup scanned the whole object (1.6 to 3.4 times slower for small
objects). operator[](key), at, find, value, contains, count, and JSON
pointer resolution return the first member again, as yyjson and simdjson
do; materialize() and get<map>() keep the last value, as parse().

The documentation says so in the feature page and on each lookup page,
and explains how to get the value parse() would give. The integer index
templates and the discarded chaining of operator[] stay.

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

* Do not force-inline the view's functions on MSVC

__forceinline makes MSVC report C4714 for function templates it cannot
inline (get<std::string>), an error under /WX. The forced inlining is
only a performance hint, so use plain inline there.

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

* Make json_view.hpp pass include-what-you-use

Mark the includes that are needed by design (json.hpp, the macro
unscope, <tuple> for the tuple_size specialization), take size_t from
<cstring>, and drop the forward declaration of basic_json_document that
the friend declaration makes redundant.

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

* Avoid GCC useless-cast warnings in the integer index tests

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

* Make json_view.hpp pass include-what-you-use

ci_single_binaries runs IWYU with --error on every header. For json_view.hpp
it suggested adding <array> (std::array is used), the headers that json.hpp
already provides (abi_config, abi_macros, input_adapters, json_pointer,
cpp_future, string_concat, value_t, json_fwd), and <version> for
std::nullptr_t, and removing <cstddef>.

- include <array>
- keep <cstddef> (nullptr_t, size_t; IWYU attributes them to <version> and <cstring>)
- tell IWYU not to suggest the headers that json.hpp provides: the amalgamated
  json_view.hpp only includes json.hpp, so including them here would duplicate
  their definitions

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

* Fix the clang-tidy 22 findings in json_view and its tests

The same changes as on the dump branch, where they were first made, so
that this branch passes clang-tidy on its own.

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

* Regenerate the amalgamated headers

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

* Report one-character non-numeric array indices like basic_json in the view

Develop's #5800 made basic_json report a JSON pointer array index such as
"/a" as parse_error.109 instead of out_of_range.404, as longer ones were;
the view's array_index() follows, with "-" and the empty token still
unresolved.

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

* Address the review of json_view element access

From gregmarr's review of #5622:

- count() counts every member with the key, so count(key) > 1 detects
  duplicate keys; it was contains() as 0/1 before.
- get_to() passes types that get<T>() does not convert directly to
  from_json with the existing value, as basic_json::get_to() does, so that
  a from_json which sets only the fields present keeps the others.
- array_index() checks the empty token and "-" first; the results are
  unchanged.
- Docs: no "if an exception is thrown" where a view never changes
  anything; the borrowed source must also stay unmodified; items() on a
  temporary view is safe; back()/front() notes shortened; the basic_json
  see-also entries say how the view's results can differ.

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

* Regenerate the amalgamated headers

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

* Count matching keys as unsigned in the json_view access test

The conditional added 1 or 0 as int to a std::size_t, which GCC rejects
with -Werror=sign-conversion (ci_test_standards_gcc).

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

* Address the second review round of json_view element access

From gregmarr's review of #5622:

- begin()/end(): "a null value or a discarded view iterates as an empty
  range", singular like the primitive case before it.
- The class page's list of function groups has no trailing commas.
- document_data::key_equals() compares a key node with a string, for the
  key comparisons that were spelled out in each lookup.

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

* Regenerate the amalgamated headers

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

* Write the negated enable_if conditions of json_view with negation<>

With a ! or && in the condition, astyle spaces the whole template
header (template < ... >); detail::negation and a named trait keep it
compact, as the library writes such conditions elsewhere. From gregmarr's
review of #5630.

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

* Regenerate the amalgamated headers

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

* Keep detail::negation out of json_view.hpp's enable_ifs

include-what-you-use asks json_view.hpp to include
detail/meta/type_traits.hpp for it, which the single header must not do
(the amalgamation would duplicate json's internals). The two conditions of
value() go through a trait in value.hpp, like the others.

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

* Regenerate the amalgamated headers

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-21 10:21:27 +02:00
Niels Lohmann 122d718330 Add json_document and json_view: node index, parser, and document (#5620) 
* Add json_document and json_view: node index, parser, and document

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>

* Fix document_data for old Clang (3.4-3.6)

Drop the empty braced NSDMIs of the std::string members: old Clang
rejects the defaulted constructor when it is used by a member
initializer before the end of the class definition.

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

* Exclude libstdc++'s string_view comparison from the sign-change check

basic_string_view::_S_compare stores the difference of two lengths in a
signed difference_type on purpose, which -fsanitize=integer reports for
every comparison with a shorter view (test-json_view_cpp17).

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

* Reject integer lengths in json_document::parse

parse(ptr, len) compiled: len converted to allow_exceptions, and ptr was
read as a C string, past the end of a buffer without a terminating NUL.
Delete the overloads of parse, parse_copy, accept, and read that take an
integer other than bool where the flags are expected.

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

* Copy const rvalue strings and document the accepted inputs

json_document::parse(std::move(const_string)) failed to compile with
"no matching read_kind": only a non-const rvalue std::string can be moved
from. Treat a const rvalue as a copied byte container.

parse() does not accept everything BasicJsonType::parse() does: a FILE*
and pointers to or arrays of wide characters are rejected at compile time.
List the supported inputs instead.

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

* Remove the conversion to bool from json_view

explicit operator bool meant "refers to a value", which silently differs
from what a basic_json converts to. Use !v.is_discarded() instead.

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

* Delete json_document::root() on temporary documents

auto v = json_document::parse(text).root() compiled and left the view
dangling. Delete the overload for rvalue documents, take a named document
in the tests, and document the lifetime rule.

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

* Store node integers by halves on big-endian targets

The non-little-endian path of the node writer wrote the integer's native
word over len and next, so len got the high half there. Compose and split
the value explicitly (len is the low half, next the high half); the
little-endian path stays a plain memcpy.

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

* Check the node array size for overflow

reserve(n) and the growth of the index computed n * sizeof(node) without a
check, which wraps around on 32-bit targets for inputs of about 1 GiB and
allocates a too small array. Throw std::bad_alloc for a count beyond the
address space and clamp the growth step to it.

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

* State the exact input size limit of json_document

The check rejects inputs of 0xFFFFFFF0 bytes or more, but the exception
message and the documentation said 4 GiB. Name the limit once
(max_input_size), and state 4 GiB minus 16 bytes in the message and the
documentation. Test the limit with a container that only claims the size.

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

* Remove the unused legacy_discarded_value_comparison from abi_config

Nothing reads it: the view does not compare values.

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

* Align the banner comment of json_view.hpp

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

* Fuzz json_document with exact-size buffers and parse options

The fuzzer only parsed a std::string with default options. Also parse an
exact-size byte vector, which has no NUL after its last byte and takes the
bounds-checked path, and derive ignore_comments and ignore_trailing_commas
from the first input byte, comparing against json::parse and json::accept
with the same options.

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

* Give document_data a user-provided constructor

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

* Fix clang-tidy findings in unit-json_view_builder.cpp

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

* Annotate intentional patterns in unit-json_view.cpp for clang-tidy

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

* Suppress Flawfinder's read() finding on the deleted overload

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

* Check the steps of the deep-nesting test separately

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

* Make max_input_size a function (GCC -Wunused-const-variable)

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

* Make json_view.hpp pass include-what-you-use

ci_single_binaries runs IWYU with --error on every header. For json_view.hpp
it suggested adding <array> (std::array is used), the headers that json.hpp
already provides (abi_config, abi_macros, input_adapters, json_pointer,
cpp_future, string_concat, value_t, json_fwd), and <version> for
std::nullptr_t, and removing <cstddef>.

- include <array>
- keep <cstddef> (nullptr_t, size_t; IWYU attributes them to <version> and <cstring>)
- tell IWYU not to suggest the headers that json.hpp provides: the amalgamated
  json_view.hpp only includes json.hpp, so including them here would duplicate
  their definitions
- export json.hpp, keep macro_unscope.hpp, and drop the unused forward declaration of the document class

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

* Read the node array base after emit() in the view builder's open()

emit() moves the node array when it grows, and the subtraction read base
in the same expression, so the order was unspecified. MSVC Release builds
without forced inlining read the old base; the container index then
pointed outside the array and close() wrote out of bounds.

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

* Silence a clang-tidy use-after-move finding in the json_view test

const_text is const, so std::move does not move from it; the second call
is part of the const rvalue test.

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

* Regenerate the amalgamated headers

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

* Address the review of the view builder and document

Changes promised in the replies to the review of #5620:

- read() reuses the owned copy: a copied input (an rvalue byte container,
  a stream, FILE*, wide characters, an iterator range) is appended to the
  cleared owned buffer instead of a fresh std::string being move-assigned
  over it. A moved-in std::string still replaces it.
- The error replay runs the library parser with a SAX handler that stores
  nothing and throws the reported exception, instead of
  BasicJsonType::parse(), which built a DOM up to the error.
- Pointers to and arrays of wide characters, and FILE*, take the input
  adapter path (converted to UTF-8 into an owned buffer) instead of
  failing a static_assert. Wide pointers are NUL-terminated.
- Streams are read in blocks through rdbuf() into the buffer, instead of
  character by character through the input adapter; eofbit is set at the
  end, as by the library's stream adapter.
- tape/tape_size/tape_cap are now nodes/node_count/node_capacity.
- The builder's members get descriptive, m_-prefixed names.
- The shallow frame stack is a std::array (in a wrapper with a
  user-provided constructor: -Weffc++ wants the member initialized, and
  value-initializing the 64 frames costs up to 30 % on small documents).
- The value dispatch macro has no NEXT parameter; the switch is left with
  break, and the macro is undefined after its last use.
- literal() and digits_exceed() deduce the length from the string literal;
  each literal has one helper; the two `if (!is_float)` blocks are merged.
- arena_ensure() sits right before the writes; the decode arena is a
  std::vector<char>.
- The builder records the deepest nesting, and materialize() sizes its
  stack from it once (growing it only if a subtree is deeper).
- Comment fixes (hex4, slow_string, the NUL rule, put_utf8, 0 - m, the
  arena resize, grow()) and formatting (macro backslashes, digit cases,
  one power of ten per line, value_t assertion next to is_container()).
- build_with's template parameters follow the builder's order.

Greg's idea of keeping the source offset in `off` and the arena offset in
`next` for escaped strings was measured and not adopted: string access got
7-18 % slower with a select, and 3.5-18 % slower with a branch-free field
pick (Apple M-series, clang -O3), parsing was unchanged.

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

* Apply the review's wording fixes to the json_view documentation

- 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>

* Say that json_view converts integers while parsing

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

* Address the review: null inline nodes, trait spelling, and max() in json_view

- inline_nodes is null when the document has no inline nodes, instead of
  pointing past the end of the allocation; shrink_to_fit() no longer
  passes it to memcpy() for an empty node array
- is_byte_char and is_wide_char use conjunction/disjunction, which
  astyle leaves unspaced
- append_stream() uses (std::max) for the count read

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

* Include materialize.hpp in the view builder test

The test calls detail::view::materialize(), which only the single header
pulled in; the multiple-header build (JSON_TEST_USING_MULTIPLE_HEADERS)
failed with "'materialize' is not a member of detail::view".

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

* Rename emit() in the view builder for Qt compatibility

Qt defines emit as an empty macro, so a Qt header included before
json_view.hpp broke the declaration of the builder's emit(), see
issue #5865. It is now called push_node().

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

* Do not copy an empty run into an unallocated arena

memcpy() must not be passed a null pointer even for zero bytes, which
arena_run() did for an empty run while the arena was still empty
(ci_test_clang_sanitizer: "null pointer passed as argument 1" in
builder.hpp). Only the slow path can see such a run.

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

* Exclude the view builder test from Infer's reports

Infer's std::unique_ptr model confuses the values that the test's build()
helper returns by value and reports USE_AFTER_DELETE for one of them after
the destructor of an unrelated temporary (ci_infer, 12 reports, all in
tests/src/unit-json_view_builder.cpp). AddressSanitizer is clean on the
same tests.

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

* Skip the deleted-overload checks of json_view on MSVC 2015

MSVC 2015 does not treat selecting a deleted function in decltype as a
substitution failure, so is_detected reports the deleted
parse/parse_copy/accept/read(ptr, len) overloads as callable and the
static_asserts in "integer arguments do not compile" fail (AppVeyor
VS2015 jobs). Calling them still fails to compile there. Guard the
negative checks as unit-delete_deprecated_functions.cpp does.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-21 10:21:27 +02:00
Niels Lohmann a55cae45fd Test that the contiguous fast paths never read outside the input (#5826) 
* Test that the contiguous fast paths never read outside the input

The bulk string scanner, the SWAR searches, the UTF-8 prefix validator,
the 8-digit number loop, the 8-byte indentation skip, and the BSON/BON8
bulk string readers load several bytes at a time from contiguous input.
ASan misses over-reads into the slack of the same heap allocation, and
fuzzers rarely end an input exactly at a page boundary.

The new test copies each input directly in front of, and directly
behind, an inaccessible page (mmap/mprotect on POSIX,
VirtualAlloc/VirtualProtect on Windows), so reading even one byte
outside the input crashes. It covers the string-scan functions directly
and json::parse, accept, sax_parse (with and without comments) and all
binary readers through the public API, with inputs ending at every byte
of strings, escapes, UTF-8 sequences, numbers, literals, indentation
runs, and binary documents. Each result must match parsing the same
input from a std::string.

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

* Rename the reader parameter to avoid a flawfinder false positive

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

* Make the guard page test work without exceptions and under UBSan

Under JSON_NOEXCEPTION, the error paths abort instead of throwing, so the
outcomes are now computed with allow_exceptions=false there. Copying the
input with std::copy from char to unsigned char tripped Clang's implicit
conversion sanitizer; std::memcpy avoids the conversion.

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

* Test parse_float_native() at the guard page

parse_float_eisel_lemire() was removed by #5738, so the test no longer
compiled. The lexer converts floats from its token buffer, so the JSON
section never places a float token at the page boundary; the section now
calls parse_float_native() for float and double on every complete number
token directly and compares the result bit for bit with converting the
same token from a std::string.

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

* Fix clang-tidy findings in the guard-page tests

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

* Convert explicitly between bytes and characters in the guard-page tests

The clang sanitizer job (-fsanitize=integer, x86-64 where char is signed)
reported the implicit char -> unsigned char conversions of std::copy() into
the guarded buffer and of the std::string built from the binary inputs.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-20 22:24:09 +02:00
Niels Lohmann 4da932f518 Make parsing from std::istream and FILE* fast (#5828) 
* Make parsing from std::istream and FILE* fast

Squashed onto develop cd6b428ef (CI fixes from #5860). Original commits:

- Let the lexer's bulk fast paths run on a window of the input
- Scan the get area of an input stream in bulk
- Lock a FILE once per parse instead of once per character
- Add benchmarks for parsing from a FILE* and for many values from a stream
- Avoid implicit unsigned char to char conversion in stream tests
- Make file_input_adapter::unlock() safe to call on a moved-from adapter

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

* Add ABI tags for JSON_DISABLE_STREAM_BULK_SCAN and JSON_DISABLE_UNLOCKED_FILE_IO

Both macros select between two definitions of an input adapter, so
translation units compiled with different settings violated the ODR when
linked together. Like the other ABI-affecting macros, they now append a
tag to the inline namespace: _dsbs and _dufio. Their defaults move to
abi_macros.hpp so that json_fwd.hpp sees them, and the natvis file is
regenerated for the new namespaces.

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

* Skip the exception-only checks of the stream input tests without exceptions

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-19 22:00:58 +02:00
Niels Lohmann cc8334113c Do not use Qt's keyword macros as identifiers (#5866) 
* Do not use Qt's keyword macros as identifiers

The prefix tree used by unflatten() (#5836) had a member named slots, which
Qt defines as an empty macro, so including a Qt header before this library
failed to compile. Rename it to table and add a test that includes the
library with Qt's keyword macros (slots, signals, emit, foreach, forever)
defined.

Fixes #5865

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

* Keep the Qt keyword macros in the test from failing -Wunused-macros

Clang (-Werror) rejected the macros that the test defines but the library
must not use, and clang-tidy asked for parentheses around the arguments
of the Q_FOREACH imitation, where the variable is a declaration.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-19 22:00:31 +02:00
Niels Lohmann 0e95fe8200 Split the slowest Valgrind tests out of unit-large_json and unit-bjdata (#5862) 
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-17 08:28:28 +02:00
Niels Lohmann cd6b428ef0 Fix CI failures on develop from the API performance stack (#5860) 
Fixes every CI failure develop has had since the API performance stack (#5831-#5842) was merged: compiler warnings and errors (Clang, GCC 4.9/11, MSVC 2015/2017/2022), clang-tidy, cpplint, Cppcheck, IWYU, the examples check, the no-exceptions, diagnostic-positions, implicit-conversions and strict-NUL test configurations, and the MinGW link (now with LLD).

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-16 19:16:21 +02:00
Niels Lohmann 4da73dc5ff Fix compiler warnings on develop from the API performance stack (#5858) 
These PRs were merged while their CI runs were cancelled, so the warnings
went unnoticed. All of them fail the -Werror builds:

- json_pointer.hpp (#5836): size_t += int under GCC -Wsign-conversion
- binary_reader.hpp (#5839): char_int_type passed as char under GCC
  -Wconversion
- json.hpp (#5838): @throw without a description under clang
  -Wdocumentation
- string_escape.hpp (#5836): escape_into() was inserted between escape()
  and its documentation, so the @return was attached to a void function
- unit-diagnostics.cpp (#5832): clang -Wnrvo in a lambda without an
  explicit return type
- unit-to_json-rvalue.cpp (#5837): GCC -Wnoexcept (C++20) and clang
  -Wunneeded-member-function on the test type

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 22:42:46 +02:00
Niels Lohmann b41228c227 Fix AppVeyor failures from the Zmij double writer (#5843) 
MSVC 2015 warns C4554 on the shifts with casts in the fractional part
of zmij::to_shortest despite the parentheses; with /WX every target
fails to build. Name the shift amounts as constants instead.

The shortest-digits test built the candidates with one digit fewer via
a stream with std::setprecision(digits.size() - 2); the standard library
of MSVC 2017 ignores a precision of 0, so for two-digit values the
"shorter" candidates were the value itself. Truncate the digits
instead: the value lies within half a unit of the last digit, so the
truncated digits and their successor are the closest candidates.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:08:12 +02:00
Niels Lohmann dcb96e82fb Escape characters below 0x60 from a table straight into the write buffer (#5822) 
* Escape characters below 0x60 from a table straight into the write buffer

When the bulk scanner in dump_escaped_impl() stops at a control
character, a quote or a backslash, that byte used to go through the
UTF-8 decoder and a switch that wrote the escape byte by byte into
string_buffer, which was then copied into write_buffer at the next run.

A byte below 0x60 at a character boundary is a complete code point, so
it now skips the decoder: its escape sequence comes from a 96-entry
table of 8-byte rows (sequence padded with zeros, length in the last
byte), and all 8 bytes are copied straight into write_buffer with one
room check. The check sits inside the existing character-boundary
block, so it runs once per scanner stop and not once per byte; testing
every byte cost about 6% on twitter.json with ensure_ascii.

The switch in the decoder's accept branch lost its cases for
characters below 0x60, which can no longer reach it.

Output is byte-identical. The string-buffer boundary tests now use
\u-escaped non-ASCII characters, since simple escapes no longer reach
string_buffer, and a new test case checks every ASCII character at
every position against a reference escaper.

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

* Avoid raw string literals with backslashes in CHECK macros

MSVC's traditional preprocessor mis-lexes raw string literals inside
macro arguments and reports illegal escape sequences (C2017, C3850).

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

* Sweep invalid UTF-8 at every position through dump()

Compare dump() of strings with ill-formed UTF-8 (stray continuation
bytes, invalid lead bytes, overlong encodings, surrogates, code points
above U+10FFFF, and sequences cut short by ASCII, a quote, a backslash,
a lead byte, or the end of the string) with an independent reference
serializer, for every error handler and with ensure_ascii on and off.
The pattern is put at every position of short strings to cross the
strides of the bulk scanners, and of longer ones to cross the end of the
512-byte string buffer.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:08:10 +02:00
Niels Lohmann eb74fe2ab7 Fuzz the streaming input adapters against the contiguous one (#5827) 
* Fuzz the streaming input adapters against the contiguous one

The fast paths for contiguous input (bulk string scanning, multi-byte
loads, lazy position tracking) are taken only when parsing from a
pointer range; streams and non-contiguous iterators still read byte by
byte. The fuzzer drivers parsed only contiguous input, so a difference
between the two would ship unnoticed.

check_input_adapters() in fuzzer_common.hpp reads the input through a
std::istringstream, a std::list iterator range, and (on POSIX) a FILE*
from fmemopen, and asserts the same value, or the same exception id,
message and byte position, as for the pointer range. All seven drivers
call it; the JSON driver checks parse and accept, each with and without
ignore_comments. It replaces the stream check of the BON8 driver.

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

* Rename the reader parameter to avoid a flawfinder false positive

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:04:57 +02:00
Niels Lohmann ce28c722bc Allow the same type for number_integer_t and number_unsigned_t (#5815) 
* Allow the same type for number_integer_t and number_unsigned_t

basic_json did not compile with NumberUnsignedType == NumberIntegerType
because overloads on both types collided. Such a basic_json now stores
every integer as number_integer: the colliding overloads take a
placeholder type, unsigned C++ integers are converted to number_integer_t,
and value_t::number_unsigned maps to number_integer.

Also fixes two problems this configuration would hit: the unsigned
integer parser accepted values that wrap around to negative numbers, and
dump() overflowed when computing the absolute value of the minimum.

A repeated NumberFloatType gets a static_assert.

Refs #2573

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

* Use json::with_integers_t in the test and the docs

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

* ✅ skip patch test on GCC 5 to avoid internal compiler error

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

* Fix CI: name the unsigned overload type through template parameters

basic_json used number_unsigned_overload_t<basic_json> while the class was
still incomplete. MSVC rejected it as a recursive alias declaration and GCC
4.9, 5 and 7 crashed with an internal compiler error. basic_json now uses
number_unsigned_overload_type<NumberIntegerType, NumberUnsignedType>, which
also makes the GCC 5 workaround in the patch test unnecessary.

Infer reported a null dereference for the number_unsigned case in
from_json, which cannot happen for a basic_json whose number_unsigned_t is
number_integer_t; assert it.

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

* Address review: conjunction/negation trait, astyle-friendly alias, docs table order

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:04:42 +02:00
Niels Lohmann 6261d1e432 Construct the JSON Patch exceptions out of line (#5842) 
patch_inplace() built its error messages inline. In particular get_value()
concatenated the context-sensitive "operation 'x'" string on every call, even
when nothing was wrong. The patch exceptions now come from NEVER_INLINE
helpers: the index and key errors reuse basic_json's existing
throw_array_index_out_of_range/throw_key_not_found, and the seven
patch-specific messages get one helper each in detail/exceptions.hpp. Ids
and messages are unchanged, and unit-throw_messages pins them (with and
without JSON_DIAGNOSTICS).

citm_catalog patch: -6.6 % (Apple clang), -9.5 % (GCC 16).
The other remaining throw sites (parser::syntax_error, binary_writer,
serializer, input_adapters, enum_key_duplicate, format_error) were prototyped
and measured: no gain beyond noise, so they stay as they are.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:23 +02:00
Niels Lohmann 4f11512641 Speed up container destruction, iterator access and diff() (#5835) 
* Speed up container destruction, iterator access and diff()

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

* Destroy the first levels of a value by recursion

The pointer-reversing walk in destroy_container() avoids the call stack but
moves a value around for every container it visits. Recurse for the first
recursion_depth_limit() levels instead - no allocation, no thread-local, a
bounded frame - and hand anything deeper to the walk. Destroy twitter
0.49 -> 0.36 ms, citm 0.80 -> 0.74 ms (3.12.0: 0.47 / 1.00).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:22 +02:00
Niels Lohmann 6a27b9acb2 Construct remaining hot-path exceptions out of line so core functions inline (#5838) 
* Construct remaining hot-path exceptions out of line so core functions inline

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

* Move throw_key_not_found() before at_impl()'s comment block

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:22 +02:00
Niels Lohmann 91869983a0 Make the value lifecycle inline-friendly (#5840) 
* Make the value lifecycle inline-friendly

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

* Compare standard containers without a thread-local depth count

operator== on objects and arrays recursed through the containers' own
operator== and counted the depth in a thread-local variable. Where reading a
thread-local costs a call (macOS), that added about 10% to comparing documents
with many small containers. For the standard containers, walk objects and
arrays directly, compare scalars and strings inline, and pass the depth as an
argument, falling back to compare_iteratively beyond the depth limit. Other
container types keep the previous path.

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

* Address review: owns_memory() helper, leaf compare naming, astyle

- Add detail::owns_memory(value_t), a switch listing every enumerator so
  -Wswitch-enum flags it when a type is added; destroy() and the copy
  constructor use it instead of hand-written comparisons. Clang emits the
  same bitmask test as before.
- Drop the parentheses around the scalar operands in
  JSON_IMPLEMENT_SCALAR_CASES; they are only needed for the container
  operands (#1530), which the comment now says.
- Build equal_bounded_containers from detail::conjunction so astyle no
  longer pads the template brackets.
- Rename equal_scalar() to equal_leaf() and document why it also compares
  strings, unlike JSON_IMPLEMENT_SCALAR_FAST.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:21 +02:00
Niels Lohmann 4530d9681c Fix quadratic parent updates for ordered_json with JSON_DIAGNOSTICS (#5832) 
* Fix quadratic parent updates for ordered_json with JSON_DIAGNOSTICS

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

* Only trust containers known to keep their elements in place

Address review: decide whether an insertion may have moved the other
members by naming the containers that are known not to, instead of the
ones that are known to.

- detail::has_stable_elements: std::map, std::multimap,
  std::unordered_map and std::unordered_multimap; object_capacity()
  reports 0 for them.
- detail::is_nlohmann_ordered_map: only the real nlohmann::ordered_map
  (which only appends) reports its capacity().
- Any other object type reports unknown_size(), so it gets a full
  set_parents() on every insertion. Before, an object type without
  capacity() was treated as never moving, and one with capacity() (a
  sorted flat map, say) was trusted to move only on reallocation.
- set_parents_after_object_erase() re-parents unless the object type is
  stable; the unused set_parent() is removed.
- Comments say "the object type" instead of "ordered_json".
- New test with an object type that moves its members without changing
  its capacity; it fails without this change.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:21 +02:00
Niels Lohmann ca7740fef2 Move elements when converting rvalue containers to JSON (#5837) 
* Move elements when converting rvalue containers to JSON

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

* Simplify the rvalue to_json traits

Use negation<disjunction<...>> instead of a conjunction of negations and
keep the template argument lists compact (astyle only keeps the spaced
'< ... >' form when it is written that way).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:20 +02:00
Niels Lohmann 6ba53e63dd Speed up array-to-container from_json (#5833) 
* Speed up array-to-container from_json

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

* Hint the end when converting an object to a standard container

from_json for map-like containers called emplace() without a hint, which
searches the tree for every key. The keys of the source object are sorted, so
inserting with the end as the hint is constant time, as it was in 3.12.0 via
std::inserter. get<std::map<...>>() of a 25,000 entry object: 4.2 ms -> 3.25 ms
(3.12.0: 3.7 ms).

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

* Fall back to emplace() in object from_json for containers without emplace_hint()

ordered_map has no hinted insert, so the insert(end(), ...) call broke
from_json into types holding an ordered_map (regression test #5122).
Use emplace_hint() where available and plain emplace() otherwise.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:20 +02:00
Niels Lohmann 0a4b3a84ee Speed up JSON pointer parsing, formatting, comparison and lookup (#5836) 
* Speed up JSON pointer parsing, formatting, comparison and lookup

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

* Restore unflatten() speed after the linear-time rewrite

The prefix tree introduced for linear unflatten() kept a std::map per prefix,
copied each token into it and looked every token up a second time while
creating the values. Replace the per-prefix maps by one open-addressing table
keyed by (parent, token) that refers to the parsed tokens, skip the lookups for
the prefix shared with the previous key (flattened objects are mostly sorted),
and derive the prefix numbers of the second pass from parent links instead of
lookups.

Time and memory stay linear in the pointer depth, and the result is still
independent of the iteration order of the flattened object.

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

* Put [[noreturn]] before __attribute__ on the JSON pointer throw helpers

Clang 18 on Linux rejects a C++11 attribute list after a GNU
__attribute__ ("an attribute list cannot appear here").

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:20 +02:00
Niels Lohmann 0c4e7c103c Make flatten() linear for ordered_json (#5834) 
* Make flatten() linear for ordered_json

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

* Use priority_tag instead of a C-style variadic overload in add_flattened

clang-tidy flags the ellipsis fallback (cert-dcl50-cpp,
modernize-avoid-variadic-functions).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-15 20:01:19 +02:00
Niels Lohmann 1c92a3c5de Update Google Benchmark to 1.10.0 (#5823) 
* Update Google Benchmark to 1.10.0

Bump the pinned release and its archive checksum. Reword the comment and
README: the version is fixed for reproducible builds and updated like any
other dependency; results stay comparable because both sides of a
comparison are built with the same version.

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

* Do not name the Google Benchmark version in the README

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-14 17:39:16 +02:00
Niels Lohmann 91a7a94cc6 Write doubles with the shortest digits (Żmij), digits in registers (#5634) 
* Write doubles with the shortest digits (Żmij), digits in registers

Write doubles with the conversion of Zmij by Victor Zverovich (MIT),
ported to C++11 (detail/conversions/zmij.hpp). It finds the
shortest decimal that reads back as the same double, and the
closest one if there are several. Grisu2, used until now, is fast
but not always shortest: it sometimes writes a 17th digit where 16
suffice, or a last digit that is not the closest. The layout is
unchanged (1.5, 100.0, 1e+100, -0.0); float keeps Grisu2.

Digits are converted eight at a time with the BCD conversion of
Xiang JunBo, as in Zmij, and written with one byte swap per eight
digits and fixed-size moves instead of per-digit loops. Leading and
trailing zeros are counted from those bytes. to_chars() uses a
local buffer when the caller's is shorter than the 41 bytes this
may write. The powers of ten come from the number-parsing table,
adjusted where it holds values rounded up, and extended with Zmij's
compressed tables beyond 10^308.

write_shortest() converts its 16 digits in one vector register
(SSE2 on x86-64, NEON on 64-bit Arm, both baseline) and inserts the
decimal point inside the register, avoiding a store-forwarding
stall that cost about 25% of the time to write a double. dump()
writes floats and integers straight into the serializer's write
buffer instead of copying them from a member buffer, and small
integers eight digits at a time. read_eight_bytes() and
parse_eight_digits() are marked always-inline, which GCC had been
calling out of line in the number-parsing loops.

Of one million random doubles, about 0.14% are now written with
different digits, always to a value that still reads back as the
same double.

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

* Fix CI findings in the Zmij writer and its tests

- bit_ops.hpp: include macro_scope.hpp (JSON_HEDLEY_ALWAYS_INLINE); fixes IWYU
- to_chars.hpp: C4100 for the unused parameter in release builds, clang-tidy
  sign comparison, cpplint runtime/int, GCC -Wstrict-overflow (unsigned abs)
- unit-to_chars.cpp: parse with the library instead of strtod (MinGW's strtod
  rounds some 16/17 digit inputs wrongly); no floating-point std::to_chars
  with icpc

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

* Select the Zmij conversion by a trait, not by the double overload

The non-template overloads for double asserted binary64 doubles wherever json.hpp was included, so the library no longer compiled where double is not IEEE 754 binary64 (AVR, -fshort-double). A trait now picks Zmij for any binary64 type, including a long double of that format (MSVC, Apple Arm), and Grisu2 for the others. Remove the unused write_short_decimal, powers_of_ten_16, zmij::decimal, zmij::to_decimal, and shortest_digits(double).

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

* Credit Zmij's authors in to_chars.hpp, the README, and the license page

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

* Silence MSVC C4127 for a platform-constant check in the to_chars test

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

* Regenerate the amalgamated headers

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-14 17:38:37 +02:00
Niels Lohmann 5b4c8f9b00 Speed up the lexer: own float parser, string scan, and \u table (#5738) 
* Speed up the lexer: own float parser, string scan, and \u table

Give the library its own correctly rounded float converter for
binary32 and binary64 (IEEE 754), and speed up the lexer's string
and escape scanning.

The converter splits a number token into sign, significand, and
decimal exponent, then tries Clinger's fast path, then a templated
Eisel-Lemire step, and falls back to an exact big-integer digit
comparison for tokens with more than 19 significant digits whose two
candidate values round differently. This replaces std::from_chars
and strtod/strtof for both formats, so parsed values no longer
depend on the C/C++ library or the current locale. The strtold
fallback kept for other long double formats (x87, binary128) now
also copies a multi-byte decimal point correctly, fixing #5660.
eisel_lemire() and decimal_to_float() are always inlined so callers
keep the whole conversion in their hot loop.

The string-scanning kernels in string_scan.hpp find a stop byte with
the trailing-zero count of the SWAR mask instead of a byte loop, and
scalar_string_bulk_run() validates a run of multi-byte UTF-8
sequences one after another instead of re-searching after each one.

get_codepoint() decodes a contiguous \uXXXX escape with one table
lookup per byte instead of four range-checked get() calls; the
streaming path and all error positions are unchanged.

Adds 508 generated hard float-parsing cases with expected binary32
and binary64 bits, and kernel-comparison tests for the string scans
and the escape table against byte-by-byte references.

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

* Fix CI warnings in own float parser

- pow5_table.hpp: pow5_128_largest_power was unused in this branch's
  own code (GCC -Werror=unused-const-variable); tie it to the table
  size with a static_assert instead of removing it, since a later
  branch in the stack (json-view/23-zmij) uses it.
- number_parse.hpp: rename the local variable `copy` to `buffer` to
  satisfy cpplint's build/include_what_you_use check.
- unit-class_lexer.cpp: extend the NOLINT list on the seeded mt19937
  with bugprone-random-generator-seed, and parenthesize
  `8 * sizeof(Bits) - 1` for clang-tidy.

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

* Load string scan words with memcpy and use MSVC bit-scan intrinsics

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

* Reword float conversion notes for the string type and number_float_t docs

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

* Fix clang-tidy 22 findings in unit-class_lexer.cpp

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

* Mark the unsigned long of the MSVC bit scans for cpplint

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

* Regenerate the amalgamated headers

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

* Drop the position updates in the bulk \u path, which #5809 made unused

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

* Address review: std::any_of in has_nonzero_digit, comment punctuation

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

* Use data() instead of c_str() in the multi-byte decimal point path

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-14 17:38:36 +02:00
Niels Lohmann e839bbd1c0 Export client-facing headers from json.hpp for IWYU / include-cleaner, and check clients in CI (#5813) 
* Mark json_fwd.hpp as exported by json.hpp for IWYU / include-cleaner

json_fwd.hpp is the only header declaring the nlohmann::json alias, so
include-what-you-use and clang-tidy's misc-include-cleaner attributed
the name to it and told users of <nlohmann/json.hpp> to include
json_fwd.hpp as well (or instead, which breaks compilation).

Fixes #5812

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

* Export the remaining client-facing headers from json.hpp and check clients with IWYU

Besides json_fwd.hpp, include analyzers also told clients of
<nlohmann/json.hpp> to include detail/json_ref.hpp (brace
initialization), json_literals.hpp (_json, _json_pointer),
adl_serializer.hpp, detail/macro_scope.hpp (NLOHMANN_DEFINE_*) and
detail/abi_macros.hpp. Mark those includes as exported, too.

ci_single_binaries only checked each header on its own, so it could not
notice this. It now also runs IWYU and clang-tidy's misc-include-cleaner
on small client programs in tests/iwyu_consumer, which fail on develop.
With the exports, json_literals.hpp no longer gets the json_fwd.hpp
suggestion that kept it out of the IWYU gate, so it is gated again.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-13 17:17:15 +02:00
Niels Lohmann aa9620fb15 Skip the indentation after a newline 8 bytes at a time (#5810) 
Pretty-printed JSON indents every line with a run of spaces, which
skip_whitespace() read one character at a time. For contiguous input
(bulk_scan) the lexer now skips the spaces after a newline 8 bytes at a
time directly in the input buffer, including the leading spaces of the
last, partial word. This bypasses get(), which is safe because
bulk_scan implies the lazy position from the previous commit: nothing
is counted per character.

Compared to lazy positions alone, pretty-printed input (twitter,
citm_catalog with indent 2 and 4) parses up to 13% faster and accept()
gets up to 30% faster (GCC 13 and clang 18 on x86-64, Apple clang 21 on
arm64). Minified input is unchanged within noise.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-13 17:16:52 +02:00
Niels Lohmann f23830b65e Derive the lexer position lazily for seekable input (#5809) 
* Derive the lexer position lazily for seekable input

The lexer counted the read position on every character: two increments
and a newline check per get(), all on members kept in memory. For
seekable input (pointers, strings, other random-access byte ranges) the
position can be derived instead: chars_read_total is the adapter's read
count (including reads at EOF) minus a pending unget, and line and
column are recomputed from the consumed input only when get_position()
is called, i.e. on parse errors. JSON_DIAGNOSTIC_POSITIONS uses the new
O(1) get_chars_read_total(). Stream, file, wide-string and user-defined
adapters keep the eager counters.

Parsing pretty-printed input gets 8-12% faster and accept() 12-27%
(canada, citm_catalog, twitter; clang 21 arm64 and GCC 13 x86-64).
Error messages, byte offsets, SAX positions and diagnostic positions are
unchanged (differential comparison against develop on 548k inputs).

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

* Move the std::vector<std::byte> binary type tests out of unit-regression3

The #4804/#4209 tests instantiated a second basic_json specialization
(with_binary_t<std::vector<std::byte>>), including its parser and CBOR
reader. With clang 18, the C++20 object of unit-regression3.cpp had
32656 COFF sections on develop; the lazy position helpers pushed it to
32975, past what the MinGW linker of the Windows clang jobs handles
("relocation truncated to fit: IMAGE_REL_AMD64_REL32 against .rdata").
unit-custom-binary-type.cpp already instantiates the same type, so the
tests move there; unit-regression3.cpp drops to 27616 sections.

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

* Report the parse errors of the position test via SAX

The test caught json::parse_error, so it aborted in the
ci_test_noexceptions build, where JSON_NOEXCEPTION turns the throw into
std::abort(). sax_parse() hands the error position and the exception
object to parse_error() without throwing, so the test now records them
there and runs in every configuration.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-13 17:16:52 +02:00
satelliteprogrammer 40a62947d3 support JSON Merge Patch (RFC 7396) diff creation (#4965) 
* support JSON Merge Patch (RFC 7396) diff creation

The JSON merge patch document format describes the set of modifications
to a resource's content, that more closely mimics the syntax of the
resource being modified.

However, and in contrast to JSON Patch (RFC 6902), a JSON Merge Patch
cannot express certain modifications, e.g., changing an array element
at a specific index, or setting a specific object value to null.
The null value in a JSON Merge Patch is used to remove the key from the
object.

The diff algorithm is not part of the RFC 7396, but it was tested
against all examples provided, plus additional cases on how null values
are handled.

Signed-off-by: Luís Murta <luis@murta.dev>

* improve algorithm efficiency

Signed-off-by: Luís Murta <luis@murta.dev>

* fix inconsistent nulls and empty arrays

Also add CHECKs for the patch, documentation and run `make amalgamate`.

Signed-off-by: Luís Murta <luis@murta.dev>

* documentation cleanups

Signed-off-by: Luís Murta <luis@murta.dev>

* add an iterative fallback to merge_diff

Bound the recursion depth like diff() and merge_patch(), and test values
nested past the bound.

Signed-off-by: Luís Murta <luis@murta.dev>

* address the remaining review comments

Signed-off-by: Luís Murta <luis@murta.dev>

* move multi-line raw strings out of CHECK macros

GCC 4.8/5, ICPC and NVHPC mis-tokenize multi-line raw string literals
inside macro arguments, breaking the build or the parsed JSON.

Signed-off-by: Luís Murta <luis@murta.dev>

---------

Signed-off-by: Luís Murta <luis@murta.dev>
 2026-10-12 09:33:43 +02:00
Niels Lohmann c59ad95252 Expect type_error.321 for deep discarded values in the BON8 writer test (#5807) 
#5806 added the test while #5802 made to_bon8 reject discarded values; both
merged, so the test failed on develop.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-11 10:27:16 +02:00
Niels LohmannandClaude Opus 5.5 b38a2c9177 Stop the BON8 writer overflowing the stack on deep values (#5806) 
* Stop the BON8 writer overflowing the stack on deep values

to_bon8() recursed once per nesting level, so a value the iterative
BON8 reader accepts (e.g. ~24k nested one-element arrays) crashed on
the way back out. #5781 bounded the CBOR, MessagePack, and UBJSON/BJData
writers, but BON8 was merged before it and was not covered.

Apply the same scheme: recurse for the first recursion_depth_limit()
levels, then finish the value with write_bon8_iterative, which keeps
the open containers on a heap stack (reusing binary_container_frame)
and writes the 0xFE closer when it leaves a container with more than
four elements. The output is byte-for-byte unchanged.

Fixes https://issues.oss-fuzz.com/issues/572238015

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

* Merge the array and object branches of the BON8 iterative writer

write_bon8_iterative and write_bon8_value_or_push handled arrays and
objects in separate branches that repeated the end-of-container check,
the 0xFE closer and the marker computation. Share those parts and branch
only where arrays and objects really differ. The output is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Hz7VJi1FTKr6gpseLErbbS
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
 2026-10-11 08:24:35 +02:00
Niels Lohmann eb8899a29c Restore v3.12.0 support for custom object key types (#5795) 
* Restore v3.12.0 support for custom object key types

Custom object_t types whose key_type is not string_t compiled with
v3.12.0 for several APIs that unreleased changes broke:

- to_bson failed for every custom key type (#5553 kept a const string_t*
  to the key); the nested entry's header is now written where the entry
  is found.
- Copying deep values (and parse, merge_patch, update, insert) required
  operator== on keys (#5389); keys without one are now paired via find().
- to_cbor/to_msgpack required an implicit conversion to string_t (#5746,
  #5328); keys without one go through a temporary basic_json again.
- at() required a conversion to string_t for its error message (#5727);
  other keys are passed to concat() unchanged again.

The new unit-custom-object-key-type.cpp covers five key types with
different capabilities.

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

* Use the with_object_t alias for the custom object key test types

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

* Avoid floating-point equality in custom key type test

GCC with -Werror=float-equal rejects comparing the double value with ==.

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

* Write the head of nested BSON elements in one helper

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

* Suppress bugprone-return-const-ref-from-parameter in key_for_message

The reference is only passed to concat() within the full-expression that
holds the key, like the similar helpers in binary_writer.hpp.

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

* Make the value of the custom test key types private

clang-tidy (cppcoreguidelines-non-private-member-variables-in-classes)
rejects the protected member; the derived key types use a protected
accessor instead.

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

* Pass keys with data() and size() unchanged into the at() miss message

key_for_message() converted every key that string_t can be constructed
from, so a miss on a string_t or string_view key copied it before
concat() copied it again. Keys that concat() can append through data()
and size() are now passed through; only other keys (string literals,
key types that just convert to string_t) are converted.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-11 08:24:31 +02:00
Niels Lohmann 74a03dec84 Throw type_error.321 for discarded values in to_bon8 (#5802) 
write_bon8_value silently skipped discarded values, but the array/object
count marker still counted them, so [1, discarded] produced 82 91: a marker
announcing two elements followed by one. Throw type_error.321 like the other
binary writers do, at any nesting level.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-11 08:22:00 +02:00
Niels Lohmann 2cca04ae6f Report one-character non-numeric array indices like longer ones (#5800) 
* Report one-character non-numeric array indices like longer ones

A JSON pointer reference token that is not a number but has only one
character (e.g. "/a/x") was reported as out_of_range.404 ("unresolved
reference token"), because the "is not a number" check only ran for
tokens longer than one character; "/a/xy" got parse_error.109. Both now
throw parse_error.109. "-" and the empty token are still reported as
out_of_range.404. As a consequence, value(json_pointer, default) on an
array now throws for "/x" as it already did for "/xy".

Also document why ordered_map::erase's destroy/placement-new loop on
pair<const Key, T> is kept despite [basic.life]/8 before C++20.

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

* Document the one-character array index change

Add 3.13.0 version-history entries to at, operator[], value, patch,
patch_inplace, and unflatten, and describe in exceptions.md which array
indices throw parse_error.109 and which out_of_range.404.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-11 08:21:41 +02:00
Niels Lohmann 1649d9eda4 Use and extend the detail helpers to remove duplicated code (#5783) 
* Use and extend the detail helpers to remove duplicated code

Library:
- binary_reader: format bytes with hex_byte() instead of snprintf
- add throw_type_must_be() for the 20 copies of type_error.302
- binary_reader: add last_byte_error()/unexpected_byte() for the 32
  "parse error at the last read byte" sites (replaces bon8_error)
- json_sax: add check_container_size() for out_of_range.408 and
  diagnostic_positions::set_container_start/_end()
- json_pointer: add throw_no_parent() (405) and throw_unresolved() (404)

Tests:
- unit-class_parser uses the shared utils::SaxCountdown
- move SaxEventLogger (and its ExitAfter* variants) from unit-class_parser
  and unit-deserialization into the new tests/src/test_sax.hpp

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

* Factor out more repeated error paths and test boilerplate

Library:
- add throw_cannot_use_with() for the 34 copies of type_error.304-312
  "cannot use X with Y"
- iter_impl: add throw_cannot_get_value() (invalid_iterator.214)
- parser: add syntax_error() for the 12 parse_error.101 sites
- ordered_map: share the four at() bodies via at_impl()
- json_sax_dom_callback_parser: add pop_container() for end_object()
  and end_array()
- binary_reader: build the two UBJSON/BJData length-type messages with
  concat() and last_byte_error()

Tests:
- move same_value(), the NDEBUG guard, and step 0 (parse without
  exceptions) of the seven fuzzer drivers into tests/src/fuzzer_common.hpp

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

* Name the exception ids and address review comments

Add detail::exception_id, a scoped enum with one named enumerator per
documented exception id, and use it for every id in the library. The
create() functions get an overload for it; the int overloads stay for
user code.

Following the review of #5783: add binary_reader::invalid_byte() and
length_type_error(), basic_json::throw_subscript_wrong_type(), move the
fuzzer includes and the using-declaration into fuzzer_common.hpp, and
rename test_sax.hpp to sax_event_loggers.hpp.

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

* Silence -Wweak-vtables for the SAX event loggers

The loggers moved from anonymous namespaces in the test files into
sax_event_loggers.hpp, so clang now warns that their vtables are
emitted in every translation unit.

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

* Silence MSVC 2015 C4100 in parser::syntax_error for static SAX::parse_error

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

* Inline invalid_byte() into its call sites

The wrapper only fixed the message string of unexpected_byte(), which is
the same kind of per-argument helper that was declined for
throw_type_must_be(). Call unexpected_byte("invalid byte", ...) directly.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-11 08:21:13 +02:00
Niels Lohmann 74aefc3486 Move custom object key tests out of unit-cbor.cpp and unit-msgpack.cpp (#5798) 
The custom object key tests from #5328 instantiate a second basic_json
specialization in unit-cbor.cpp and unit-msgpack.cpp. This pushed
unit-msgpack.cpp.obj past 65535 sections in the clang (MinGW) jobs of
the Windows workflow, and linking test-msgpack_cpp11 fails with
"relocation truncated to fit: IMAGE_REL_AMD64_REL32 against `.rdata'".

The GNU linker keeps the section an associative COMDAT section belongs
to in 16 bits (x_associated in include/coff/internal.h), although big
object files store 32 bits. In larger objects it therefore ties the
jump tables of inline functions to the wrong function and discards them
together with that function's duplicate.

Move the four tests unchanged into unit-custom-object-key-type.cpp and
document the limit in windows.yml.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-10 00:05:02 +02:00
Niels Lohmann 2913e96433 Unflatten in time and memory linear in the pointer depth (#5793) 
* Unflatten in time and memory linear in the pointer depth

#5443 made unflatten() decide between arrays and objects independently
of the iteration order by collecting the pointer prefixes that have a
reference token 0 below them in a std::set<std::vector<string_t>>.
Every such prefix was stored as a copy of all its reference tokens, and
get_and_create() compared whole prefix vectors at every step, so
unflattening a pointer of depth d took time and memory quadratic in d:
a 10,000-level array pointer took 18 s and 1.3 GB, a 100,000-level one
did not finish.

The prefixes are now numbered nodes of a tree, so each is stored once
and get_and_create() follows the tree token by token. The result is
unchanged, including its independence of the iteration order.

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

* Initialize prefix_tree members to satisfy -Weffc++

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

* Move prefix_tree setup and child insertion into member functions

The constructor now creates the root node, add_child() inserts a
reference token below a prefix and returns the child's number, and
find_child() looks one up for get_and_create().

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-09 17:57:31 +02:00
Niels Lohmann 44e8597701 Flatten deeply nested values without recursing per nesting level (#5792) 
* Flatten deeply nested values without recursing per nesting level

json_pointer::flatten() called itself once per nesting level, so
flatten() on a value nested deeply enough exhausted the call stack.
#5547 and #5548 fixed merge_patch() and diff() from #5393, but flatten()
was left out.

flatten() now walks the value with an explicit stack and keeps the path
in one buffer that grows and shrinks with it. It has a single code path
and no depth limit: the old version built a new path string per child,
so the iterative one is no slower on shallow values and much faster on
deep ones. The output, including the order of an ordered_json result,
is unchanged.

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

* Construct flatten frames in place

Give the frame a constructor so both call sites can use emplace_back, as
suggested in the review; index starts at 0 for every frame.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-09 17:06:41 +02:00
Niels Lohmann 374dfe4f0f Keep converted object keys alive while writing UBJSON and BJData (#5791) 
* Keep converted object keys alive while writing UBJSON and BJData

Since #5746, write_ubjson and write_ubjson_iterative pass each object key
to sanitize_utf8_for_write and keep the returned reference. When
object_t::key_type is not string_t but converts to it, the argument is a
temporary that is destroyed at the end of the statement, and the
function returns a reference to it in every case but a sanitized copy,
so the key bytes are read from a dead object (AddressSanitizer:
stack-use-after-scope). Default json and ordered_json are unaffected.

Bind the key to a named object_key_string_t first: a reference when
key_type is string_t, so no copy is added there, and a converted copy
otherwise. A deleted overload of sanitize_utf8_for_write for anything
other than string_t turns a recurrence into a compile error.

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

* Suppress -Wunused-member-function for the converting_key test type

converting_key::data() is only called when JSON_DIAGNOSTICS is enabled.

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

* Fix clang-tidy findings in the UBJSON/BJData converted-key fix

Suppress hicpp/modernize-use-equals-delete on the deleted
sanitize_utf8_for_write overload: it guards a private helper and must stay
private. Replace the C-style array in the new test with std::array.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-09 17:05:36 +02:00
Niels Lohmann d540750f21 Use the with_*_t aliases in the remaining tests and docs (#5790) 
#5787 missed the instantiations spelled as `basic_json <` (astyle's
formatting) or ending in the CustomBaseClass argument. Convert them,
including the binary_t.md example pointed out in review.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-09 16:56:14 +02:00
Alex Prabhat Bara 69a0c1b82c Avoid allocating temporary basic_json for cbor and msgpack object keys (#5328) 
* avoid allocating temporary basic_json for CBOR and MessagePack object keys

Signed-off-by: alexprabhat99 <alexpbara@gmail.com>

* add size() to the custom object key test type

UBJSON and BJData access object keys through size() and c_str()
directly, so the key type now provides both and the comment says why.

Signed-off-by: alexprabhat99 <alexpbara@gmail.com>

* address review: drop key size()/c_str(), test keys below the depth limit

Nothing in the library calls size() or c_str() on an object key, so the
test key type only keeps data(), which JSON_DIAGNOSTICS needs.

The CBOR and MessagePack custom key tests now also nest objects deeper
than detail::recursion_depth_limit(), so keys written by
write_cbor_iterative and write_msgpack_iterative are covered as well.

Signed-off-by: alexprabhat99 <alexpbara@gmail.com>

---------

Signed-off-by: alexprabhat99 <alexpbara@gmail.com>
 2026-10-09 13:22:07 +02:00
Niels Lohmann d33068da73 Address review comments on the API stability docs and a test comment (#5784) 
* Address review comments on #5775 and #5779

Allow new defaulted parameters and new default arguments in the API
stability rules, mention the macro opt-in, and drop the redundant
recompile advice. Describe test-diagnostics-optimized as the regression
test for the fixed #5742.

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

* Document what counts as a breaking change in the API stability rules

Spell out the 3.x compatibility rules in the roadmap: new defaulted
parameters, new default arguments, noexcept/constexpr, template
parameters, parse and dump results, accepted input, key iteration order,
iterator invalidation, implicit conversions, to_json/from_json lookup,
json_sax, value_t enumerators, and documented macros, CMake options and
headers. Also list std::hash values as not part of the public API, and
link the macro overview from the section.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-08 17:44:34 +02:00
Niels Lohmann 3d7f554927 Use the with_*_t aliases in tests, examples, and docs (#5787) 
* Use the with_*_t aliases in tests, examples, and docs

Replace spelled-out basic_json<...> instantiations that only change one
or two template parameters with nlohmann::json::with_*_t (or
ordered_json::with_*_t when the object type is ordered_map). Types that
change all three number types chain with_integers_t and with_float_t.

The raw basic_json<...> spelling stays where the template parameter
list itself is the subject: the alias tests in unit-udt.cpp, explicit
instantiations, and the ordered_json/compile-time docs.

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

* Fix unit-large_json for clang and JSON_DIAGNOSTICS

Two test problems from #5781 broke CI on develop: CAPTURE(depth); trips
clang's -Wextra-semi-stmt, and the type_error.321 messages did not
account for the diagnostics path prefix.

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

* Use static_cast in unit-hash for clang-tidy

#5772 added functional casts that clang-tidy reports as C-style casts
(google-readability-casting). Also append a char instead of a
one-character string in unit-large_json.

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

* Declare the expected message prefix const in unit-large_json

Without JSON_DIAGNOSTICS the prefix was never modified, which
clang-tidy reports (misc-const-correctness).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-08 16:11:16 +02:00
Suyog Verma a269794db7 Use MSVC intrinsics for full multiplication (#5782) 
* Use MSVC intrinsics for full multiplication

Signed-off-by: Suyog Verma <suyogverma0057@gmail.com>

* Fix formatting in unit-class_lexer

Signed-off-by: Suyog Verma <suyogverma0057@gmail.com>

* Address review feedback

Signed-off-by: Suyog Verma <suyogverma0057@gmail.com>

---------

Signed-off-by: Suyog Verma <suyogverma0057@gmail.com>
 2026-10-08 08:49:32 +02:00
Niels LohmannandAfonso Januário a5f5d3059b Make std::hash<basic_json> consistent with operator== for numbers (#5772) 
* Make std::hash<basic_json> consistent with operator== for numbers

operator== converts between number_integer, number_unsigned, and
number_float before comparing, so json(0), json(0U), and json(0.0)
all compare equal. hash() folded the specific value_t into the
result for each of the three numeric cases, giving each a distinct
hash and breaking the standard Hash requirement that a == b implies
hash(a) == hash(b). A std::unordered_set could therefore hold all
three as separate elements even though they compare equal.

hash() now treats all three numeric variants the same way: it
converts the value to number_float_t and combines it with a single
shared type tag, so any two numbers operator== considers equal hash
identically regardless of which internal type actually holds them.

Updated the accompanying test to check this consistency directly
(including via an actual unordered_set) instead of asserting that 0,
0U, and 0.0 hash differently, since that assumption was the bug.
Also corrected the function's own doc comment and the std::hash API
docs, which described the old behavior as intended.

Fixes #5400

Signed-off-by: Afonso Januário <afonso-januario@hotmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Remove now-unused number_integer_t/number_unsigned_t typedefs in hash()

Merging the three numeric branches into one that only reads
number_float_t left these two aliases unused, which several CI
configurations treat as a build error under -Wunused-local-typedefs.

Signed-off-by: Afonso Januário <afonso-januario@hotmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Mark the unordered_set in the hash regression test const

clang-tidy's misc-const-correctness check flagged it: the set is
never mutated after construction, only read via size().

Signed-off-by: Afonso Januário <afonso-januario@hotmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Normalize -0.0 in number hashes and test range ends

operator== compares numbers exactly since #5459, so equal numbers
share one value and convert to the same number_float_t. Update the
comment accordingly, map -0.0 to 0.0 before hashing (std::hash need
not do that), and test -0.0 and the ends of the integer ranges. Show
hash(0.0) in the docs example and note the change in the version
history.

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

* Clarify hash documentation after review

- Say "may hash differently" for null, false, and numbers, since a
  collision across types is possible.
- Name the storage types (signed integer, unsigned integer,
  floating-point number) instead of example literals.
- Explain that the hash survives converting an integer to
  number_float_t but not the lossy conversion back, and that unequal
  numbers may share a hash.
- State that the example hash values are illustrative only and vary by
  platform, compiler, compiler version, and library version.

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

---------

Signed-off-by: Afonso Januário <afonso-januario@hotmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Afonso Januário <afonso-januario@hotmail.com>
 2026-10-07 19:18:51 +02:00
Niels Lohmannayush-singh-0601ayush-singh-0601
 		43fe8928e1 Stop binary writers overflowing the stack on deep values (#5781) 
* Stop binary writers overflowing the stack on deep values

to_cbor, to_msgpack, and to_ubjson recurse once per nesting level.
The parser is iterative, so a value the library accepts can crash on
the way back out.

Keep the existing recursive path for the first 128 levels and finish
anything deeper on a heap stack. Output is unchanged. BSON is left
alone because its extra size walk is a separate change.

Rebased onto the value-type output sink. The heap frames now initialize
every member, which is what -Weffc++ was rejecting.

See #5392.

Signed-off-by: ayush-singh-0601 <singhayush062006@gmail.com>
(cherry picked from commit cf65ac438f)
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Redesign the iterative binary writers around a shared recursion depth limit

Address the open review on the non-recursive CBOR/MessagePack/UBJSON/BJData
writers (#5518):

- Delete the CBOR array/object prefix helpers; both the recursive and
  iterative paths call write_cbor_head(), which already existed on develop.
- MessagePack: share one write_msgpack_array_prefix()/write_msgpack_object_prefix()
  helper per container kind between the recursive and iterative paths, both
  going through to_msgpack_length() so an over-long container throws
  out_of_range.412 identically either way.
- Reuse detail::recursion_depth_limit() instead of a separate constant, the
  same bound serializer::dump() and write_bson_document() already use.
- Redesign the frames after bson_frame/dump_frame: only a container with
  elements is ever pushed, its header is written at the point it is pushed,
  and the iterator is set in the frame's constructor instead of a
  default-then-assign two-step with a since-removed "started" flag. The
  UBJSON frame keeps only the value pointer, the per-element prefix_required
  flag, and the iterator; write_closer and is_object are no longer stored,
  since the former is always !use_count (use_count is constant for the whole
  document) and the latter follows from value->is_object().
- Factor the BJData ND-array shape check into is_bjdata_ndarray(), used by
  both the recursive object case and the iterative pushing logic.
- Give the frame classes the GCC -Weffc++ treatment already used for
  diff_frame: a noexcept converting constructor plus the five special members
  defaulted with no explicit noexcept.
- Fix two @ref self-references in write_cbor/write_msgpack/write_ubjson's own
  doc comments to point at the public to_cbor/to_msgpack/to_ubjson/to_bjdata
  API instead.
- The iterative object-key write for CBOR/MessagePack now runs the same
  strict-mode check_utf8() against the parent object as diagnostics context
  that the recursive path already ran, so the two paths raise identical
  diagnostics across the switch-over.
- Rewrite the tests: round trips instead of a bare size check, byte-exact
  comparisons against the recursive output at depths around the bound, a
  deep object and a BJData ND-array past the bound, a deep discarded value
  (type_error.321), and the OSS-Fuzz 566583014 CBOR/MessagePack regression.

BSON is unaffected by this change; it already walks its documents
iteratively and is covered separately by #5553.

Co-authored-by: ayush-singh-0601 <179524189+ayush-singh-0601@users.noreply.github.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: ayush-singh-0601 <singhayush062006@gmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: ayush-singh-0601 <singhayush062006@gmail.com>
Co-authored-by: ayush-singh-0601 <179524189+ayush-singh-0601@users.noreply.github.com>
 2026-10-07 19:18:20 +02:00
Niels Lohmann 3c465beb61 Add tests for error_handler_t::keep in dump() (#4555) 
Squashed onto develop from:
- Add error_handler_t::keep to copy invalid UTF-8 bytes unchanged
- Mention error_handler_t::keep in the README

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-07 19:17:57 +02:00
Niels Lohmann 069ace74af Round-trip BJData ND-array annotations exactly (single precision, key order) (#5707) 
Squashed onto develop from:
- Round-trip BJData ND-array annotations exactly (single precision, key order)

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-07 19:17:18 +02:00
Niels Lohmann 367336c83d Fix CI on develop after #5585 (#5779) 
* Fix CI on develop after #5585

- test-diagnostics-optimized: -O3 makes GCC's -Winline and
  -Wsuggest-attribute=pure/const warnings fire with the ci_test_gcc flag
  set; turn them off for this test.
- test-diagnostics-optimized: suppress Clang's -Wexit-time-destructors for
  the static table in to_json.
- Infer: raise pulse-max-disjuncts from 20 to 40. With the default,
  Pulse loses the stored type in basic_json::replace_value() and reports
  false null dereferences of get_ptr() results in unit-pointer_access.cpp.

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

* Ignore Infer's false USE_AFTER_DELETE in ordered_map::erase

Infer's std::string model keeps the buffer of a moved-from string, so the
destroy-and-reconstruct loop in erase(first, last) looks like it destroys a
buffer twice.

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

* Mark throw_on_discarded()'s parameters as used without exceptions

With JSON_NOEXCEPTION, JSON_THROW expands to std::abort(), so Clang's
-Wunused-parameter breaks test-disabled_exceptions (since #5761).

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

* Skip the span_input_adapter sax_parse checks with deleted deprecated functions

The #5676 regression test (#5740) calls the deprecated
sax_parse(span_input_adapter&&, ...), which JSON_DELETE_DEPRECATED_FUNCTIONS
deletes, so ci_test_delete_deprecated_functions failed to build.

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

* Fall back to the first entry in test-diagnostics-optimized's to_json

clang-tidy (clang-analyzer-security.ArrayBound) flagged it->second for a
value not in the table. Use the same fallback as
NLOHMANN_JSON_SERIALIZE_ENUM; the test still fails with -Werror=array-bounds
on the headers from before #5585.

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

* Fix clang-tidy findings in tests from #5762 and #5774

- unit-regression2.cpp (#5762): const/auto for the destroy() test values;
  NOLINT the intended copy in check_destroy_edge_case().
- unit-serialization.cpp (#5774): build the expected strings with += instead
  of chained operator+ (performance-inefficient-string-concatenation).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-07 16:37:19 +02:00
Niels Lohmann e6f32bd28a Stricter fuzzer checks and boundary-value tests for buffers (#5774) 
* Check in the fuzzers that parsing without exceptions agrees

Each fuzzer driver now also parses its input with allow_exceptions =
false. That call must never throw a parse_error, must return a discarded
value where parsing with exceptions fails, and must return the same value
where it succeeds. Values are compared by their dump(), because NaN is
not equal to itself.

A plain !is_discarded() assertion, as suggested in #3642, would never
fail: the drivers parse with exceptions, so a result can never be
discarded.

tests/fuzzing.md describes the checks and notes that OSS-Fuzz and
CIFuzz already run LeakSanitizer, because their default address
sanitizer includes it.

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

* Use JSON_HAS_RANGE_VIEW_CONVERSION in the range view regression tests

#5728 combined the JSON_HAS_RANGES and MinGW conditions into
JSON_HAS_RANGE_VIEW_CONVERSION, but three test guards still spelled
them out.

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

* Test the serializer's buffers at their boundaries

The dump() indent overflow survived full line coverage because the tests
grew its buffer by only one step. This adds tests that land exactly on,
and one past, the limits of the other two serializer buffers:

- write_buffer (1024 bytes): strings of 1023, 1024 and 1025 bytes at the
  top level, and of 1022 and 1023 bytes inside an array, so that both
  guards in put_string() are hit at their boundary. Each is checked for
  dump() and for stream output.
- string_buffer (512 bytes, flushed when fewer than 13 bytes remain):
  runs of two-byte escapes, and a surrogate pair written with 14 bytes of
  room, right after a flush, and one escape later.
- The 8-byte bulk scan from the serializer side: 0 to 17 plain bytes
  followed by a quote, a control character, or a non-ASCII character.

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

* Test the chunked string and binary reads of all binary formats

The binary readers read strings and binary values in chunks of 4096
bytes. Only CBOR tested lengths around that size. MessagePack, UBJSON,
BJData and BSON now round-trip lengths 0, 1, 4095, 4096, 4097, 8192 and
100000 from vector and pointer input, and must report a truncated
payload as a parse error.

UBJSON reads binary values as arrays of numbers, so it is tested with
strings only. BJData binary values reach the chunked read only in
Draft 3. BON8 decodes strings byte by byte and does not use this path.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
 2026-10-07 08:50:12 +02:00