Commit Graph
1073 Commits
Author SHA1 Message Date
Niels Lohmann b15ec08275 Merge branch 'develop' into claude/const-json-pointer-assertion
Conflicts:
- docs/mkdocs/docs/api/basic_json/operator[].md: version history item 1 keeps develop's std::length_error fix note and appends the PR's runtime assertion note

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:42:02 +02:00
Niels Lohmann 6a073dbae4 Give operator>> a strong exception-safety guarantee (#5695)
operator>> parsed directly into its basic_json& target, so a parse
error left the target holding whatever was parsed before the error
instead of its previous value. With JSON_DIAGNOSTICS=1, that partial
value also violated the class invariant, because the parent pointers
of an array or object's elements are only set when the container is
closed, which a failed parse never reaches; copying such a value then
aborted in assert_invariant().

Fix it the way basic_json::parse() already handles this: parse into a
temporary and move it into the target only once parsing succeeds, so
the target is left unchanged if an exception is thrown.

Fixes #5652.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:13:34 +02:00
Niels Lohmann fdcc569eee Use only documented StringType members in json_pointer (#5692)
contains(const json_pointer&) and operator/=(std::size_t) (and hence
operator/(std::size_t)) used string_t operations that the StringType
template parameter documentation explicitly does not require:
comparing string_t with a const char* literal, c_str(), and
constructibility from std::string. This made both functions fail to
compile for a conforming custom StringType, even though the
documentation's own reference StringType satisfies the requirements.

Fix contains() to compare individual chars ('0'..'9') instead of
comparing string_t with const char* literals, and to call data()
(documented to be null-terminated) instead of c_str(). Fix
operator/=(std::size_t) to build the array-index token via the
existing detail::to_string<StringType> helper (ADL int_to_string() or
assignment from std::to_string()) instead of via std::to_string()
directly, matching how diff(), items(), and std::hash already convert
a std::size_t to a StringType.

Add regression tests to tests/src/unit-alt-string.cpp: contains() for
present/missing keys and indices, "-", a leading zero, and a
non-numeric token on an array, plus json_pointer::operator/(std::size_t).

Fixes #5666.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:13:31 +02:00
Niels Lohmann 6fc0d501f3 Move the user-defined string literals to <nlohmann/json_literals.hpp> and add JSON_NO_AUTOMATIC_UDLS (#5610)
* Add JSON_NO_UDLS to leave out the user-defined string literals

The bodies of operator""_json and operator""_json_pointer call the
parser, so every translation unit including the library instantiates it,
even if it never parses anything. Defining JSON_NO_UDLS leaves the
literals out entirely, which saves 15-35% compile time for such
translation units (#5294). Nothing changes if the macro is not defined.

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

* Mention JSON_NO_UDLS in the list of exported module symbols

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

* Move the user-defined string literals to <nlohmann/json_literals.hpp>

Following the review in #5294, the literals now live in their own header
instead of being removed entirely: <nlohmann/json.hpp> includes it at the
end unless JSON_NO_AUTOMATIC_UDLS (renamed from JSON_NO_UDLS) is defined,
so a project can opt out globally and include the header only where the
literals are used.

The header only uses public and standard macros, because the library's
internal macros are undefined at the end of json.hpp and the amalgamation
inlines macro_scope.hpp only once. For the same reason, the library no
longer defines and undefines JSON_USE_GLOBAL_UDLS, so a user's definition
is still visible to the header. The single-header copy is identical to
the multi-header one, as it only includes <nlohmann/json.hpp>. The module
always exports the literals.

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

* Fix CI: include cycle, GCC 4.8 literal operator spacing, and global UDLs off in the JSON_NO_AUTOMATIC_UDLS test

- Suppress clang-tidy misc-header-include-cycle on the intentional mutual
  include of json.hpp and json_literals.hpp.
- Use operator"" _json with a space for GCC 4.8 in the test's detection
  aliases, as the header does.
- Only test the global literal operators when JSON_USE_GLOBAL_UDLS is on.

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

* Declare the literal operators through a local macro

The GCC 4.8 spacing condition was repeated for both operator definitions
and the global using-declarations. NLOHMANN_JSON_LITERAL_OPERATOR(suffix)
now selects operator""##suffix or operator"" suffix in one place and is
undefined at the end of json_literals.hpp.

Suggested by gregmarr in review.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:08:17 +02:00
Niels Lohmann 67435c9c7e Give a deep copy its type only after its container exists (#5721)
When copying a value nested deeper than 128 levels, and an allocation
fails while an inner array or object is being copied, the partially
built copy ended up with an element typed array/object but holding a
null pointer. That element was already a fully constructed member of
its parent's container, so destroying the parent during stack
unwinding dereferenced the null pointer (release builds) or failed
assert_invariant() (debug builds), instead of letting std::bad_alloc
reach the caller.

copy_iteratively() set a pending worklist element's type right after
popping it, before the next loop iteration created its container in
copy_array_level()/copy_object_level(). Move that type assignment into
those two functions, right after the container is successfully
created, and drop the premature one in copy_iteratively(), so a
half-built element stays a null value - as copy_shallow()'s comment
already promised - until it can safely hold one.

Add a regression test to tests/src/unit-allocator.cpp that copies a
value nested 130 levels deep (both arrays and objects, with a
std::map- and an ordered_map-backed object_t) and fails every
allocation of the copy in turn: each attempt must throw std::bad_alloc
without crashing, and the source must stay unchanged.

Fixes #5640.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:08:00 +02:00
Niels Lohmann 2ea6d8c127 Require the found key to equal the looked-up key when comparing objects (#5720)
For an object type whose comparator treats unequal keys as equivalent
(for example a std::map with a case-insensitive comparator),
compare_iteratively() looked up a mismatched left key in the right
object with find(), which uses the object's own comparator, and
accepted whatever entry it found without checking that the keys are
actually equal. A case-insensitive comparator then found "KEY" for
"key", so two objects nested past the recursion bound (or at every
depth with JSON_NO_THREAD_LOCAL) could compare equal even though the
object type's own operator== - and basic_json itself, below the bound
- consider them different.

Accept the found entry only if its key equals (not just compares
equivalent to) the looked-up key.

Fixes #5655.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:56 +02:00
Niels Lohmann 66877675b1 Check the iterator range for binary values in basic_json(first, last) (#5719)
basic_json(first, last) treated value_t::binary like the structured
types (array, object) in the range check, so it always copied the
whole binary value regardless of the iterators, even for an empty
range such as (b.end(), b.end()). The other primitive types (number,
boolean, string) already reject such a range with
invalid_iterator.204, and erase(first, last) already does the same
for binary values, so this made the constructor inconsistent with
both. Move case value_t::binary into the group of checked primitive
types.

Also update the two matching passages in basic_json.md that describe
overload 7, and add a version-history note.

Fixes #5670.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:52 +02:00
Niels Lohmann 7fd6895788 Hide a discarded container's content from the parser callback (#5706)
When a parser callback rejects an object's or array's start event,
json_sax_dom_callback_parser kept calling it for everything inside
that container anyway: nested keys, values, and the start/end events
of containers below it. This contradicts parser_callback_t's own
documentation, which promises that discarding a container at its
start event also hides its content from the callback.

The same code path also kept a full copy of every key inside such a
discarded container in key_stack until the whole parse finished,
because the early return for values that are not stored skipped the
matching pop. Filtering out a large subtree is the main reason to use
a callback, so this made peak memory during the parse scale with the
size of the very subtree the callback was trying to skip.

Fix start_object(), start_array(), and key() so that a container
whose own start event was discarded, or that is nested inside one, is
never handed to the callback, and no longer pushes onto the key
stacks. A container whose start event was accepted but whose key was
rejected still gets its content reported, as documented ("the
callback is still called for the associated value, but its return
value has no further effect"); only its own bookkeeping is skipped
since it will not be stored.

Fixes #5643.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:48 +02:00
Niels Lohmann 6ae17630a4 Reject integral keys for contains(), find(), and count() at compile time (#5705)
j.contains(0), j.find(0), and j.count(0) used to compile: the literal 0 is
a null pointer constant, so it converts to a null const char*, and the
overloads taking const typename object_t::key_type& accepted it by
constructing a std::string from that null pointer, which is undefined
behavior (a crash with both libc++ and libstdc++). value(0, default_value)
had the same problem in C++11, where the object comparator is not
transparent.

Add deleted overloads for integral arguments to contains(), find()
(const and non-const), count(), and value() so that these calls are
compile errors in every supported language mode instead of crashing.
Calls with string, string_view, json_pointer, and size-typed element
access (at(), operator[](), erase()) are unaffected.

Fixes #5657.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:45 +02:00
Niels Lohmann 5bd766aa50 Move to_bson's binary subtype check into calc_bson_sizes (#5703)
to_bson() rejected a binary value's subtype above 255 (out_of_range.415)
in write_bson_binary(), which only has the binary_t, not the basic_json
value that holds it, so the exception was created with no JSON_DIAGNOSTICS
context even though the equivalent to_msgpack() check names the value's
path. The check also ran after the document size, all preceding elements,
and this element's header and length had already reached the output
adapter, so a caller-provided std::vector or std::string ended up holding
a truncated document.

calc_bson_sizes() already walks every value before anything is written,
to size embedded documents and arrays and to reject invalid keys
(out_of_range.409) up front. The subtype check now runs there instead,
in calc_bson_binary_size(), which is given the basic_json value so the
exception can use it as context. The now-redundant check in
write_bson_binary() is removed, since calc_bson_sizes() always throws
first if any binary value in the document has an oversized subtype.

Fixes #5675.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:41 +02:00
Niels Lohmann 4bb1b14b06 Trim the compiler-appended NUL from wide/UTF string literals too (#5702)
With JSON_STRICT_NUL_HANDLING defined to 1, parsing a wide, UTF-16,
UTF-32, or (C++20) UTF-8 string literal (e.g. json::parse(L"[1]"))
failed with parse_error.101 at the terminating NUL of the literal,
and accept() returned false. The array overload of input_adapter()
only dropped the compiler-added trailing '\0' for arrays of char,
so for wchar_t, char16_t, char32_t, and char8_t arrays that
terminator was passed to the parser as data, which the macro then
rejected.

Broaden the trimming to every character type that a string literal
can use (char, wchar_t, char16_t, char32_t, and, since C++20,
char8_t). Arrays of any other element type (unsigned char,
std::uint8_t, ...), as used for CBOR/MessagePack, are unaffected: a
trailing zero byte there is still read as genuine data.

Fixes #5658.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:37 +02:00
Niels LohmannandClaude Sonnet 5 bfe0f32d71 Fix std::terminate and null pointer access in input_stream_adapter (#5699)
Parsing from a std::istream crashed in two unusual but valid stream
states, both in input_stream_adapter:

- With eofbit in the stream's exceptions() mask, get_character() sets
  eofbit via is->clear(), which throws std::ios_base::failure. While
  that exception unwinds, ~input_stream_adapter() called clear() again
  to reset eofbit, which is still set and still in the exception mask,
  so it throws a second time out of the (implicitly noexcept)
  destructor and std::terminate() is called. The destructor now only
  calls clear() if a bit other than eofbit remains set, so the first
  exception can propagate normally.
- For an std::istream without a stream buffer (rdbuf() == nullptr,
  e.g. std::istream(nullptr)), the constructor stored the null
  pointer without checking it, and get_character() dereferenced it.
  input_adapter(std::istream&) now throws parse_error.101 for such a
  stream, the same as it already does for a null FILE* or char*.

Added regression tests to unit-deserialization.cpp and, for the
JSON_PRECISE_STREAM_POSITION variant of get_character(), to
unit-precise-stream-position.cpp; both crashed before this fix.
Documented the two exceptions in parse.md and operator_gtgt.md.

Fixes #5646.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
2026-09-30 20:07:33 +02:00
Niels Lohmann 44a88d85be Fix NLOHMANN_JSON_SERIALIZE_ENUM_STRICT's from_json message (#5698)
from_json built its out_of_range.410 message with "..." + j.dump(). If the
unmatched value is (or contains) a string with invalid UTF-8, that dump()
itself throws type_error.316, so the caller got type_error.316 instead of
the documented out_of_range.410; such strings can reach get<Enum>()
unvalidated, e.g. from from_cbor()/from_msgpack(). With a custom string_t,
j.dump() returns that type, and "const char*" + string_t does not compile
unless the type happens to provide operator+, so the macro failed to
compile for such types.

Build the message with detail::concat(), which appends any type exposing
data()/size() and always yields a std::string, and dump with
error_handler_t::replace so building the message itself cannot throw.

Added regression tests: an invalid-UTF-8 case in the existing strict-enum
test in unit-conversions.cpp, and a strict-enum use with alt_string (the
custom string_t from unit-alt-string.cpp) to cover the compile failure.

Fixes #5667.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:29 +02:00
Niels Lohmann 5b11a0282c Exchange the CustomBaseClass subobject in basic_json::swap() (#5697)
basic_json::swap() (and the friend swap() and the pre-C++20 std::swap
overload that forward to it) only exchanged m_data.m_type/m_data.m_value,
leaving each value's json_base_class_t subobject in place. This is
inconsistent with the copy and move constructors and copy assignment,
which all carry the base class along with the value, so after
a.swap(b) any metadata stored in a CustomBaseClass ended up attached to
the wrong value. Algorithms that mix swap() with moves, such as
std::sort, scrambled the metadata across the whole container.

Fix the member swap() to also exchange the json_base_class_t subobject
and extend the noexcept specifications of swap() and the friend swap()
accordingly.

Fixes #5653.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:24 +02:00
Niels Lohmann bfea6f36d3 Fix to_msgpack() reading the inactive number union member (#5694)
* Fix to_msgpack() reading the inactive number union member

basic_json stores number_integer and number_unsigned in a union, and
number_unsigned_t only has to be at least as wide as number_integer_t
(with the default types, both are 64-bit and have the same
representation). When number_integer_t is narrower, write_msgpack()
read the wrong union member in two places:

- The number_unsigned case wrote number_integer's bits instead of
  number_unsigned's, silently writing the wrong value whenever it
  did not fit in number_integer_t.
- The number_integer case (non-negative branch) picked the encoded
  width by comparing number_unsigned's bits, which is undefined
  behavior, though the value written was still number_integer's, so
  at worst a too-wide encoding was chosen.

Read the active member in both cases, like the other binary writers
(CBOR, UBJSON, BJData, BSON, BON8) already do.

Fixes #5644.

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

* Cast number_integer to number_unsigned_t only once in to_msgpack()

Addresses review comment by @gregmarr.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:19 +02:00
Niels Lohmann e444a66276 Copy values before inserting an initializer list into an array (#5693)
* Copy values before inserting an initializer list into an array

insert(pos, {...}) inserted wrong values when the initializer list
contained const references to elements of the array being inserted
into. json_ref stores only a pointer for a const lvalue, so the
initializer_list_t range passed straight to the array's range insert
aliased the array's own storage; std::vector::insert(pos, first, last)
may move or shift elements before copying from that range, so the
source elements were already stale by the time they were read
(different wrong results on libc++ and libstdc++).

Copy the referenced values into a temporary array_t first, then move
that temporary into place, so the source range never aliases the
array being modified.

Fixes #5656.

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

* Use the reserve_array helper in the initializer_list insert fix

The previous commit called array_t::reserve() directly on the
temporary buffer used to copy an ilist's values before inserting.
std::deque, a documented ArrayType (tests/src/unit-custom-array-type.cpp),
has no reserve(), so insert(pos, initializer_list) no longer compiled
for it. Use the existing detail::reserve_array() SFINAE helper (already
used by the SAX DOM parser) instead, which leaves array types without
reserve() untouched.

Added a regression check that deque_json::insert(pos, {...}) compiles
and handles the aliasing case from #5656.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:16 +02:00
Niels Lohmann 1151826508 Take diff()'s fast path unless the object type reorders members (#5691)
* Take diff()'s fast path unless the object type reorders members

For every object type except an insertion-ordered one like ordered_map,
diff() no longer produced a member-by-member patch when target had a key
that sorts before a key the two objects share: it fell through to the
slow path, which removes every member of source and re-adds every member
of target, instead of just adding the new key.

#5465 added an order check to require the fast path to also reproduce
target's member order, needed because ordered_map's patch()-driven "add"
appends a new member at the end. The check compared the common keys'
order between source and target and also required that every added key
come after every common key in target's order ("new_keys_form_suffix").
The comment above it argued this check is always true for std::map, and
that reasoning is correct for the order of the common keys themselves,
but not for new_keys_form_suffix: a std::map iterates in sorted key
order, so a new key that sorts before an existing common key is
enumerated between common keys, making new_keys_form_suffix false even
though std::map's own key order does not need reordering at all - it
places every member itself, regardless of insertion history, so a
member-by-member diff already reproduces target's iteration order.

Only require the order check for an object type that keeps insertion
order, using the same detail::is_ordered_map trait the library already
uses to recognize such an object type in set_parent(). Every other
object type - std::map in key order, a hash map in an order its
operator== ignores - always takes the fast path.

Added a regression test to unit-json_patch.cpp: the issue's example now
yields a single "add" op for json, while ordered_json still takes the
slow path to reproduce target's member order.

Fixes #5639.

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

* Only track the target key order in diff() for insertion-ordered objects

common_keys_target_order and new_keys_form_suffix are only read when object_t keeps its members in insertion order; skip building them otherwise. Addresses review comment by @gregmarr.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:10 +02:00
Niels Lohmann 6218aa212b Throw std::length_error for operator[](SIZE_MAX) instead of corrupting the array (#5687)
For idx == SIZE_MAX, the non-const array operator[] computed the new size as
idx + 1, which wraps to 0. resize(0) then emptied the array, and the
subsequent operator[](idx) on the now-empty vector wrote one element before
its buffer. Every other too-large index (e.g. SIZE_MAX - 1) already went
through resize(), which throws std::length_error and leaves the array
unchanged; SIZE_MAX was the one value for which the overflow bypassed that
safety net.

Add a guard that throws std::length_error before computing idx + 1 when idx
is the largest representable size_type value, so the array is left
unchanged, matching the exception vector::resize() already throws for
smaller (but still too large) indices.

Fixes #5647.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:06 +02:00
Niels Lohmann 42f89e3130 Let to_json(std::optional<T>) propagate exceptions from T's to_json (#5684)
* Let to_json(std::optional<T>) propagate exceptions from T's to_json

The overload was marked noexcept even though its body assigns *opt to
the JSON value, which calls T's to_json (or allocates for std::string,
std::vector, or json). Any exception from there -- a user-defined
to_json reporting an error, or std::bad_alloc -- called std::terminate()
instead of propagating. The noexcept also made basic_json's converting
constructor noexcept(true) for std::optional<T>, so json j = opt; could
not report the error either.

Fixes #5642.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix CI: make to_json(std::optional<T>) conditionally noexcept

GCC's -Wnoexcept (an error in ci_test_gcc) fired at to_json_fn's
noexcept(noexcept(to_json(j, val))): after dropping the unconditional
noexcept, to_json(std::optional<int>) had no exception specification
although GCC could prove its body cannot throw. It also made
json(std::optional<int>) lose its noexcept.

Declare the overload noexcept exactly when assigning the contained
value to the JSON value is (std::is_nothrow_assignable<BasicJsonType&,
const T&>), which is what the body does. std::optional<int> is noexcept
again; a T whose to_json may throw still propagates the exception.
Static assertions in the test check both cases.

The test's throwing to_json triggered -Wmissing-prototypes and
-Wmissing-noreturn (clang) and -Wmissing-declarations and
-Wsuggest-attribute=noreturn (GCC). Move the type and its to_json into
an anonymous namespace, mark the function [[noreturn]], and compile
them only without JSON_NOEXCEPTION, like the test that uses them.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:07:02 +02:00
Niels Lohmann 6d7845d207 Fix deprecated json_pointer/string operator== warning in value() (#5683)
value(KeyType&&, default) is constrained on is_comparable_with_object_key,
which passes KeyType as a reference. is_comparable's dispatch on
is_json_pointer_of<A, B> only matches a json_pointer as a plain type or a
plain reference, so a const-qualified reference (as produced when KeyType
is deduced from a json_pointer argument) fell through to
is_comparable_no_json_pointer, which instantiates the deprecated
json_pointer/string comparison operators. This made ordered_json's
transparent comparator (and any transparent comparator on a custom string
type) warn under -Wdeprecated-declarations when calling
value(json_pointer, default), even though no such comparison is ever
performed. at() was already fixed for this in #5289, which does not use
is_comparable_with_object_key.

Strip references and cv-qualifiers with uncvref_t before the
is_json_pointer_of dispatch, so any reference-to-json_pointer is
recognized regardless of qualifiers.

Fixes #5664.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:59 +02:00
Niels Lohmann 678fd3017b Fix element path for map/unordered_map JSON_DIAGNOSTICS errors (#5681)
When converting a JSON array to std::map or std::unordered_map with a
non-string key, each element must itself be a [key, value] array. If an
element is not an array, from_json() threw type_error 302 with the outer
array's value (&j) as the exception context, so with JSON_DIAGNOSTICS
enabled the message pointed at the whole array instead of the offending
element (e.g. "(/outer/m)" instead of "(/outer/m/2)"), even though the
message text already described the element's type.

Both from_json() overloads now pass the element (&p) as the context, so
the reported JSON Pointer matches the type named in the message, the
same way std::vector<std::vector<T>> and similar conversions already do.

Fixes #5668.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:55 +02:00
Niels Lohmann fc4c9c3446 Fix clear() to also reset the subtype of a binary value (#5680)
* Fix clear() to also reset the subtype of a binary value

clear() on a binary value cleared the bytes but left the subtype
untouched, so the result was not equal to a default-constructed
binary value even though the documentation says clear() has the same
effect as *this = basic_json(type()). The fix calls
byte_container_with_subtype::clear_subtype() alongside the existing
clear() call.

Extended the "filled binary" clear() test in unit-modifiers.cpp with
a case that uses a subtype, since the existing cases only covered
binary values without one.

Fixes #5669.

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

* Fix the table alignment in clear.md

Addresses review comment by @gregmarr.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:51 +02:00
Niels Lohmann 68beba727c Fix from_json() for enums with underlying type bool (#5679)
get_arithmetic_value() rejects boolean_t, so the default from_json()
for enums failed to compile for an enum whose underlying type is
bool (e.g. enum class Flag : bool { off, on }), even though the
matching to_json() serializes such enums as an unsigned number.

Read the underlying value through number_unsigned_t in that case,
matching what to_json() writes, then cast back to the underlying
type before constructing the enum.

Fixes #5671.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:46 +02:00
Niels Lohmann 0050d0f7a4 Share one nesting depth limit between all bounded descents (#5637)
Copying and comparing stopped their descent at
basic_json::nesting_depth_limit(), while serializing, hashing and
merging used detail::recursion_depth_limit(). Both were 128, but
nothing kept them equal. The thread-local count now tests against
detail::recursion_depth_limit() as well, and a static_assert keeps
the limit small enough for the byte that holds the count.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:43 +02:00
Niels Lohmann 6a8a7735ed Do not throw in contains() for an empty array reference token (#5614)
* Do not throw in contains() for an empty array reference token

json_pointer::contains() rejected malformed array indices, but an empty
reference token (e.g. "/a/" where "a" is an array, or "/" on an array)
passed every check and reached array_index(), which throws
out_of_range.404. contains() must not throw (cf. #5395), so it now
returns false for an empty token. at() still throws out_of_range.404.

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

* Fix CI: bind j_nested_const by reference in the json_pointer test

clang-tidy (ci_clang_tidy) flagged the new test with
performance-unnecessary-copy-initialization: the local copy
j_nested_const of j_nested is never modified. Bind it as a const
reference instead; it still exercises the const overloads of at() and
contains().

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:39 +02:00
Niels Lohmann 65af260117 Move instead of deep-copy ordered_json values when an object grows (#5609)
* Move instead of deep-copy ordered_json values when an object grows

ordered_map keeps its elements in a std::vector<std::pair<const Key, T>>.
With a std::string key, that pair is not nothrow move constructible (the
const key has to be copied), so std::vector copies every element when it
reallocates. For ordered_json, this deep-copies every member value an
object already holds, including whole nested subtrees, on each growth
step.

Grow the storage in ordered_map instead, copying the keys and moving the
values. This happens in two phases, so the strong exception guarantee is
kept without try/catch. The first phase may throw, but only touches a
temporary buffer: it copies the keys, value-initializes the values, and
constructs the new element. The second phase moves the values (noexcept)
and swaps the buffers. Because the new element is constructed before any
value is moved, arguments that refer to elements of the container stay
valid, as with std::vector. Types that cannot take this path keep the
std::vector behavior.

Parsing into ordered_json (ParseStringOrdered, Apple M1 Max, clang -O3):
twitter 3.20 -> 1.70 ms, citm_catalog 7.73 -> 3.67 ms, jeopardy 219 ->
177 ms, canada unchanged. The number of allocations for twitter and
citm_catalog drops by two thirds.

Also add ParseStringOrdered rows to the benchmarks, and document the
growth behavior and the exception safety of ordered_map.

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

* Fix CI: skip std::pair noexcept assumptions on EDG-based compilers

ci_icpc and ci_nvhpc failed to compile unit-ordered_map.cpp: the static
assertion that std::pair<const std::string, ordered_json> is not nothrow
move-constructible fails there. The EDG front end (Intel icpc 2021.10,
NVIDIA nvc++ 25.5) considers the defaulted move constructor of
std::pair<const Key, T> noexcept even if copying Key can throw. With these
compilers, std::vector already moves such elements itself when it grows,
and ordered_map correctly leaves growing to it.

The same misjudgement makes std::vector call std::terminate when a key copy
throws during growth, so the exception-safety test with throwing_key would
abort on these compilers as well.

Skip the static assertion and the exception-safety section when __EDG__ is
defined. Verified with icpc 2021.10 (-std=gnu++11) and nvc++ 25.5 (C++11 and
C++17) on Compiler Explorer: unit-ordered_map and unit-disabled_exceptions
build and pass.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:34 +02:00
Niels Lohmann d268eaa693 Convert floats with Eisel-Lemire when std::from_chars is unavailable (#5617)
* Convert floats with Eisel-Lemire when std::from_chars is unavailable

Float tokens that Clinger's fast path cannot convert (e.g. the 17-digit
coordinates of canada.json) went to strtod unless std::from_chars was
available. It is not used in C++11/14, and not with libc++, which does not
define __cpp_lib_to_chars. The Eisel-Lemire algorithm (after fast_float's
compute_float) now converts them with integer arithmetic, correctly rounded
for any token with at most 19 significant digits. Longer tokens are
truncated; the result is used if w and w + 1 round alike, else strtod
decides as before. Overflow still yields infinity (out_of_range.406).

The table of powers of five (fast_float's) lives in pow5_table.hpp; a unit
test recomputes every entry with big-integer arithmetic. Further tests:
known values generated with Python (whose float() is correctly rounded),
200,000 round trips through to_chars, and the 128-bit multiplication and
leading-zero count against big-integer references (both with and without a
128-bit type). Checked against strtod on 6.5 million tokens, among them
60,000 exact halfway cases: no difference.

json::parse on canada.json: -8.6% (C++11), -7.6% (C++17, Apple clang);
other files unchanged. Compile time of a TU including json.hpp: +0.7%.

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

* Fix CI: unused parse result and find() == npos in the Eisel-Lemire tests

GCC (-Werror=unused-result) rejected CHECK_THROWS_WITH_AS(json::parse(...))
because parse() is [[nodiscard]]; assign the result to a dummy json as the
other tests do. clang-tidy flagged longer.find('.') == npos with
abseil-string-find-str-contains; store the position in a variable first.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:26 +02:00
Niels Lohmann 5b9ffae8bb Move the float conversion chain out of the lexer (#5616)
lexer::convert_number() converted float tokens with std::from_chars (when
available), Clinger's fast path, and the locale-aware strtod fallback, all
as lexer members. They are now free functions in number_parse.hpp:

- convert_float_fast(): std::from_chars, then Clinger's fast path, skipped
  when the mantissa has too many significant digits
- convert_float_locale_aware(): strtof/strtod/strtold with the decimal point
  of the current locale, retried when the locale changed (#5198)

so that other code converting JSON number tokens gets the same values. No
change in behavior; the lexer no longer includes <clocale> and <cstdlib>.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:06:25 +02:00
Niels Lohmann fc03b9912e Look up the locale decimal point at conversion time, not lexer construction (#5597)
* Look up the locale decimal point at conversion time, not lexer construction

The lexer read localeconv()->decimal_point once in its constructor and wrote
that character into token_buffer in place of '.'. The strtod fallback then
used the locale current at conversion time, so an LC_NUMERIC change in
between (parser callback, SAX handler, another thread) truncated the value
in release builds and fired the endptr assertion in debug builds.

token_buffer now always holds '.'. Only the strtof/strtod/strtold fallback
depends on the locale: it looks up the decimal point right before the call,
restores '.' afterwards, and repeats the conversion if the locale changed in
between. As a side effect, std::from_chars and Clinger's fast path now also
apply under locales whose decimal point is not '.'.

Fixes #5198

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

* Stop the strtod retry loop when the decimal point is unchanged

convert_float_locale_aware() repeated the conversion until strtod
consumed the whole token, assuming an early stop can only mean a locale
change. Under a locale whose decimal point is not a single character
(e.g. the two-byte U+066B of ar_EG.UTF-8, ar_SA.UTF-8, or fa_IR.UTF-8,
all available on macOS), the in-place substitution can never succeed,
so parsing any float that reaches the strtod fallback (for example
3.14159265358979323846 at C++11) hung forever. Before this branch, the
same input was truncated.

Retry only if the decimal point changed since the previous attempt;
otherwise keep the value strtod parsed so far, as before. Add a test
that parses such numbers under a multi-byte decimal point locale; it
hangs without this change.

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

* Fix -Weffc++ errors in the #5198 locale test

GCC's -Weffc++ (an error in ci_test_gcc and ci_test_standards_gcc)
rejected LocaleSwitchingSax: it has a pointer data member but does not
declare its copy operations, and its vectors are not initialized in the
member initializer list. Store the locale name as a std::string and give
the vectors brace initializers, like SaxEventLogger in
unit-deserialization.cpp.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-28 17:56:11 +02:00
Niels Lohmann 9e1a09eec0 Name the key type when rejecting non-string CBOR/MessagePack map keys (#5594)
* Name the key type when rejecting non-string CBOR/MessagePack map keys

CBOR and MessagePack allow map keys of any type, but JSON object keys
are always strings, so such maps are rejected. The error so far was the
one for a malformed string (e.g. "expected length specification
(0xA0-0xBF, 0xD9-0xDB); last byte: 0xC0" for a nil key), which does not
tell the user what went wrong. Report the type of the key instead:

  syntax error while parsing MessagePack object key: only string keys
  are supported, but found nil; last byte: 0xC0

The exception id (parse_error.113) and type are unchanged. Malformed
string keys and a missing key keep their previous messages. Document
the restriction on the CBOR and MessagePack pages.

Refs #2766, #3381

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

* Point the MessagePack key note to the spec's profile section

The note linked to "Serialization: type to format conversion", which says nothing about key types. Restricting map keys to strings is only mentioned in the "Profile" section (under "Future discussion") as an example of a JSON-compatible profile, so link there and describe it as such instead of as a permission.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-28 17:51:07 +02:00
Niels Lohmann 93fe62fc0b Assert on missing array indices in const operator[] and document the JSON pointer case
The const operator[] overloads are unchecked by design, and a missing key
or index is undefined behavior. The key overload guards this with a
runtime assertion, but the index overload did not, although the element
access documentation says an assertion fires in both cases. The const
JSON pointer overload inherits both through json_pointer::get_unchecked(),
so a pointer to a missing array index read out of bounds even in debug
builds, and its documentation promised out_of_range.404 for any pointer
that cannot be resolved.

Add JSON_ASSERT(idx < size()) to const operator[](size_type), which also
covers the index leg of the const JSON pointer overload. Document the
undefined behavior for the const JSON pointer overload in operator[].md
and in the runtime assertions page. Release builds are unchanged.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 23:17:42 +02:00
Niels Lohmann 1e101ecac1 Add BON8 support (#2998)
* Add BON8 support

Add to_bon8/from_bon8 and input_format_t::bon8 for BON8, a binary format
that uses the byte values that cannot begin a UTF-8 character as type
markers, so strings need no length prefix. It is the most compact of the
supported binary formats on the benchmark files.

The reader is non-recursive like the other binary readers. A string ends
at the first byte that cannot continue it, so the reader hands the one or
two bytes it reads past a string back to the value that follows. The
writer produces the canonical representation of the specification, except
for NFC normalization; its output is identical to that of the reference
implementation (HikoGUI) on all files of the test data.

The round-trip tests need the .bon8 files of json_test_data 3.2.0.

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

* Address review comments

- Reuse detail::validate_one_utf8 to check strings in to_bon8; the error
  now names the first byte of the invalid sequence.
- Document that to_bon8 leaves bytes in the output adapter on an
  exception, and that string_open is only an output of write_bon8_marker.
- Explain why the pushback buffer of the BON8 reader cannot overflow.

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

* Select the BON8 float prefix by type

get_bon8_float_prefix only depends on the type of its argument, so make
the type a template parameter instead of passing an unused value.

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

* Rename a test variable that Flawfinder mistakes for read()

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

* Fix the BON8 CI failures

- compare the float in write_bon8_float with number_float_t constants,
  so GCC does not warn about a float-to-double conversion
- mark check_bon8_utf8's context as used when exceptions are disabled
- choose the compact float prefix in a helper rather than with nested
  conditional operators (clang-tidy)
- use auto for the cast in the BON8 integer reader (clang-tidy)
- write the int32 minimum test values as long long literals (MSVC C4146)

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

* Amalgamate

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

* Read BON8 strings in bulk from contiguous input

- copy the valid UTF-8 of a string in one step when the input is
  contiguous (twitter.json is read in 1.68 instead of 2.52 ms,
  jeopardy.json in 196 instead of 297 ms, close to CBOR and MessagePack)
- share the new valid_utf8_prefix() with the writer's UTF-8 check, which
  now skips ASCII 8 bytes at a time
- let the fuzzer check that contiguous and stream input give the same
  value or error, and test both paths in the unit tests
- clarify that a second 0xFF after a string is an empty string

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

* Link the BON8 functions from the other binary format pages

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

* Name the bulk scan flag after the input, not BON8

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

* Read BSON keys in bulk from contiguous input

BSON keys (and array indices) are C-style strings, which were read byte
by byte. For contiguous input they are now read up to their \x00-byte in
one step, using the same bulk_scan flag as BON8 strings: twitter.json is
read in 1.46 instead of 2.01 ms, citm_catalog.json in 2.93 instead of
3.33 ms, jeopardy.json in 182 instead of 207 ms. canada.json, whose keys
are almost all one-digit array indices, takes 2 % longer.

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

* Fix the BON8 CI failures of the bulk-read tests

- skip the contiguous-versus-stream tests of BON8 strings and BSON keys
  when exceptions are disabled: they catch the parse errors of invalid
  input, and without exceptions the library aborts instead
- use static_cast for the int64 test value (google-readability-casting)

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

* Move the explicit basic_json instantiation into its own test file

Linking test-regression3_cpp20 with clang and MinGW failed with
"relocation truncated to fit: IMAGE_REL_AMD64_REL32 against `.rdata'",
as test-regression2 did before #5511. The explicit instantiation of
basic_json<> for #4825 compiles every member function, including the
BON8 reader and writer, into that object, and it was already close to
the limit (2,226,104 bytes on develop, 2,234,960 with BON8; clang -O1,
C++20).

Give the instantiation a file of its own: unit-regression3 is now
1,594,736 bytes and unit-explicit_instantiation 1,095,064. The new file
mentions JSON_HAS_CPP_17 and JSON_HAS_CPP_20 so it keeps being built
for the C++17 standard the regression was about.

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

* Convert the bytes of the BON8 test strings explicitly

The str() helper constructed a std::string from a byte range, which
converts each unsigned char implicitly; -fsanitize=integer reports that
for bytes of 0x80 and above (ci_test_clang_sanitizer).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 16:56:21 +02:00
Kartikey Negi 6bd106893a Fix CBOR tag handling in cbor_tag_handler_t::store for non-binary items (#5559)
When using cbor_tag_handler_t::store, tags 0xD8-0xDB previously assumed
that the tagged item was a byte string, unconditionally attempting to
parse binary data and failing on valid CBOR documents containing tags
applied to integers, strings, arrays, or objects (such as self-describe
tag 55799).

Check whether the tagged data item is a byte string (0x40-0x5B or 0x5F).
If it is a byte string, store the subtype on the binary value as before.
Otherwise, iteratively process the tagged value in the driver loop using
item_read so that chained tags do not consume native stack space.

Part of #5316.

Signed-off-by: ReturnKartikey <kartikeynegi2000.work@gmail.com>
2026-09-27 14:28:55 +02:00
Niels Lohmann f7972970a4 Throw instead of writing MessagePack lengths beyond UINT32_MAX (#5584)
* Throw instead of writing MessagePack lengths beyond UINT32_MAX

MessagePack stores the length of a string, binary value, array, or
object in at most 32 bits. For a larger value, to_msgpack wrote no length
at all, so the output could not be read back. It now throws
out_of_range.412, which BSON already uses for its 32-bit length fields.

The check lives in one function, so each length is written by an
if/else chain that ends in a plain else, without a condition that can
never be false. It is tested with string and binary types that report a
size beyond UINT32_MAX without allocating it, like the BSON tests do.

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

* Fix the CI failures of the MessagePack length check

- mark to_msgpack_length's value as used when exceptions are disabled
  (-Wunused-parameter, misc-unused-parameters)
- put "Exception safety" before "Exceptions" in to_msgpack.md, as the
  documentation style check requires
- create the test's string value from its type: constructing it from a
  beyond_uint32_string_t considers the std::filesystem::path conversion,
  which libstdc++ 10 reports as ambiguous for a class derived from
  std::string (clang 13)

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

* Skip the MessagePack string length test for clang with libstdc++ 10

C++17 builds consider the std::filesystem::path conversion for the
string type, and with clang and libstdc++ 10 that conversion is
ambiguous for a class derived from std::string. Creating the value from
its type did not avoid it, since any basic_json with that string type
instantiates the check. The binary and ext cases are still tested there.

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

* Keep the MessagePack string test type and its alias in one block

astyle indented the alias oddly when it had an #ifdef of its own after
the binary alias; declare it right after the string type, in the same
block.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 14:28:16 +02:00
Niels Lohmann 6178982b8d Compare unordered objects by key below the nesting bound (#5582)
* Compare unordered objects by key below the nesting bound

Values nested deeper than the nesting bound are compared without the
call stack, walking both objects entry by entry. Two equal objects of a
type that enumerates its entries in no fixed order - std::unordered_map,
say - can be walked in different orders, so they compared unequal, and
a deep copy compared unequal to its original. std::unordered_map's own
operator== does not depend on the order, which is what applies above the
bound.

Where the keys differ, equality now finds the entry by its key instead.
An ordering, and ordered_map, whose operator== compares its entries in
sequence, still decide by the key.

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

* Test unordered object equality without std::unordered_map

basic_json<std::unordered_map> instantiates std::pair<const string,
basic_json> while basic_json is still incomplete. The standard does not
require std::unordered_map to support that, and libstdc++ 6 to 9 as well
as the EDG front ends of icpc and nvc++ reject it, which broke the build
of unit-comparison on those CI jobs.

The test now uses an object type derived from std::map (which, as the
default object type, works everywhere) whose comparator orders keys
ascending or descending as chosen at construction, and whose operator==
does not depend on the order of the entries - the property of
std::unordered_map the test is about.

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

* Compare the test object type's entries with std::all_of

clang-tidy (readability-use-anyofallof) asked for std::all_of instead of
the loop in unordered_object_t's operator==. The entry type is spelled
out, as C++11 needs typename for base_type::value_type and C++20
reports it as redundant.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 14:21:58 +02:00
Niels Lohmann 4fa95d9810 Remove unreachable branches from the binary writer (#5583)
Coverage reported conditions in the binary writer that can never be
false, and marked the code behind them with LCOV_EXCL. Remove them
instead of excluding them:

- CBOR writes the length of a string, binary value, array, or object
  exactly like an unsigned integer, only with another major type. One
  function, write_cbor_head(), now writes both, so the integer tests
  cover every width and the four excluded 64-bit length branches are
  gone.
- A last `else if` whose condition holds for every remaining value
  (an unsigned value at most UINT64_MAX, a signed one in the range of
  int64_t) is now a plain `else`.
- Whether a signed integer fits into an int64 for UBJSON and BJData is
  decided by its type at compile time. Only an integer type wider than
  64 bits gets a range check and the high-precision fallback.
- The private get_impl(boolean_t*) was never called.

The UBJSON type prefix 'H' of an optimized container of unsigned
integers beyond the range of int64 was reachable although excluded; it
is tested now.

The output is unchanged.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-27 14:18:46 +02:00
Dadi Reddy Sai Praneeth Reddy fe4a544c7e handled when size exceed uint32 (#5515)
* handled when size exceed uint32

Signed-off-by: dsp0redy <saipraneethreddy.dadireddy@gmail.com>

* addressed review comments

Signed-off-by: dsp0redy <saipraneethreddy.dadireddy@gmail.com>

* updated unit test

Signed-off-by: dsp0redy <saipraneethreddy.dadireddy@gmail.com>

* added amalgamation patch

Signed-off-by: dsp0redy <saipraneethreddy.dadireddy@gmail.com>

---------

Signed-off-by: dsp0redy <saipraneethreddy.dadireddy@gmail.com>
2026-09-27 14:17:32 +02:00
Niels Lohmann 95e9a5931c Write BSON in linear time, without recursing per nesting level (#5553)
* Write BSON in linear time, without recursing per nesting level

to_bson() had two problems with nested values:

- It recursed once per nesting level, so a value nested deeply enough -
  100,000 levels on an 8 MiB stack - exhausted the call stack and
  terminated the process, although parse() accepts such values without
  complaint.
- BSON prefixes every document and array with its length. The writer
  computed that length by walking the entire value below it, again for
  every nested document it wrote, which made serializing O(size x depth).
  A 200-level document took 30 ms instead of 1.

Both passes are now iterative, and each length is computed exactly once:

- calc_bson_sizes() computes the length of every document and array in
  one pass, each from the lengths of its entries, into a table ordered
  the way they are written.
- write_bson_document() then writes the document, taking each length from
  the table.

Everything observable is unchanged, as a differential test against
develop confirms byte for byte:

- The same bytes are written.
- A key containing U+0000 still throws out_of_range.409 for the same
  first key, with the same diagnostics path, before anything is written.
- A document too large for BSON still throws out_of_range.412 before
  anything is written.
- A binary subtype above 255 still throws out_of_range.415 after the
  same partial output.

Only the enclosing objects and arrays are kept on a stack, so a flat
document allocates nothing for it. Measured against develop (clang -O3,
median of 201 runs): flat objects unchanged, flat arrays 37% faster (the
array length was computed twice), a nested 3,000-object document 2x
faster, a 200-level document 33x faster.

to_bson.md documented the quadratic complexity since #5334; it is linear
again.

Fixes #5392 for BSON, and #5308.

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

* Do not require a default-constructible string_t in the BSON writer

GCC 4.9 and MSVC rejected the test's huge_string_t, which has no default
constructor; develop never default-constructed string_t here either.

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

* Let the BSON index-name helper only fill its output parameter

It returned a reference to the string it filled, so callers held a second
name for index_name. Addresses review feedback.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 21:56:39 +02:00
Niels Lohmann 1e44262091 Make JSON_STRICT_NUL_HANDLING part of the ABI tag (#5560)
* Make JSON_STRICT_NUL_HANDLING part of the ABI tag

JSON_STRICT_NUL_HANDLING (#5534) changes the bodies of inline functions:
the lexer's handling of '\0' and input_adapter() for char arrays. So
translation units compiled with and without it define the same functions
differently, an ODR violation - the case the ABI tag exists for, as with
JSON_BRACE_INIT_COPY_SEMANTICS (_bics). It now appends _snul to the inline
namespace. The macro is new in 3.13.0, so no existing namespace changes.

Its default moves to abi_macros.hpp, and it is only #undef'd without
JSON_TEST_KEEP_MACROS, as for the other ABI macros. The ABI config tests,
the namespace docs, the macro's docs and the Natvis file cover the new tag.

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

* Amalgamate

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 21:54:11 +02:00
Niels Lohmann c60a0bc336 Allocate the deep copy's key scratch space with the provided allocator (#5573)
* Allocate the deep copy's key scratch space with the provided allocator

The iterative deep copy builds each object's keys in a temporary vector of
key/value pairs before handing them to the object's range constructor. That
vector holds basic_json values, so like the values themselves it now uses
AllocatorType instead of std::allocator.

Also document that AllocatorType covers the JSON values, while most
temporary storage still uses std::allocator.

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

* Count allocate_at_least in the scratch-counting test allocator

From C++23 on, libc++'s containers allocate through allocate_at_least when
the allocator has one. The test allocator inherited it from std::allocator,
so the scratch allocations were not counted and the test failed on Xcode.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 21:53:49 +02:00
Niels LohmannandClaude Sonnet 5 d19f7f5dce Fix BSON conformance issue (#5185)
* 🐛 fix BSON conformance issue

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

* 🐛 fix BSON conformance issue

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

* 🐛 reject ill-formed UTF-8 in CBOR/MessagePack/BSON text strings at decode time (#5531)

from_cbor()/from_msgpack()/from_bson() copied the raw bytes of a decoded
text string into the resulting json value without any UTF-8 validation,
even though RFC 8949 §3.1 (CBOR) and the MessagePack/BSON specifications
all require text strings to be valid UTF-8. Malformed input only failed
later, if the value was dump()'d, with a type_error.316 - so the
allow_exceptions=false pattern used specifically to get a discarded
sentinel instead of an exception did not discard this category of
malformed input, unlike every other kind of malformed binary input this
library rejects at decode time (see #5529).

Fix this at the single choke point shared by BSON/CBOR/MessagePack/UBJSON
string reads, binary_reader::get_string(): validate the bytes with the
UTF-8 DFA right after they are read, and report failures the same way as
every other binary_reader error (parse_error.113), so allow_exceptions
and strict discarding behave consistently. get_binary()/binary blob reads
are untouched and still accept arbitrary bytes, since only text strings
are required to be UTF-8.

There were two independent implementations of a UTF-8 validator: the
lexer's streaming scanner, and the serializer's Hoehrmann DFA used by
dump_escaped_impl(). Rather than write a third, the serializer's decode()
function, its utf8d table and the UTF8_ACCEPT/UTF8_REJECT constants are
extracted into detail/string_utils.hpp (a low-level header already
included before both detail/input/ and detail/output/), alongside a new
is_valid_utf8() helper built on the same decode() step. serializer.hpp's
dump_escaped_impl() now calls the shared decode(), so there is exactly
one UTF-8 validator in the codebase; dump()'s exact type_error.316
messages and byte-index reporting are unchanged (see the added
regression-guard test in unit-serialization.cpp).

Claude-Session: https://claude.ai/code/session_01N4RQ1Ahan5YAGbnAQGjZTY

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

* ⚡ validate only newly read bytes of binary-format strings

get_string() validated the whole result after each call, but get_bytes()
appends to it and CBOR indefinite-length strings collect all chunks in
the same result, so every chunk re-validated everything read before it.
An input of many small chunks took quadratic time (80000 one-byte chunks,
160 KB of input, took about 7 seconds). Only the newly read bytes are
validated now, which also matches RFC 8949's requirement that every
chunk is valid UTF-8 on its own.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
2026-09-25 20:45:28 +02:00
Niels Lohmann 632a5812a8 Support zero-member types in NLOHMANN_DEFINE_TYPE_* macros (#4041) (#5272)
* Support zero-member types in NLOHMANN_DEFINE_TYPE_* macros (#4041)

NLOHMANN_DEFINE_TYPE_INTRUSIVE(Type) and its 11 sibling macros produced
broken code for types with no members to serialize. Invoking a variadic
macro so __VA_ARGS__ is empty is only standard-conforming since C++20,
so a plain __VA_OPT__ fix (as tried in #5142) breaks every pre-C++20
build under -pedantic. Instead, make all 12 macros purely variadic and
dispatch on argument count using a sentinel-padded extension of the
existing NLOHMANN_JSON_GET_MACRO idiom, giving full C++11-C++26 support
with no feature-test gate.

Verified against real GCC 16 and Clang at -std=c++11/14/17/20 with
-pedantic -Werror -Wvariadic-macros: zero regressions in the existing
unit-udt_macro.cpp suite plus 12 new zero-member test cases.

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

* Fix CI failures in zero-member NLOHMANN_DEFINE_TYPE_* macros

Three issues surfaced on PR #5272's real CI that weren't caught by
local testing against a narrower flag set:

- GCC -Werror=noexcept: the four truly-empty from_json bodies (plain
  INTRUSIVE/NON_INTRUSIVE, with and without _WITH_DEFAULT) provably
  never throw but weren't declared noexcept; mark them noexcept
  explicitly. to_json and the derived-type from_json overloads are
  left alone since they genuinely can throw (object assignment /
  delegating to the base class's from_json).
- clang-tidy bugprone-macro-parentheses: false positive on the same
  8 zero-member bodies (Type/BaseType used purely as declarator
  types); suppressed with NOLINTNEXTLINE comments in the same style
  already used elsewhere in this file (see NLOHMANN_JSON_SERIALIZE_ENUM).
- MSVC's traditional preprocessor doesn't fully expand
  NLOHMANN_JSON_CAT(prefix, NLOHMANN_JSON_TYPE_TAG(...))(...) in one
  pass, which broke a pre-existing one-member usage in
  unit-regression2.cpp with syntax errors. Wrap all 12 public
  dispatcher macros in an extra outer NLOHMANN_JSON_EXPAND(...),
  matching the pattern NLOHMANN_JSON_PASTE already uses for the same
  MSVC quirk.

Re-verified against real GCC 16 and Clang at -std=c++11/14/17/20 with
-pedantic -Werror -Wvariadic-macros -Wnoexcept, including the exact
files that failed in CI (unit-udt_macro.cpp, unit-regression2.cpp),
against both the modular headers and the re-amalgamated single header.

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

* Fix clang-tidy misc-const-correctness in unit-udt_macro.cpp

The four zero-member ONLY_SERIALIZE test objects are only ever read
(via to_json), never mutated, so mark them const per clang-tidy.

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

* Fix derived-type macro dispatch capping members at 62 instead of 63

NLOHMANN_JSON_GET_MACRO resolves 64 positional arguments, with NAME at
position 65. NLOHMANN_JSON_TYPE_TAG dispatches on Type plus the member
list, so it resolves correctly up to the 63 members NLOHMANN_JSON_PASTE
supports. NLOHMANN_JSON_DERIVED_TYPE_TAG dispatched on the two-token
Type,BaseType prefix plus the member list, running out one slot early:
at 63 members, position 65 landed on the last member name instead of a
sentinel and NLOHMANN_JSON_CAT built an undefined identifier such as
NLOHMANN_JSON_DEFINE_DERIVED_TYPE_INTRUSIVE_m63, with the compiler
reporting "unknown type name 'm1'" once per member and nothing pointing
at an argument-count limit.

That silently reduced all six NLOHMANN_DEFINE_DERIVED_TYPE_* macros from
63 members to 62, contradicting the "up to 63 members" contract in
docs/mkdocs/docs/api/macros/nlohmann_define_derived_type.md.

Drop the leading Type and defer to NLOHMANN_JSON_TYPE_TAG so the tag is
computed from BaseType plus the member list, which fits the available
slots. The zero-own-member derived bodies are therefore selected by tag
1 rather than 2, and the sentinel table for the derived tag is no longer
needed.

Add a regression test at the documented maximum for both the plain and
the derived macros; it fails to compile against the previous dispatch.

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

* Name the zero-member macro bodies by intent, not argument count

The dispatch tag was the literal token 1 or N, pasted onto a macro prefix
to select the zero-member or member-carrying body. For the derived-type
macros that reads wrong: their tag is computed after dropping the leading
Type, so the zero-member body was named _1 while taking two parameters
(Type, BaseType).

Emit EMPTY and MEMBERS instead. The mechanism is unchanged -- the tag is
still a token pasted onto the prefix by NLOHMANN_JSON_CAT -- but the body
names now say what they are rather than encoding an argument count that
only lines up for half of the macros.

Collapse the four duplicated zero-member bodies while here: with no
members there is nothing to default, so each _WITH_DEFAULT_EMPTY body was
a byte-for-byte copy of its plain counterpart. They are now one-line
aliases, leaving a single definition of what an empty object serializes
to per intrusive/non-intrusive and base/derived combination.

No functional change: for both zero-member and member-carrying types the
preprocessed to_json/from_json output is token-for-token identical, and
the arity limits are unchanged (63 members, base and derived).

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

* Document zero-member support in the macro API reference

docs/mkdocs/docs/features/arbitrary_types.md already gained a note, but
the three api/macros pages are where the parameter contract is actually
specified and they still described member as a non-empty list.

State that the list may be empty on each page, and add a note showing
what the zero-member case generates: an empty JSON object for the plain
macros, and base-type-only serialization for the derived ones. Both notes
record that the WITH_NAMES variants do not support this.

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

* Keep user macros named EMPTY or MEMBERS out of the member-count dispatch

The dispatch produced the bare token EMPTY or MEMBERS and pasted it onto
the macro prefix afterwards. In between, the token was rescanned, so a
user macro with either name replaced it: with `#define MEMBERS x` in
scope, even NLOHMANN_DEFINE_TYPE_INTRUSIVE(A, member) -- which compiled
before -- expanded to garbage, and `#define EMPTY` broke the zero-member
form.

Paste the suffix onto the prefix directly in the GET_MACRO slot table
instead. Operands of ## are not macro-expanded, so the selected body name
is formed before any user macro can interfere. NLOHMANN_JSON_TYPE_TAG and
NLOHMANN_JSON_DERIVED_TYPE_TAG become NLOHMANN_JSON_TYPE_BODY and
NLOHMANN_JSON_DERIVED_TYPE_BODY, taking the prefix as their first
argument; NLOHMANN_JSON_CAT is no longer needed. The body macro names are
unchanged, and so is the generated code.

Add a regression test that defines EMPTY and MEMBERS around plain and
derived types, with and without members.

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

* Test for EMPTY and MEMBERS so -Wunused-macros accepts them

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 20:44:30 +02:00
Alexander LaninandNiels Lohmann 465407f3ce Improve error message for const fields (#2818)
* Improve error message for const fields

* Reject const arguments to get_to() with a clear message

Reword the static_assert, add it to the C array overload of get_to() as well,
and document that v must not be const.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 18:02:38 +02:00
Niels Lohmann 02dd3e67f2 Fix stack overflow and exponential runtime when comparing nested values (#5390)
* Compare values without recursing, and without comparing them twice

Comparing two values compared their containers, which compare their elements,
which brought the comparison back once per nesting level. Two values nested
deeply enough exhausted the call stack and terminated the process with a
segmentation fault - the same bug as #5387, in the last operation that still
had it.

Worse, an ordered comparison took exponentially long in the nesting depth
before C++20. std::vector's operator< is a lexicographical comparison, which
asks whether an element is less than its counterpart and then whether the
counterpart is less than it - two full comparisons of everything below that
element, at every level. Comparing two equal values nested 30 levels deep,
which is nothing unusual, took 3.8 seconds; 40 levels would have taken an
hour, and nothing about the value has to be pathological to get there. C++20
is unaffected: std::lexicographical_compare_three_way asks once.

Compare a value that is nested too deeply to descend into on an explicit
stack instead, in a single pass that yields less, equal, greater or unordered
at once. Equality and the three-way comparison descend as they always did for
the first 128 levels, which nothing measurable costs them; an ordered
comparison no longer descends at all, which is what takes the exponent out of
it. Objects and arrays that are not nested deeply are otherwise compared
exactly as before.

The results are unchanged for every pair of values: 68121 comparisons of a
corpus that covers NaN, discarded values, mixed number types, binary values,
empty containers and both object types are identical to develop, in C++11,
C++17 and C++20, with and without thread_local storage and legacy discarded
comparison. Reproducing that meant reproducing two subtleties: a lexicographic
comparison steps over a pair it cannot order, where a three-way comparison
stops at it, and an object compares its keys with < where its entries are
ordered but with == where they are only checked for equality - not with the
object's own comparator, which for nlohmann::ordered_map tells equality.

Equality needs no ordering, so it no longer asks for any: a key or string type
that can only be compared for equality still works.

Measured (medians of 7 interleaved runs, clang -O3, C++11): comparing two
equal values nested 30 levels deep 3778 ms -> 0.002 ms; ordering flat objects
-33.6%; ordering flat arrays of numbers +27.3%, the one shape that pays for
the single pass; equality unchanged throughout.

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

* Describe comparison in the no-thread-local docs and CI target

Comparing two values now bounds its descent with a thread_local counter
just as copying does, so the JSON_NO_THREAD_LOCAL page, the macro
overview and the ci_test_no_thread_local target cover both rather than
copying alone.

Also record what switching the macro on costs a comparison: on the
benchmark documents, comparing two equal values takes 10% to 90% longer.

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

* Take the descent flag as an argument rather than testing it

MSVC reports the test of a constant as C4127 ("conditional expression is
constant"), which the Windows builds treat as an error: may_descend is
false for operator<, so the operand short-circuits the whole condition.

Passing it to compare_descent_exhausted() puts the test where the value
is an ordinary parameter, and leaves the call sites with no condition of
their own.

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

* Note the comparison fallback in the no-thread-local documentation

The macro page describes what the library defines JSON_NO_THREAD_LOCAL for
by itself in terms of copying alone; comparing falls back the same way.

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

* Parenthesise the reserve() computation in the comparison test

clang-tidy reports the mixed * and + as readability-math-missing-
parentheses, as it does for the identical line in the copy test.

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

* Use the shared descent bookkeeping rather than a second set

Comparing kept a thread_local count, a limit and a guard of its own beside
the ones copying already had, all three the same thing under a different
name. They are gone; the shared count, limit and guard do the work.

The guard grows a second constructor here, because the comparison
operators are written as a macro and a macro cannot use the preprocessor:
it cannot look the count up behind an #ifdef the way copy_structured does,
so the guard looks it up for it. nesting_depth_exhausted() arrives for the
same reason - whether an operator descends at all is a constant at every
call site, and testing it there is what MSVC reports as C4127.

Also say in compare_leaves what happens to a pair that is an array on one
side and an object on the other, since the answer is not obvious from the
code: an operator only descends into two values of the same type, so such
a pair is told apart by its types alone - unequal, and ordered the way the
types are - exactly as it is above the bound.

And record what the explicit stack costs: the comparison operators are
noexcept and the container comparison this replaces allocated nothing, so
running out of memory here ends the process instead of throwing. It takes
a value nested past the bound and an exhausted heap to reach, and the same
comparison used to exhaust the call stack, but it is a new way to fail.

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

* Amalgamate

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 17:58:59 +02:00
Niels Lohmann abbe52d6de Add JSON_PRECISE_STREAM_POSITION to leave the character that terminates a number in the stream (#5344)
* docs: qualify the operator>> stream positioning guarantee

operator>>'s notes state that it leaves the stream positioned right
after the parsed value, so that concatenated JSON values can be read
back to back. That does not hold when the value is a number: a number
is only terminated by the character that follows it, and the lexer's
unget() is simulated (it rewinds only the lexer's own bookkeeping),
so that character stays consumed from the stream.

Document the actual behaviour: the guarantee holds for all value types
except numbers, which must be followed by whitespace. Also qualify the
cross-reference on the JSON Lines page, which repeated the unqualified
claim.

Documentation only; the behaviour itself is tracked in #5340.

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

* fix: restore the character that terminates a number (#5340)

operator>> is documented to leave the stream positioned right after the
parsed value, so that concatenated JSON values can be read back to back.
That did not hold for numbers: a number is only terminated by the
character following it, and lexer::scan_number() reads that character
and calls unget() -- which is simulated and rewinds only the lexer's own
bookkeeping. input_stream_adapter consumes via sbumpc() with no matching
sungetc(), so the terminating character stayed consumed and the next
extraction started one byte too late ('1true' left the stream at 'rue').

Propagating unget() to the adapter directly does not work: next_unget
makes the following get() replay the cached character, so the terminator
would be delivered twice. Instead, restore the still-pending character
once at the end of a non-strict parse, where the input is handed back to
the caller:

- input_stream_adapter gains unget_character() (sungetc()) and advertises
  it via supports_unget, detected the same way as supports_seek.
- lexer::restore_pending_unget() turns a pending simulated unget of a
  real (non-EOF) character into a real one and clears next_unget so the
  character is not also replayed. It is a no-op for adapters that cannot
  unget, and reports failure when sungetc() fails, in which case the
  input is left as it was before.
- parser calls it on the three non-strict paths, i.e. for operator>> and
  sax_parse(strict = false).

Strict parse()/accept() are unaffected: they require the input to end
after the value, so the character is consumed by the end-of-input check
anyway. Parse error messages and reported positions are unchanged.

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

* tests: fix CI failures in the #5340 test helpers

Four CI failures, all in the new test code:

- GCC (-Werror=useless-cast): drop the `json(...)` wrapper around
  `json::parse(...)`, which already returns a `json`.
- GCC (-Werror=unused-result): assign the discarded `json::parse()`
  result to a dummy, the idiom used elsewhere in the test suite, and
  catch `json::parse_error&` for consistency.
- clang-tidy (google-default-arguments): remove the default argument
  from the `pbackfail()` override; `sungetc()` supplies the base
  declaration's default.
- MSVC (bad allocation): `no_putback_streambuf::underflow()` set a
  one-character get area without advancing `m_pos`, so an implementation
  whose `istream::get` peeks before it bumps re-read the same character
  forever. Keep no get area at all: `underflow()` peeks, `uflow()`
  consumes, and `sungetc()` still always lands in `pbackfail()`, which
  is what the test needs.

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

* fix: leave the character that terminates a number in the input

Read the character following a number without consuming it, instead of
consuming it and putting it back. input_stream_adapter now peeks with
sgetc() and only steps over the character when the next one is requested
or when the adapter is destroyed, so releasing it cannot fail - no
putback position is required from the streambuf.

Suggested by gregmarr in #5344.

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

* docs: match the version history wording to the peek-based fix

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

* docs: drop the whitespace-separator caveat from the parsing pages

The caveat added in #5343 describes the behavior this branch fixes: a
number no longer consumes the character that terminates it, so
concatenated values need no separator.

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

* refactor: split the strict and non-strict paths in parser

Folding the release_lookahead() call into the existing strict check left
the "in strict mode" comment on an else-if branch, and made the strict
condition in sax_parse() redundant with the branch it followed.

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

* Put the stream position fix behind JSON_PRECISE_STREAM_POSITION

Leaving the character that terminates a number in the stream is observable:
reading "1,2,3" with repeated operator>> works today only because the comma
after each number is swallowed, and std::getline after a number skips the
line break. Both break with the fix, so make it opt-in for 3.x, as suggested
by @gregmarr in the review.

- JSON_PRECISE_STREAM_POSITION (default 0) selects the peek-based
  input_stream_adapter. Without it, the adapter is the consuming one from
  develop and has no supports_lookahead, so lexer::release_lookahead() and
  the parser's calls to it compile to nothing.
- The macro changes input_stream_adapter's layout and member functions, so
  it gets the ABI tag _psp, after _bics. The ABI config tests, the natvis
  generator, and nlohmann_json.natvis (regenerated) know the tag.
- The tests for the fix move to unit-precise-stream-position.cpp, which
  defines the macro itself and runs in every build, and gain the two cases
  above. unit-deserialization.cpp pins the default behavior instead.
- The docs describe the default behavior again and point to the new macro
  page; version history says "added in 3.13.0, planned default in 4.0.0".

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 17:56:18 +02:00
Niels Lohmann 01b53c8c15 Keep JSON_DIAGNOSTICS parent pointers of ordered_json members after erase() and update() (#5552)
* Keep JSON_DIAGNOSTICS parent pointers of ordered_json members after erase() and update()

ordered_json stores its members in a vector, and two operations moved
members without restoring their parent pointers afterwards:

- ordered_map::erase() re-constructs every member after the erased one in
  place. The basic_json move constructor leaves m_parent at nullptr, and
  none of the object branches of basic_json::erase() (by key, iterator, or
  iterator range) called set_parents(). This also affected merge_patch()
  with a null member and patch() with a remove operation.
- update() only set the parent pointer of the inserted member. Adding a key
  can reallocate the vector, which copies all other members and leaves
  their m_parent at nullptr. The set_parents() call added for #4813 only
  repaired this for the nested object of a merge, not for the target.

The next assert_invariant() on such an object (for instance, when copying
it) aborted, and diagnostic messages lost the path prefix above the moved
member. std::map-based json was not affected, because its nodes do not
move.

Erasing from an ordered_map object now calls set_parents(), and update()
uses set_parent(), which already refreshes all members for vector-based
objects. This makes the #4813 workaround redundant.

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

* Account for JSON_DIAGNOSTIC_POSITIONS in the ordered_json parent-pointer test

The merge_patch() case parses its input, so with JSON_DIAGNOSTIC_POSITIONS
the exception message also carries the byte range of the parsed value.

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

* Silence clang-tidy for the intentional copy in the ordered_json parent-pointer test

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

* Keep parent pointers when update() merges past its descent bound

The iterative path of update() only set the parent pointer of the member
it inserted, like the recursive one did before. It now uses set_parent()
too, so ordered_json members that move when a nested object grows keep
their parents, and the set_parents() calls that patched this up after
each nested merge are gone.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-25 08:29:36 +02:00
Niels Lohmann 4daca40d7b Merge deeply nested objects without recursing per nesting level (#5547)
* Merge deeply nested objects without recursing per nesting level

merge_patch() and update(j, true) merged a nested object by calling
themselves on it, once per nesting level. A value nested deeply enough -
50,000 levels of objects on an 8 MiB stack - exhausted the call stack
and terminated the process, although parse() accepts such values without
complaint.

Bound the descent the same way dump() does. The recursion now carries
the nesting level, and once merge_depth_limit() (128) levels have been
entered, update_members_iteratively() and merge_patch_iteratively()
finish the merge on an explicit stack. They still merge a nested object
completely before the next member, and in the same order, so the results,
including the parents JSON_DIAGNOSTICS reports paths from, are unchanged.
Values nested less deeply than the bound run the same code as before, so
the common case does not pay for the stack: merging only on it cost
10-14% in a first version.

The public signatures are unchanged. The recursive worker behind
merge_patch() has its own name rather than being a private overload, so
that &basic_json::merge_patch stays unambiguous.

Tests check every depth up to 300 against recursive reference
implementations of both operations, check the diagnostic paths past the
bound, and merge objects nested 100,000 levels deep.

Fixes #5545 for update(j, true), and #5393 for merge_patch().

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

* Use the shared recursion limit in update() and merge_patch()

merge_depth_limit() is gone in favor of detail::recursion_depth_limit().
The two identical function-local frame structs become one member struct,
merge_frame, with a constructor, so both loops emplace_back() their
frames. merge_patch_iteratively() copies the frame it works on out of the
stack and changes it only through stack.back().

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

* Build the update()/merge_patch() diagnostics test values instead of parsing them

Parsed values carry byte positions under JSON_DIAGNOSTIC_POSITIONS, which
the expected messages do not include.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-24 17:12:03 +02:00
Niels Lohmann 7c90ec2323 Hash deeply nested values without recursing per nesting level (#5546)
* Hash deeply nested values without recursing per nesting level

std::hash<basic_json> hashed an array or object by hashing each element,
which called detail::hash again once per nesting level. A value nested
deeply enough - 50,000 levels of objects on an 8 MiB stack - exhausted
the call stack and terminated the process. parse() accepts such values
without complaint, since the parser is iterative, and a parsed value is
hashed wherever it is used as a key in an unordered container.

Bound the descent the same way dump() does: detail::hash takes the
nesting level, and once hash_depth_limit() (128) levels have been entered,
hash_iteratively() hashes what is left on an explicit stack. It combines
the seeds in exactly the same order, so hash values are unchanged. A value
nested less deeply than the bound is hashed by the same code as before,
without allocating, and is as fast as before.

Tests check that every depth up to twice the bound hashes exactly like
the recursive definition of the hash, and that values nested 100,000
levels deep hash without crashing.

Fixes #5545 for std::hash.

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

* Declare hash_frame's constructor noexcept

GCC's -Wnoexcept (an error in CI) flags the emplace_back() into the
hash stack under C++26: the constructor cannot throw, since cbegin() is
noexcept, but it did not say so. dump_frame's constructor is noexcept
for the same reason.

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

* Share one recursion depth limit, and copy the hash frame out of the stack

dump() and hash() each defined their own limit on how many nesting levels
they recurse into, and the operations still to come would have added more,
free to diverge over time. They now all use detail::recursion_depth_limit(),
in a header of its own; serializer::dump_depth_limit() and
hash_depth_limit() are gone.

hash_iteratively() now copies the frame it works on out of the stack and
changes the frame only through stack.back(), so nothing can refer into
the stack after entering an element has grown it.

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

* Parenthesize multiplications in the hash test for clang-tidy

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-24 17:12:02 +02:00
Niels Lohmann 2e91641de2 Test JSON_BRACE_INIT_COPY_SEMANTICS for real, and fix one-element tuples under it (#5544)
* Test JSON_BRACE_INIT_COPY_SEMANTICS for real, and fix one-element tuples under it

The opt-in JSON_BRACE_INIT_COPY_SEMANTICS was never exercised by CI:

- Its only test, in unit-regression3.cpp, was guarded by
  `#if defined(JSON_BRACE_INIT_COPY_SEMANTICS)` after the #include. The
  header #undefs the macro unconditionally in macro_unscope.hpp, so the
  guard was always false and the test compiled to nothing, whatever -D
  flag was passed.
- The ci_test_brace_init_copy_semantics target that passes the flag was
  not named by any workflow.

Move the test into its own translation unit that defines the macro before
including the header, as unit-diagnostics.cpp does for JSON_DIAGNOSTICS.
It now runs in every CI job and for every standard. Remove the unused
target: it ran the whole suite with the macro, and that suite deliberately
relies on default brace-init semantics in about 90 places
(e.g. `json({1})` meaning `[1]`), so it could never pass.

Running the whole suite with the macro did find one library bug:
to_json for std::tuple builds `j = { std::get<Idx>(t)... }`, so with copy
semantics a one-element tuple became its element. `json(std::tuple<int>{5})`
was `5` instead of `[5]`, and `get<std::tuple<int>>()` threw type_error.302
on the result. Under the macro, a one-element tuple now builds exactly what
the default deduction builds. Without the macro nothing changes.

The new tests also pin that the library's other conversions produce the
same values with and without the macro. The macro page now says that the
macro affects every single-element list (`json j = {1}` is `1`), and that
all translation units must agree on it, since it has no ABI tag.

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

* Make JSON_BRACE_INIT_COPY_SEMANTICS part of the ABI tag

The macro changes the body of the initializer-list constructor and adds a
to_json_tuple_impl overload, both with the same mangled names in either
mode, so mixing translation units silently picked one definition. Encode
it in the inline namespace as `_bics`, as JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
does with `_ldvcmp`. The macro is new in the unreleased 3.13.0, so no
existing namespace name changes.

- Move the macro's default into abi_macros.hpp so json_fwd.hpp computes
  the same namespace, and keep it defined under JSON_TEST_KEEP_MACROS.
- Check the tag in the ABI config tests and in the unit test.
- List `_bics` (and the missing `_dp`) in the namespace docs and in the
  natvis generator; regenerate nlohmann_json.natvis.
- Replace the "define it consistently" warning with an ABI note.

Suggested by @gregmarr in the review of #5544.

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

* Fix the cppcheck, clang-tidy and legacy-comparison CI failures

- to_json_tuple_impl() moved the element in both branches of a ternary;
  only one runs, but cppcheck reported accessMoved. Use if/else.
- The ABI tag test looked for "json_abi_bics", which misses when another
  tag comes first, as in json_abi_ldvcmp_bics; look for "_bics".
- readability-qualified-auto in the items() test.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-24 17:05:37 +02:00
Niels Lohmann 8699de3064 Stop allocating the BJData excluded-marker list per container (#5555)
write_ubjson() built a std::vector of the eight markers BJData forbids as
the type of an optimized container - one heap allocation plus a linear
search for every array and object it wrote with use_type, even for plain
UBJSON output, where the list isn't consulted. The list was also spelled
out twice. A constexpr helper, is_bjdata_excluded_type_marker(), replaces
both.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-24 17:04:44 +02:00