Commit Graph
814 Commits
Author SHA1 Message Date
Niels Lohmann bbf9b69d38 Add an error_handler parameter to to_msgpack
The MessagePack spec allows ill-formed UTF-8 in a str, so the default stays
keep (also if JSON_STRICT_BINARY_UTF8 is enabled), but decoders such as
msgpack-python reject it by default. With the parameter, strict catches
such strings and replace/ignore sanitize them, the same way as for the
other binary writers and dump().

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-02 09:02:34 +02:00
Niels Lohmann cf55a6cb3a Merge #5741 and make keep the default error_handler of the binary writers
Merges claude/binary-utf8-roundtrip-5651, where the writers now only check
UTF-8 if JSON_STRICT_BINARY_UTF8 is enabled, and applies the same rule to
the error_handler parameter added here: to_cbor(), to_ubjson(),
to_bjdata(), and to_bson() default to error_handler_t::keep, the behavior
of 3.12.0, or to error_handler_t::strict if JSON_STRICT_BINARY_UTF8 is
enabled (detail::binary_writer_default_error_handler()). Passing a handler
explicitly always takes precedence.

- Conflicts in binary_writer.hpp resolved in favor of this branch's
  error_handler, which replaces #5741's check_text_utf8().
- Tests: the "default parameters" section checks that the default equals
  keep; unit-binary_utf8_strict.cpp checks that an explicit handler
  overrides the macro's default.
- Docs: signatures show keep; parameter, exception, and format pages
  describe keep as the default and the macro; the two 3.13.0 version
  history entries of each writer are merged into one.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-02 08:48:59 +02:00
Niels Lohmann 809ace26b3 Keep writing ill-formed UTF-8 unchanged unless JSON_STRICT_BINARY_UTF8 is set
Throwing type_error.316 from to_cbor(), to_ubjson(), to_bjdata(), and
to_bson() by default would break code that works with 3.12.0, for example
code that stores ISO 8859-1 in a string and only writes it to a binary
format. Following the plan for 4.0.0, the check is now opt-in via the new
macro JSON_STRICT_BINARY_UTF8 (default 0), which is planned to become the
default in 4.0.0:

- abi_macros.hpp: default 0 and ABI tag _sbu8; macro_unscope.hpp undefines
  it; CMake option JSON_StrictBinaryUTF8; ABI namespace tests updated.
- binary_writer: the four writers call check_text_utf8(), which checks
  only if the macro is enabled. BON8 always checks, MessagePack never.
- Tests: the strict checks move to unit-binary_utf8_strict.cpp, which
  defines the macro; the per-format tests now check that the default
  writes the bytes unchanged (from_X(to_X(j)) == j).
- Docs: new macro page, macro lists, CMake option, namespace tags, and the
  writer/format pages describe the default and the opt-in.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-02 08:45:32 +02:00
Niels Lohmann fff221c58b Add an error_handler parameter for UTF-8 to the binary readers and writers
Adds error_handler_t::keep (invalid UTF-8 sequences are left unchanged) as
a fourth error_handler_t value, and threads an error_handler parameter
through the binary writers and readers:

- to_cbor/to_ubjson/to_bjdata/to_bson gain a trailing error_handler
  parameter (default strict, matching their existing type_error.316
  behavior); keep writes a string value or object key's bytes as is
  instead of throwing, and replace/ignore sanitize it exactly like
  dump() would, including for the BSON length prefix. to_msgpack and
  to_bon8 are unchanged.
- from_cbor/from_msgpack/from_ubjson/from_bjdata/from_bson gain a
  trailing error_handler parameter (default keep, i.e. the lenient
  behavior every binary reader had in 3.12.0 and still has after
  #5741); strict checks every string value and object key and raises
  parse_error.113 for ill-formed UTF-8, honoring allow_exceptions;
  replace/ignore sanitize it like dump() would. from_bon8 is
  unchanged, since UTF-8 lead bytes are structural there.

dump()'s own keep support writes ill-formed bytes as is, even with
ensure_ascii, while still \u-escaping well-formed characters around
them as usual.

The UTF-8 validity check (is_valid_utf8) and the replace/ignore
sanitizing logic (sanitize_utf8) now live in string_utils.hpp, shared
by the serializer and the binary reader/writer; error_handler_t itself
moved to its own header (detail/output/error_handler.hpp) so that
string_utils.hpp does not need to depend on serializer.hpp.

See #5529 and #5741.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 08:43:15 +02:00
Niels Lohmann 92c729f657 Accept ill-formed UTF-8 in all binary readers again
RFC 8949 and the MessagePack/BSON/UBJSON/BJData specs leave UTF-8
well-formedness checking up to the decoder, so following #5529 the
binary readers are lenient by default again, as in release 3.12.0
(the reader-side check was added by #5185/#5531, not in any release);
reader-side validation becomes opt-in in a follow-up PR. The writers
stay strict and throw type_error.316 for ill-formed UTF-8. BON8 is
unchanged, since UTF-8 lead bytes are structural there.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 07:59:14 +02:00
Niels Lohmann f3e30fa5b7 Merge branch 'develop' into claude/binary-utf8-roundtrip-5651
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 07:44:29 +02:00
Niels Lohmann e5a89d671f Fix lint debt: enum-macro NOLINTs, doctest as SYSTEM, no-op analyzer (#5737)
* Drop stale LCOV_EXCL_LINE from the json_pointer out_of_range.410 throw

The comment said the size_type overflow check in array_index() is only
triggered on special platforms like 32-bit, and the throw was excluded
from coverage. On 64-bit platforms the check is true for SIZE_MAX
itself, and unit-json_pointer.cpp has asserted that case four times
since #5395, so the line is executed in the coverage job. Reword the
comment and remove the exclusion marker so the coverage report notices
if the tests stop reaching it.

Part of #5725

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

* Name all three C-array check aliases in the enum-macro NOLINTs

NLOHMANN_JSON_SERIALIZE_ENUM(_STRICT) suppressed the c-array warning
under modernize-avoid-c-arrays only, but clang-tidy emits the same
diagnostic under the aliases cppcoreguidelines-avoid-c-arrays and
hicpp-avoid-c-arrays too. Any user running those checks got a false
positive at every macro expansion, and our own tests needed a local
NOLINT at each call site to work around it.

Name all three aliases in the four macro comments instead, and drop
the now-redundant c-array names from the five test call-site NOLINTs.
Comment-only change; behavior, the public API, and the ABI do not
change. Ran make amalgamate.

Part of #5725

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

* Include doctest as a SYSTEM directory instead of disabling warnings for all tests

test_main added -Wno-deprecated and -Wno-float-equal as PUBLIC compile
options for every non-MSVC compiler, so they were applied to every
translation unit, library headers included, and silenced the CI
warnings meant to check the library's own -Wfloat-equal pragmas. The
only code that actually needed the suppression was the vendored
doctest.h, which was included as a normal (non-SYSTEM) directory.

Include thirdparty/doctest as SYSTEM for test_main, matching what
tests/abi/CMakeLists.txt already does, and drop the two suppressions
from both targets. Verified locally that unit-comparison,
unit-conversions and unit-constructor1 compile clean with
-Werror -Weverything and doctest as -isystem, and that CMake still
configures with JSON_BuildTests=ON.

Part of #5725

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

* Remove the no-op ci_clang_analyze target

ci_clang_analyze configured the build with the real compiler and only
then wrapped ninja with scan-build. scan-build intercepts compiles by
overriding CC/CXX, but build.ninja already had the compiler path baked
in from the configure step, so every run bypassed the analyzer: CI
logs show "No bugs found" after a normal build, never an analysis.
The job also used Debian's frozen clang-tools-14 rather than the
image's own clang, and CLANG_ANALYZER_CHECKS still named three
valist.* checkers that current clang merged into security.VAList.

ci_clang_tidy already runs every clang-analyzer-* check (via
.clang-tidy's "Checks: '*'") with warnings as errors, so nothing is
lost by removing the dead job. Delete ci_clang_analyze,
CLANG_ANALYZER_CHECKS and the SCAN_BUILD_TOOL lookup from
cmake/ci.cmake, drop it from the ubuntu.yml ci_static_analysis_clang
matrix, and drop the now-unused clang-tools apt package (iwyu stays
for ci_single_binaries). Reword quality_assurance.md and
assurance_case.md, which described the dead job as a working control,
to say the Clang Static Analyzer checks run through clang-tidy.

Verified that `cmake -DJSON_CI=ON` still configures cleanly and that
ci_clang_analyze no longer appears in the generated build or in any
CMake/workflow file.

Part of #5725

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

* Re-enable portability-template-virtual-member-function; remove redundant forwards

.clang-tidy disabled three checks "to get the CI going" (#4489,
2024-11-13): portability-template-virtual-member-function,
bugprone-use-after-move and its alias hicpp-invalid-access-moved.

portability-template-virtual-member-function only flagged
output_stream_adapter::write_character/write_characters; annotate
both with NOLINT and re-enable the check.

bugprone-use-after-move flagged several double forwards that have no
effect at runtime:
- from_json.hpp calls std::forward<BasicJsonType>(j).at(Idx) inside
  pack expansions; at() has no ref-qualified overloads and always
  returns an lvalue reference, so the forward is a no-op. Replace with
  plain j.at(Idx) in all four places.
- the move constructor forwards the whole object to its base class
  and then reads other's members. That is item 9 of #5724 (together
  with its cppcheck suppressions) and is left to that change.
- input_adapters.hpp forwards the container twice on purpose, so the
  begin/end iterator types match adapter_type; annotate with NOLINT
  and a comment instead of changing behavior.

The check still flags the move constructor (see above) and two sites
in at(KeyType&&) (both overloads, json.hpp, in the throw's
string_t(std::forward<KeyType>(key)) after
find(std::forward<KeyType>(key))). Open PR #5689 rewrites that hunk,
so bugprone-use-after-move (and hicpp-invalid-access-moved)
stay disabled for now, with a comment explaining why; re-enable them
once #5689 and the #5724 move-constructor change have landed.

Also resolve the portability-avoid-pragma-once TODO: single_include
never has #pragma once (amalgamate.py strips it) and every supported
compiler accepts it in include/, so keep it disabled with an
explanatory comment instead of a TODO. Fix the stale "json.hpp,
around line 1265" comment in unit-class_parser.cpp, which now points
at the move constructor's actual line.

Behavior, the public API and the ABI do not change. Verified with
clang-tidy 22.1.8 that portability-template-virtual-member-function
now reports nothing, that bugprone-use-after-move/
hicpp-invalid-access-moved report only the known at(KeyType&&) and
move-constructor sites, and that unit-custom-base-class, unit-constructor1,
unit-conversions, unit-element_access2, unit-class_parser and
unit-diagnostic-positions (JSON_DIAGNOSTIC_POSITIONS=1) compile
under ASan/UBSan and pass with the same assertion counts as before.
Ran make amalgamate.

Part of #5725

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

* Fix stale and malformed NOLINT comments

json_sax.hpp named "-warnings-as-errors" in the NOLINT list on the two
JSON_ASSERT(false) lines; that is the suffix clang-tidy appends to a
diagnostic tag under WarningsAsErrors, not a check name, and every
other JSON_ASSERT(false) omits it.

unit-capacity.cpp carried 30 "// NOLINT(misc-const-correctness)"
comments on "json j = ...;" declarations that are all used with
non-const members afterwards, so the check has nothing to report
there.

unit-constructor2.cpp used a blanket "// NOLINT: access after move is
OK here" on a use-after-move that hides every check on the line;
naming bugprone-use-after-move and hicpp-invalid-access-moved keeps
the intent once those checks are re-enabled (#5724).

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

#5725 item 10

* Remove stale .clang-tidy entries

-google-runtime-references disabled a check that neither clang-tidy
22.1.8 nor 23.1.2 lists under --list-checks -checks='*'; it was
removed upstream. The commented-out HeaderFilterRegex line has been
unused since the active HeaderFilterRegex was introduced in #2561
(2021).

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

#5725 item 11

* Remove the GCC C++20 -Wignored-attributes pragma in json.hpp

The pragma (added in #5164) claimed to work around the C++ modules
redefinition errors of #5103, but #5103 is about hard errors (e.g.
"redefinition of std::__is_constant_evaluated()", conflicting
std::integral_constant) that ignoring a warning cannot suppress; they
are traced to GCC PR 124430 and reproduce with <map> or <string>
instead of json.hpp too. A GCC 16.2 -std=gnu++20 -fmodules build
following #5103's repro steps still fails with the pragma in place,
and a build of all test TUs with GCC_CXXFLAGS (which enable
-Wignored-attributes) and the pragma removed produces no such
warning. The block only hid a warning class from GCC C++20 users
while suggesting #5103 was handled.

Overlaps #5610, whose hunks touch the closing half of this pragma to
insert the json_literals.hpp include.

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

#5725 item 9

* Fix stale doxygen comments hidden by the -Wdocumentation pragma

macro_scope.hpp ignores -Wdocumentation and -Wdocumentation-unknown-command
for the whole library, which also hides genuine documentation mistakes:

- detail::unescape() documented "@return unescaped string" but returns
  void and unescapes its argument in place; reworded to
  "@param[in,out] s string to unescape in place" and dropped the
  bogus @return.
- basic_json::get()'s copy-conversion overload wrote "converted to
  @tparam ValueType" inside @return, which Doxygen and Clang parse as
  a second, malformed @tparam; changed to "@a ValueType", matching the
  two other get() overloads a few lines above that already use it.

This narrows the gap the -Wdocumentation pragma needs to cover; fully
replacing the Doxygen-only commands it also hides (item 2c) is left
for after #5267.

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

#5725 item 2

* Fix -Wextra-semi-stmt at its actual source, not assert()

clang_flags.cmake blamed the global -Wno-extra-semi-stmt on assert(),
but assert() expands to an expression under glibc and libc++ and does
not trigger this warning. unit-assert_macro.cpp overrides JSON_ASSERT
with "{if (!(x)) ++assert_counter; }", a bare block followed by a
semicolon at every JSON_ASSERT(...) call site in the library; that
was the actual source of 151 of the 208 -Wextra-semi-stmt sites found
in a Clang 22 -Weverything sweep of the test suite with the flag
removed. Switched to the standard do/while(false) macro idiom, which
does not expand to a statement-plus-semicolon, and corrected the
comment to name the remaining source instead: vendored Doctest's
CAPTURE(x) shim, which already ends in a semicolon.

Verified with clang++ -Wextra-semi-stmt (plus the file's other CI
ignores) that unit-assert_macro.cpp now compiles without any
-Wextra-semi-stmt diagnostic.

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

#5725 item 8 (step 1 of 2; step 2 covers the CAPTURE() call sites)

* Drop the redundant semicolon from CAPTURE() call sites; remove -Wno-extra-semi-stmt

doctest_compatibility.h defines CAPTURE(x) as DOCTEST_CAPTURE(x); (with
a trailing semicolon baked into the macro), specifically so call sites
do not need to add one themselves; most of the ~267 call sites already
follow that convention. The remaining 64 call sites across 20 files
wrote "CAPTURE(x);" anyway, turning into a statement plus an empty
statement and triggering -Wextra-semi-stmt. Dropped the redundant
semicolon at each of those sites.

With item 6 having already made vendored Doctest a SYSTEM include, and
this the last known source of -Wextra-semi-stmt findings, removed the
flag from clang_flags.cmake entirely.

Verified with clang++ -Wextra-semi-stmt (plus the file's other CI
ignores) that all 20 touched files, plus a file with no CAPTURE() use
(unit-json_pointer.cpp), compile without any -Wextra-semi-stmt
diagnostic.

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

#5725 item 8 (step 2 of 2)

* Switch ci_static_analysis_clang off the frozen LLVM 22 dev image

ubuntu.yml pinned the clang-tidy/clang-tidy-sanitizer/single-binaries
job to silkeh/clang:dev, a tag last pushed 2026-02-18 that reports
"clang version 22.0.0 (...+20251015...)", a pre-release snapshot from
before the LLVM 22 release; the maintainer now updates dev-unstable,
22, and latest instead. Switched to silkeh/clang:22, matching the
other clang jobs on :latest.

Verified with clang-tidy 22.1.8 (the image's actual version) against
this repository's .clang-tidy and library headers what the release
image newly reports compared to :dev:

- readability-redundant-typename fires at ~250 sites across the
  _cpp20-relevant conversion/to_chars headers; the library targets
  C++11 and keeps the typenames, so the check is disabled in
  .clang-tidy, matching how the file already handles checks that
  don't fit a C++11 codebase.
- misc-anonymous-namespace-in-header fires on the two anonymous
  namespaces in from_json.hpp and to_json.hpp; added the alias to
  their existing NOLINT (cert-dcl59-cpp, fuchsia-header-anon-namespaces,
  google-build-namespaces).
- bugprone-std-namespace-modification fires on every addition to
  namespace std: the std::hash, std::formatter and std::swap
  overloads in json.hpp, and the std::tuple_size/std::tuple_element
  specializations in iteration_proxy.hpp (this last file is not named
  in #5725's item 5, found by actually running clang-tidy 22.1.8
  against the current tree). All six are legal, deliberate additions
  to namespace std (explicit/partial specializations of std types, or
  the pre-C++20 std::swap overload); annotated each with the check
  name next to its existing cert-dcl58-cpp NOLINT.
- modernize-avoid-c-style-cast reported nothing new.

Also added clang++-22/21, clang-tidy-22/21, g++-16 and gcov-16 to the
find_program search lists in ci.cmake so a local "maximal warnings"
configure prefers the current toolchain version over an older one on
PATH.

#5725 item 5

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

* Regenerate cmake/gcc_flags.cmake for GCC 16.2.0

GCC_CXXFLAGS was generated for GCC 15.1.0, but ci_test_gcc and
ci_test_gcc_cxx{11..26} now run in gcc:latest, currently GCC 16.2.0,
so the "maximal warnings" job was missing warnings introduced since
15.1.0 while carrying entries GCC 16 treats as duplicates or no-ops.

Regenerated with https://github.com/nlohmann/gcc_flags (patched
locally to not crash on an option whose "-x c++ <opt> -" probe fails
before it reads stdin, e.g. -Wabi=; the tool otherwise raises
BrokenPipeError instead of recording the option as an error) run
against g++ 16.2.0 in the official gcc:16 Docker image, keeping the
documented -Wno-* exclusions and the same alphabetical placement
scheme as before.

Also added three GCC 16 warnings the generator cannot discover on its
own because it only probes value ranges/lists it finds in the -Q
option name itself, not in the enum choices --help=warnings documents
separately:

- -Wbidi-chars=any, -Wleading-whitespace=spaces: manually verified
  these compile cleanly with g++ 16.2.0.
- -Wstrict-flex-arrays: deliberately NOT added, unlike the other two.
  Without -fstrict-flex-arrays (which the library does not enable, as
  it would change codegen for flexible array members), GCC prints
  "'-Wstrict-flex-arrays' is ignored when '-fstrict-flex-arrays' is
  not present" on every translation unit, and under our -Werror that
  note itself aborts the build. This differs from the harmless
  no-op warnings already kept in the file (-Whsa, -Wsynth,
  -Wunreachable-code, -Wunsafe-loop-optimizations), which emit
  nothing; #5725 item 7 named -Wstrict-flex-arrays as one of the
  flags GCC 16 adds, but did not anticipate this failure mode.

Verified: compiled the library header and a representative set of
test translation units (including ones touched by items 1, 3, 8, 9,
10 of this issue) with the regenerated GCC_CXXFLAGS plus -Werror
under g++ 16.2.0 at -std=c++11 through -std=c++26, with zero warnings;
ran the full local test suite (129/129 passing, unrelated to this
compiler) as a regression check. CI must still confirm the actual
ci_test_gcc / ci_test_standards_gcc targets end to end, since this was
verified with direct g++ invocations rather than through the CMake/
CXXFLAGS environment-variable plumbing in ci.cmake.

#5725 item 7

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

* Avoid std::basic_string<CharType> for non-character output_adapter CharType

output_adapter<CharType, StringType> defaulted StringType to
std::basic_string<CharType>, and (with JSON_NO_IO undefined) always
declared a std::basic_ostream<CharType>&-taking constructor. For
CharType with no non-deprecated std::char_traits specialization (only
std::uint8_t is ever used this way, by the binary writers), simply
naming either type - as an unused default template argument, or as an
unused, never-called constructor's parameter type - instantiates
std::char_traits<CharType> merely to name it, which some standard
libraries mark deprecated: with the library-wide -Wdocumentation
pragma (item 2's other half, left for a later commit) temporarily
removed, an Apple clang 21 / libc++ TU calling json::to_cbor(j, vec)
with std::vector<std::uint8_t>& got one -Wdeprecated-declarations
warning per binary writer at the old output_adapters.hpp:193.

Replaced the eager std::basic_string<CharType> / std::basic_ostream
<CharType> defaults with a bool-tagged partial specialization (not
std::conditional, which requires naming both branches' types up
front regardless of which is selected, reproducing the same warning)
that only ever names std::basic_string<CharType> / std::basic_ostream
<CharType> when CharType is actually one of char, wchar_t, char16_t,
char32_t, or (with __cpp_lib_char8_t) char8_t. For any other
CharType, output_adapter's StringType and ostream-constructor
parameter fall back to two distinct empty placeholder types, kept
distinct so the two constructor overloads do not collide into a
single redeclaration.

Public API / behavior: passing a std::basic_string<std::uint8_t>& or
std::basic_ostream<std::uint8_t>& directly to a binary writer's
output_adapter now fails to compile instead of compiling with a
deprecation warning; this was neither documented nor tested. All
documented uses (std::vector<CharType>, std::basic_ostream<CharType>
and StringType for character CharType) are unaffected.

Verified with Apple clang 21 / libc++, with the two -Wdocumentation*
"ignored" pragma lines in macro_scope.hpp temporarily removed and
-std=c++11/c++20 plus the project's -Weverything flag set: calling
to_cbor/to_msgpack/to_ubjson/to_bjdata/to_bson/to_bon8 on a
std::vector<std::uint8_t> now produces no char_traits<unsigned char>
(or any other) deprecation warning, while the char-based string- and
ostream-adapter paths, and a to_cbor/from_cbor round trip, still
compile and run correctly; also verified with GCC 16.2.0. Ran the
full local test suite, including the binary-format unit tests
(unit-cbor, unit-msgpack, unit-ubjson, unit-bjdata, unit-bson,
unit-bon8, unit-binary_writer_sinks, unit-binary_formats,
unit-custom-binary-type): 129/129 passing.

#5725 item 2 (step a)

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

* Remove the library-wide -Wdocumentation pragma; fix what it hid

macro_scope.hpp / macro_unscope.hpp pushed and popped a Clang
diagnostic region over the entire library that ignored -Wdocumentation
and -Wdocumentation-unknown-command. Removed both pragmas and fixed
every finding a full -Wdocumentation (which implies
-Wdocumentation-unknown-command and -Wdocumentation-deprecated-sync)
build reports, so the library now compiles clean under Clang's
documentation checks without a blanket suppression. Overlaps #5267,
which is still open and edits a nearby doc block (json.hpp's
get()/get_impl() @return, already fixed in the item 2 step (b) commit
of this branch); this commit does not touch that block again.

Unknown Doxygen alias commands (Doxyfile removed in #3071, so these
were never rendered by anything) rewritten as plain prose, keeping the
same information:
- @requirement REQ-JSON-01 / REQ-JSON-02 (iter_impl.hpp,
  json_reverse_iterator.hpp): now "This class satisfies the following
  concept requirements (REQ-JSON-0N):".
- @liveexample{prose,example-id} (three sites in json.hpp): kept the
  prose, dropped the command wrapper and the trailing example-id
  (docs/mkdocs/docs/examples/*.cpp still exist and are used directly
  by the rendered docs, not through this in-header alias) and
  unescaped the "\," commas that were only needed for the old alias's
  comma-separated argument syntax.
- @complexity X (json.hpp x4, json_pointer.hpp x2, serializer.hpp x1):
  now "Complexity: X".

Backslash sequences Clang's comment lexer tried to parse as commands,
escaped to render as literal backslashes:
- lexer.hpp get_codepoint(): two `\u` occurrences.
- binary_reader.hpp get_bson_cstr() / get_bson_cstr_bulk(): two
  `\x00` occurrences.
- serializer.hpp: three `\uXXXX` occurrences (constructor @param,
  append_codepoint_to_string_buffer() @brief, and the ensure_ascii
  member comment).

One finding remained after all of the above: Clang reports
"declaration is marked with '@deprecated' command but does not have a
deprecation attribute" on the deprecated sax_parse(span_input_adapter&&, ...)
overload, even though JSON_HEDLEY_DEPRECATED_FOR does expand to
__attribute__((deprecated(...))) for Clang. Several isolated
reproductions of this exact declaration shape - doc comment,
template<>, two stacked __attribute__ macros, an overload set sharing
the name - did not reproduce the warning, so this looks like a
Clang comment/declaration-association quirk specific to this overload
inside the much larger basic_json class template, not an actual
documentation defect. Rather than keep the pragma library-wide for one
Clang false positive, added a tightly scoped
-Wdocumentation-deprecated-sync push/pop around just that overload.

Verified with Apple clang 21 and the project's actual -Weverything
flag set (cmake/clang_flags.cmake) on the full header at -std=c++11
and -std=c++20: zero -Wdocumentation* diagnostics. Also compiled
clean with GCC 16.2.0 (the pragmas are already __clang__-gated, so
this only confirms no unrelated breakage). Ran make check-amalgamation
and the full local test suite: 129/129 passing.

#5725 item 2 (step c)

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

* Take the JSON value by const reference in the array and tuple from_json paths

Review feedback on #5737 (gregmarr): once the no-op std::forward calls
are gone, the forwarding references have no purpose. from_json_fn
passes the value as const BasicJsonType&, so these functions were only
ever instantiated with a const lvalue anyway.

The std::array, std::pair and std::tuple overloads of from_json and
their helpers now take const BasicJsonType& and pass j on unchanged.
Because the deduced BasicJsonType is now the plain type, tuple_type and
the static_assert name const BasicJsonType& explicitly, so the
reference checks are unchanged: get<std::tuple<const std::string&>>()
still works, and get<std::tuple<std::string&>>() still fails the same
static_assert. from_json_tuple_get_impl keeps its forwarding reference,
since tuple_type calls it through std::declval.

Behavior, the public API and the ABI do not change. unit-conversions,
unit-constructor1, unit-udt, unit-udt_macro, unit-regression1/2/3,
unit-deserialization, unit-noexcept, unit-items, unit-allocator,
unit-custom-object-type, unit-ordered_json2 and
unit-brace-init-copy-semantics pass at C++11, C++17 and C++20 with
unchanged assertion counts. Ran make amalgamate.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 07:37:47 +02:00
Niels Lohmann cff0a61369 Share DOM SAX position handling; fix stale parser and lexer comments (#5731)
* Share the diagnostic-position setter of the DOM SAX parsers

json_sax_dom_parser and json_sax_dom_callback_parser each had a private
copy of handle_diagnostic_positions_for_json_value(), identical except
for comments. Move the body into one static member function,
detail::diagnostic_positions::set_from_lexer(value, lexer), which both
classes call with their lexer pointer. basic_json befriends the new
struct (only when JSON_DIAGNOSTIC_POSITIONS is enabled), as the position
members are private.

The discarded case is reached through the callback parser, so the
LCOV_EXCL markers that only the dom parser's copy had are gone. The
NOLINT on the unreachable default case loses the stray
"-warnings-as-errors", which is not a check name.

The start-position setup in start_object()/start_array() is left alone,
as #5706 is editing the callback parser's versions.

Behavior, the public API and the ABI are unchanged.

Part of #5712

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

* Correct the parser comments on recursion and skip_to_state_evaluation

The class documentation called the parser a recursive descent parser,
but sax_parse_internal() is a loop that keeps the open containers on an
explicit stack. The comment at the end of an array and of an object
said the flag is set to false while the code below it sets it to true.
Describe what the code does instead.

Comments only; behavior, the public API and the ABI are unchanged.

Part of #5712

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

* Update the discard_number_values comments to the current number path

The comments explaining the accept() shortcut in convert_number() and
the member documentation still argued in terms of strtoull()/strtoll()
and errno, which #5283 replaced with convert_integer(), and pointed at
scan_number() instead of convert_number(). They also did not say that
scan_number_bulk_contiguous() converts integers itself, so the shortcut
is only reached for input without bulk access, with
JSON_DIAGNOSTIC_POSITIONS, or when the bulk scanner falls back.

Rewrite both comments to describe the digit-count check in front of
convert_integer(), keeping the 18-digit bound and the json_sax_acceptor
argument. The stale <cstdlib> comment is left for after #5616, which
edits that include block.

Comments only; behavior, the public API and the ABI are unchanged.

Part of #5712

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

* List the UTF-8 validators instead of calling the DFA the only one

The documentation of decode() called the Hoehrmann DFA the single
source of truth for UTF-8 validation. It is used only by the serializer
and by is_valid_utf8() (CBOR/MessagePack/BSON/UBJSON/BJData text
strings). The lexer's scan_string() switch, validate_one_utf8() /
valid_utf8_prefix() (bulk string scan, BON8 bulk path and BON8 writer)
and the BON8 byte path in get_bon8_string() check the RFC 3629 ranges
on their own.

Replace the sentence with a list of the four validators, what each is
used for, and a note that they must accept the same sequences. Sharing
code between them was considered and dropped: it would save a few lines
in a validator that is entangled with BON8 pushback, and #5677 is
editing the BON8 byte path.

Comments only; behavior, the public API and the ABI are unchanged.

Part of #5712

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

* Fix stale doc comments and include lists in the input headers

input_adapters.hpp included <memory> and <numeric> for the removed
shared_ptr-based adapter design but used neither; it called
(std::min) without including <algorithm>. json_sax.hpp used
std::numeric_limits without including <limits>. Also corrected
comments that no longer matched the code: input_stream_adapter does
not skip the input's BOM (the lexer's skip_bom() does), the
span_input_adapter comment named the no-longer-existing
input_buffer_adapter type, lexer::get_string() does not reset the
token, binary_reader's get_number() doc opened with /* instead of
/*! (so Doxygen skipped it) and omitted BON8 from its endianness
note, and the UBJSON-binary-types note did not mention that BJData
'B' arrays are read as binary.

Left out: the lgtm suppression on lexer.hpp's scan_number() (in
#5616's hunk) and the "-1 if unknown" wording in json_sax.hpp's
start_object/start_array docs (in draft #5267's hunk), per the
verdict's conflict list.

Part of #5712

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

* Deduplicate the strict-EOF/release_lookahead/error block in parser::parse()

json_sax_dom_callback_parser and json_sax_dom_parser branches of
parser::parse() ran the same ~25 lines after sax_parse_internal():
the strict-mode EOF check (raising parse_error.101 through the SAX
parser), release_lookahead() in non-strict mode, and mapping an
errored SAX parser to a discarded result. The two copies had already
drifted apart in formatting and in the second copy's "see above"
comment.

Add a private parse_dom(DomSax&, strict) member that runs this shared
sequence once and returns whether the SAX parser did not error; both
branches of parse() now only construct their DOM SAX parser, call
parse_dom(), and (for the callback parser) map a discarded top-level
value to null. sax_parse() is left untouched, since it only runs the
EOF check and release_lookahead() when sax_parse_internal() succeeded,
unlike parse(), which runs them unconditionally.

Behavior-preserving: same operations in the same order for both SAX
parser kinds. Verified with unit-class_parser (strict/non-strict,
callback and non-callback), unit-deserialization and
unit-disabled_exceptions (JSON_NOEXCEPTION), plus a clean
make amalgamate / make check-amalgamation diff.

Overlaps #5601, which touches the same lines.

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

#5712 item 2

* Share the code point to UTF-8 encoding between the wide-string helpers and the lexer

The 1/2/3/4-byte UTF-8 encoding ladder was written out by hand three
times: in wide_string_input_helper<..., 4>::fill_buffer() for a UTF-32
code point, in the UTF-16 helper for both a BMP code unit and a valid
surrogate pair, and in the lexer's \uXXXX/\uXXXX\uYYYY handling. The
copies had drifted: the UTF-32 helper masked the leading bits of each
byte (& 0x1Fu, & 0x0Fu, & 0x07u) where the others relied on the shift
alone, even though both give the same result for a code point that is
already known to be in range.

Add detail::encode_utf8(cp, out) in string_utils.hpp, a single encoder
that invokes a callable once per output byte, most significant byte
first. Use it in the three valid-code-point branches (UTF-32 code
points up to U+10FFFF, UTF-16 code units outside the surrogate range,
and valid UTF-16 surrogate pairs) and in the lexer's \u handling, where
out forwards to add(). The UTF-16 helper's deliberate pass-through of
malformed surrogate units and the UTF-32 helper's 0xFF sentinel for
code points above U+10FFFF are untouched, since neither reaches the new
helper.

Behavior-preserving: same bytes in the same order for every valid code
point, verified with unit-class_lexer, unit-class_parser,
unit-deserialization, unit-wstring and the non-test-data parts of
unit-unicode1..5 (ASan/UBSan, C++11/17/20), and an escape-heavy parse
microbenchmark that shows no change (about 73 ms either way, median of
3, 1M escape sequences). single_include/ regenerated with make
amalgamate; make check-amalgamation leaves a clean tree.

Overlaps #5704, which rewrites the wide_string_input_helper
specializations touched here.

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

#5712 item 6

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 07:32:32 +02:00
Niels Lohmann 3926fcaac3 Deduplicate serializer dump code; fix stale includes, docs, and lint (#5729)
* Share scalar serialization between dump_internal and dump_value

dump_value()'s cases for string, binary, boolean, number_integer,
number_unsigned, number_float, discarded and null were a byte-for-byte
copy of dump_internal()'s (added together in #5285 for the iterative
fallback path). Any future change to scalar output had to be made in
both places, or the recursive and depth-limited paths would silently
start producing different bytes.

Extract the shared cases into a private dump_scalar() and have both
dump_internal() and dump_value() call it. Output is unchanged: dump(),
dump(4), dump(-1,' ',true) and the replace/ignore error_handler_t
variants are byte-identical over the json_test_data corpus before and
after, and dump() throughput on a scalar-heavy document is unaffected.

Part of #5709

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

* Drop serializer.hpp's dependency on binary_writer.hpp

The only use of binary_writer in serializer.hpp was
binary_writer<BasicJsonType, char>::to_char_type() to write the
U+FFFD replacement character's three bytes. With CharType=char this
is an identity conversion, so the include of binary_writer.hpp (and
transitively binary_reader.hpp) pulled in a large, unrelated header
for a no-op call.

Write the three bytes directly instead. serializer.hpp compiles
standalone with -Wall -Wextra -Werror, with and without
-funsigned-char, and unit-serialization's error_handler_t::replace
cases (with and without ensure_ascii) still pass. Moving
binary_writer's to_char_type/to_msgpack_length to its private section
is left as an optional follow-up.

Part of #5709

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

* Fix stale #include lines in the output headers

output_adapters.hpp included <algorithm> and <iterator> for std::copy
and std::back_inserter, which have not been used there since #3569
(2022). serializer.hpp included <algorithm> for std::reverse (also
unused), <cmath> for labs/isnan/signbit (only std::isfinite is used)
and <utility> for std::move (nothing from <utility> is used there),
while using std::next without including <iterator> at all, relying on
getting it transitively through output_adapters.hpp's own stale
<iterator>.

Drop the unused includes, add <iterator> for std::next, and correct
the remaining include comments. Both headers still compile standalone
with -Wall -Wextra -Werror.

Part of #5709

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

* Remove JSON_HEDLEY_NON_NULL(2) from write_characters() overrides

output_vector_adapter, output_stream_adapter and output_string_adapter
declared their write_characters(const CharType*, std::size_t) override
JSON_HEDLEY_NON_NULL(2), but binary_writer legitimately calls it with
a null pointer and length 0 for an empty string or binary value; the
type-erased call path only stayed silent under UBSan because the
static callee at those call sites is the unattributed virtual base.
A nonnull attribute on a definition lets GCC and Clang assume the
parameter is non-null inside the function body even when the call is
virtual, so this was latent undefined behavior, not just style.

Drop the attribute from the three overrides and document the
(nullptr, 0) contract on output_adapter_protocol::write_characters.
unit-cbor, unit-msgpack, unit-bson and unit-bon8 (which all exercise
empty binary/string payloads through the stream and vector/string
adapters) pass under -fsanitize=address,undefined,nonnull-attribute.

Part of #5709

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

* Update stale serializer doc comments to match the current implementation

dump_internal()'s doc block still described the pre-#5285/#5449
implementation: an escape_string() function that does not exist
(the function is dump_escaped), integer conversion "implicitly via
operator<<" (dump_integer actually uses a digit-pair lookup table),
and floating-point conversion via "%g" (IEEE-754 types go through
to_chars, others through snprintf). dump_value()'s comment said
elements are pushed for dump_internal to walk, but it is
dump_iteratively() that walks the stack. dump_escaped(), dump_integer()
and dump_float() each said they write "to output stream @a o", which
has not been true since the writer moved to write_buffer.

Doc-only change; no behavior, API or ABI impact.

Part of #5709

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

* Merge duplicate byte-to-hex helper and drop stale '| 0' promotions

serializer::hex_bytes() and binary_writer::hex_byte() had identical
bodies. Keep one, detail::hex_byte() in string_utils.hpp, and use it
from both. Also drop the `| 0` at the two serializer call sites
(hex_bytes(byte | 0) and hex_bytes(s.back() | 0)): #3088 (7440786b8)
added it so that `ss << std::hex << (byte | 0)` printed a number
rather than a char with the old stringstream writer; the int result
just narrows back to uint8_t now, so it was a no-op.

Behavior is unchanged: unit-serialization, unit-bon8 (whose
type_error.316 messages exercise this code) and unit-diagnostics
pass, and both headers still compile standalone with -Werror.

Part of #5709

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

* Trim two stale lint suppressions in serializer.hpp

dump_integer()'s `auto buffer_ptr = number_buffer.begin();` carried
NOLINT entries for cppcoreguidelines-pro-type-vararg and hicpp-vararg,
left over from the snprintf-based implementation (#3088); there is no
variadic call on that line, so keep only the qualified-auto
suppressions it actually needs. remove_sign()'s assert checked
`x < 0 && x < (std::numeric_limits<number_integer_t>::max)()) `with a
NOLINT(misc-redundant-expression) to hide it; the second conjunct is
always true once x < 0, and has been since 6ce2f35ba (2019), so
reduce the assert to `x < 0` and drop the suppression instead of
masking it.

Both are documentation-only changes to assertions/suppressions, not
behavior. The to_chars.hpp `#if 0` branch this item also flagged is
left alone, next to draft PR #5634's pending hunk.

Part of #5709

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

* Move the Hoehrmann SPDX copyright line to string_utils.hpp

serializer.hpp carried the SPDX-FileCopyrightText line for Björn
Hoehrmann's UTF-8 decoder, but the decoder (decode() and the utf8d
table) has lived in string_utils.hpp since #5185 (d19f7f5dc);
serializer.hpp now only calls decode(). Move the copyright line to
where the code it covers actually is.

Part of #5709

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

* Stop calling std::localeconv() on every dump()

The serializer constructor snapshotted std::localeconv() into a
locale_chars member on every dump(), even though the only reader is
dump_float(number_float_t, std::false_type)'s snprintf path, taken
only for a number_float_t that is neither IEEE single nor double.
localeconv() is not required to be thread-safe with setlocale(), so
every dump() paid for and raced on a lookup that almost never mattered.

Remove locale_chars and the locale member. Right before the
thousands-separator/decimal-point fixups in the snprintf path, read
std::localeconv() into local thousands_sep/decimal_point variables
(null-checked, first byte only, as before) - the same way
lexer::get_decimal_point() already does since #5597. Output is
unchanged unless the locale changes during a single dump(); in that
case the fixups now match what snprintf just produced, instead of a
value snapshotted before the call.

Overlaps draft PR #5608, which touches the same constructor and
dump_float() lines to move this code into a new
dump_float_snprintf(); this lands the lookup change now as #5709 asks,
and #5608 can do the lookup inside dump_float_snprintf() when it
rebases.

Verification: the full json_test_data corpus (742 files, dump(),
dump(4) and dump(-1,' ',true)) is byte-identical to before the change
under the C locale. Added a test pinning the new per-conversion
lookup: it switches LC_NUMERIC mid-dump() (via a streambuf that
switches on its first write, after the serializer's write buffer has
been flushed once but before a later float is converted) and checks
the decimal point is still normalized using the locale active at
conversion time. On a platform where long double is IEEE-754 double
(e.g. 64-bit Arm), dump_float() takes the locale-independent
to_chars() path and the test is a no-op there; it is meaningful on a
platform where long double is extended precision (most x86 targets).

Part of #5709 item 3

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-01 07:31:42 +02:00
Niels Lohmann c261578431 Deduplicate binary reader/writer helpers and fix stale comments (#5730)
* Fix stale and missing comments in binary_writer

The doc block of write_number() ended up above the byte_swap() helpers
added in #5286, about 80 lines from the function. It was also a plain
comment that Doxygen skips, said "write a number to output input", and
left BON8 out of the big-endian formats. Move it back onto
write_number() as a /*! block and fix the text.

write_bson() documented "@pre j.type() == value_t::object", but it
throws type_error.317 for every other type, and to_bson() relies on
that. Document the exception instead.

Explain why the CBOR binary subtype is always written with a 0xD8..0xDB
head and never in the one-byte tag form: binary_reader with
cbor_tag_handler_t::store only keeps those heads as a subtype, so
switching to write_cbor_head() would break round trips for subtypes
0..23.

Also fix the grammar of the to_char_type comment. Comments only; no
change in behavior, API or ABI.

Part of #5710

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

* Merge the duplicated UBJSON/BJData integer marker ladders

write_number_with_ubjson_prefix() (unsigned and signed overloads) and
ubjson_prefix() (number_integer and number_unsigned cases) each picked
the UBJSON/BJData integer marker (i, U, I, u, l, m, L, M, H) with their
own independent if/else ladder, and the values beyond 64 bits were
handled by a second, tag-dispatched pair of ladders. An optimized
container announces the marker of its first element via ubjson_prefix()
and then writes every element through write_number_with_ubjson_prefix(),
so the two had to be kept in lockstep by hand across four call sites.

Replace all of that with one ubjson_integer_prefix() built on
value_in_range_of<T>, and one write_ubjson_integer_payload() that
writes the value (or, for 'H', the decimal digits) for a given marker.
write_number_with_ubjson_prefix() and ubjson_prefix() keep their
signatures and now just call these two helpers.

Behavior, the public API and the ABI are unchanged. Verified with a
new regression test covering scalars and $-optimized arrays/objects at
every int8/uint8/int16/uint16/int32/uint32/int64/uint64 boundary for
to_ubjson/to_bjdata (both use_size/use_type settings), and by diffing
to_ubjson/to_bjdata output before and after over the json_test_data
corpus (bit-identical).

Part of #5710

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

* Remove dead get_char parameters in binary_reader

The non-recursive rewrite of the binary readers (#5505, #5506, #5507)
left parse_cbor_internal()'s and parse_ubjson_internal()'s get_char
parameters dead: parse_cbor_internal() has one caller and it always
passes true, and parse_ubjson_internal() has one caller and it always
uses the true default. Both parameters, and the @param docs describing
the "reuse the last character" mode they used to select, no longer
correspond to anything.

Drop both parameters, initialise fetch/prefix unconditionally, and
update the two call sites in sax_parse(). parse_cbor_value()'s and
get_ubjson_string()'s own get_char parameters are unrelated and are
left alone; both still have a false caller.

Also delete a stray `@return whether a valid MessagePack value was
passed to the SAX parser` doxygen block that sits directly above
parse_msgpack_value()'s real doc comment, a leftover of the same
rewrite.

Behavior, the public API and the ABI are unchanged; these are private
members of detail::binary_reader. Verified by compiling with
-Wunused-parameter and running unit-cbor, unit-ubjson, unit-bjdata and
unit-msgpack (offline, against the stubbed test_data.hpp).

Part of #5711

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

* Share the IEEE half-precision decoder between CBOR and BJData

binary_reader had two ~45-line copies of the IEEE 754 half-precision
decoder: CBOR's case 0xF9 and BJData's case 'h'. Once formatting is
normalised, the two blocks were identical except for the byte order
used to assemble the 16-bit half (CBOR is big endian, BJData is little
endian). Any future change to half-float decoding had to be made and
kept in sync in both places.

Add one get_half_float(format, little_endian) helper that does the two
get()/unexpect_eof() reads, assembles the half in the requested byte
order, decodes it per RFC 8949 Appendix D, and calls sax->number_float.
Both cases now just call it with their byte order; the BJData case
keeps its bjdata-only guard.

Behavior, the public API and the ABI are unchanged. Verified with a
scratch probe comparing the old and new decoders bit-for-bit (NaN by
isnan()) over all 65536 wire byte pairs, in both formats, and by
running unit-cbor and unit-bjdata (offline, against the stubbed
test_data.hpp).

Part of #5711

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

* Deduplicate the MessagePack unsigned-integer writer ladder

The number_integer (non-negative branch) and number_unsigned cases in
write_msgpack() each held their own copy of the fixint/uint8/16/32/64
ladder, kept in lockstep only by a comment ("we used the code from the
value_t::number_unsigned case here"). Both copies mixed union members:
the signed copy compared number_unsigned but wrote number_integer, and
vice versa.

Extract write_msgpack_unsigned(std::uint64_t), mirroring how
write_cbor_head() already avoids the same duplication for CBOR, and
call it from both cases. Each case now reads only its own active
union member. Output bytes are unchanged for the default 64-bit
number types.

#5710 item 3

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

* Unify float marker selection and fix the long double compile error

Four formats picked between a float32 and float64 marker through four
different helper styles: dummy-argument overloads for CBOR and
MessagePack, an std::is_same template for BON8, and a runtime if-chain
on input_format_t for write_compact_float(). With number_float_t set
to long double, to_cbor, to_msgpack and to_ubjson failed inside the
library with "call to 'get_cbor_float_prefix' is ambiguous", while
to_bson kept working because write_bson_double() takes a plain double.

Change write_compact_float() to take the two marker bytes directly
(each of its three callers already knows them at compile time) instead
of an input_format_t it only forwarded, and delete the now-unused
get_cbor_float_prefix(), get_msgpack_float_prefix(),
get_bon8_float_prefix() and get_compact_float_prefix() helpers. Turn
the two get_ubjson_float_prefix() overloads into one template. Both
write_compact_float() and get_ubjson_float_prefix() now report an
unsupported number_float_t with a static_assert naming the requirement,
rather than an ambiguous-overload error; the assert lives in the
function body, not the class scope, so to_bson with long double is
unaffected.

Verified with a probe basic_json<..., long double>: to_bson still
compiles and round-trips, while to_cbor/to_msgpack/to_ubjson now fail
to compile with the new static_assert message.

This changes the text of an existing compile error for users with an
unsupported number_float_t (documented as a public-API-visible change
in #5710).

#5710 item 1

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

* Deduplicate the BJData ndarray writer's dtype dispatch and drop <map>

write_bjdata_ndarray() built a 12-entry std::map<string_t, CharType> on
every call just to translate the _ArrayType_ name to a dtype marker
(the only reason binary_writer.hpp included <map>), then mapped dtype
to C++ type twice more: once as a switch for the range-check pass and
once as a separate if/else chain for the write pass, with nothing
checking that the two agreed. The caller also ran three at() lookups,
and the callee called value.at(key) about ten more times for the same
three members.

Replace the map with bjdata_ndarray_type_marker(), a plain string
comparison chain (a C++11 constexpr function cannot contain a switch,
so this mirrors binary_reader's own static table style). Replace the
switch/if-chain pair with one write_bjdata_ndarray_elements() that
switches on dtype once and calls a per-type helper -
write_bjdata_ndarray_element<T>() for the eight integer dtypes and
write_bjdata_ndarray_float_element() for 'd' - with a dry_run flag
selecting the range check or the actual write, so the two passes can
no longer disagree on the type. _ArrayType_, _ArraySize_ and
_ArrayData_ are now looked up once into references, and the four
header marker bytes ('[', '$', '#') are written through to_char_type()
like the rest of the UBJSON/BJData writer.

The 'd' (single-precision) rule is left exactly as before, since #5707
is expected to change it separately.

Verified byte-for-byte identical output before/after for every dtype
(including the Draft 2/Draft 3 'byte' fallback and the use_count/
use_type combinations) via a standalone probe, plus round-tripping
through from_bjdata().

Overlaps #5707, which is expected to touch the 'd' dtype case, and
#5518, which is expected to move the write_bjdata_ndarray() call site.

#5710 item 4

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

* Assert that write_bson_document() consumes every calc_bson_sizes() entry

calc_bson_sizes() and write_bson_document() are a hand-synchronized
pair of passes over the same object/array tree, introduced by #5553:
the size pass appends to nested_sizes in visiting order, and the write
pass consumes the table by position with nested_sizes[next_size++].
Nothing checked that the write pass consumed the whole table. If a
future change touched only one of the two passes - for example to skip
or reject an entry - every later size prefix in the document would be
silently wrong.

Add JSON_ASSERT(next_size == nested_sizes.size()) where
write_bson_document() returns, so such a future drift between the two
passes is caught immediately (JSON_ASSERT expands to nothing in
release builds using assert(), and the fuzzers/tests already build
with it enabled). The two passes agree today, so this changes nothing
observable; it only guards against the risk described in #5710 item 5.

Extracting a shared stepper for the two passes (the second half of the
proposed change) is left for a follow-up: it only saves ~30 lines and
the issue asks for it only if the result reads clearly, which needs
more room to get right than a mechanical cleanup pass allows.

#5710 item 5

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

* Make the BJData lookup tables static functions instead of members

binary_reader held bjd_optimized_type_markers and bjd_types_map as
non-static const members (12 string_t objects for the type-name table),
built and destroyed on every from_cbor/from_msgpack/from_bson/
from_ubjson/from_bon8/from_bjdata call even though only from_bjdata
ever reads them. They also needed the #define/decltype/#undef
workaround from #3637 and two NOLINTNEXTLINE suppressions, and
binary_writer already carries the same two lists in another form
(is_bjdata_excluded_type_marker() and a local std::map in
write_bjdata_ndarray(), the latter removed by the item-4 commit), so
the excluded-marker lists could drift apart.

Replace bjd_optimized_type_markers with static constexpr
is_bjd_excluded_optimized_type(char_int_type), using the same ||-chain
as binary_writer's is_bjdata_excluded_type_marker(). Replace
bjd_types_map with a non-constexpr static bjd_type_name(char_int_type)
switch returning nullptr for an unknown marker (a C++11 constexpr
function cannot contain a switch). Delete both
JSON_BINARY_READER_MAKE_* macros, the bjd_type pair alias, the
NOLINTNEXTLINE suppressions, detail::make_array() (no longer used
anywhere), and the now-unused <algorithm> and <array> includes.

Update the two call sites (the ND-array excluded-type check and the
_ArrayType_ lookup) accordingly, and replace unit-bjdata.cpp's
"LUT arrays are sorted" section, which only checked the two tables'
internal ordering, with a check of all 12 type names and all 8
excluded markers against both new functions.

#5711 item 1

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

* Read CBOR's 1/2/4/8-byte argument through one helper

parse_cbor_internal() hand-wrote the same "read a 1/2/4/8-byte
big-endian unsigned integer" ladder four times over:
- twice for tag numbers 0xD8-0xDB, once in the tag_handler::ignore
  branch and once, nearly identically, in the ::store branch (~90
  lines to read one integer);
- twice more for container lengths, once for array heads 0x98-0x9B and
  once for map heads 0xB8-0xBB, where the 1/2-byte forms called
  enter_array()/enter_object() directly and the 4/8-byte forms
  additionally went through get_cbor_container_size().

Add get_cbor_argument(std::uint64_t&), reading the width selected by
current & 0x1F via the same get_number() calls as before (so EOF is
reported exactly as before), and route all four sites through it:
- 0xD8-0xDB now read the argument once per branch instead of switching
  on `current` a second time; behavior split cleanly from embedded tags
  0xC0-0xD7 (tag value in the head, no argument to read), which is now
  its own case block that no longer has to fall into the ::store
  switch's "default" case to reach the same tag_pending = true; return
  true; outcome.
- 0x98-0x9B and 0xB8-0xBB collapse into one case block each, always
  going through get_cbor_container_size() (harmless for 1/2-byte
  lengths, which already always fit).

Verified byte-for-byte identical behavior before/after with a
standalone probe covering embedded and multi-byte tags under all three
tag_handler_t settings, a tag over a byte string (subtype path),
truncated tag/length arguments of every width, and array/map lengths
of every width, including the out_of_range.408 "excessive size" case:
same exceptions, same messages, same chars_read, same successful
results.

Left the string/byte-string length ladders in get_cbor_string()/
get_cbor_binary() untouched, as noted in #5711 item 2, since #5325 is
expected to touch them separately.

Overlaps #5601 (adds a branch right above the embedded-tag case) and
#5607 (touches the integer cases 0x18-0x1B, which share this ladder's
shape in separate hunks).

#5711 item 2

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

* Add leave_container() to match enter_container()

Every container is opened through enter_container(), whose docs
promise that a check placed there runs before every start event. The
close side had no equivalent: the same
"container_stack.pop_back(); dispatch to end_object() or end_array()"
sequence was written out separately in BSON, CBOR, MessagePack,
UBJSON/BJData and BON8, each copying the pattern of keeping an
is_object flag around the pop_back() that would otherwise invalidate
a reference to it. A check needed on close would have had to be added
in five places, and a sixth copy could go unnoticed.

Add leave_container() next to enter_container(), doing the same
pop-then-dispatch, and replace the five sites with it. Each site keeps
its own surrounding logic (BSON's check_bson_document_size() call
before popping, MessagePack's is_object copy used again below,
UBJSON/BJData's remaining-container handling after popping, BON8's
top used again below); only the repeated pop/dispatch line pair is
now shared.

Verified all six binary-format unit suites and unit-regression2's
deep-nesting tests (dependent count/reuse count and the bjdata ndarray
depth cases) still pass, compiled with -Wall -Wextra and ASan/UBSan.

Overlaps #5601, which is expected to add a sixth close site in its own
skip loop; that site can route through leave_container() too once it
lands.

#5711 item 4

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

* Stop passing the input format to sax_parse() when the reader already has it

binary_reader's constructor stores the format in the input_format
member, and sax_parse(format, sax_, strict, tag_handler) took the same
value again purely to dispatch on it. Every in-tree caller passed the
same value both times (all 16 from_cbor/from_msgpack/from_ubjson/
from_bjdata/from_bon8/from_bson call sites in json.hpp, and the three
public basic_json::sax_parse() overloads), so nothing was broken
today, but a caller of the detail class directly (only reachable via
JSON_PRIVATE_UNLESS_TESTED, as unit-bjdata.cpp already does) could
pass a mismatched pair - say bjdata to the constructor and ubjson to
sax_parse - and dispatch on one format while applying the other
format's rules; the default-constructed input_format_t::json reader
would additionally hit JSON_ASSERT(false) in exception_message() on
its first error.

Add sax_parse(json_sax_t*, bool, cbor_tag_handler_t) forwarding to the
existing overload with the stored input_format, and switch every
caller to it: the 16 from_*() sites (keeping their
`// cppcheck-suppress[accessMoved]` comments) and the three
basic_json::sax_parse() overloads, all of which already had the format
available from their own `format` parameter. The four-argument overload
is kept for anyone still calling it, now with
JSON_ASSERT(format == input_format) so a mismatch fails immediately
in a debug build (assert-enabled binaries, including the fuzzers and
test suite) instead of misbehaving; verified with a probe that
constructs a reader for one format and calls the explicit overload
with another, which aborts on that assertion as expected.

Removing or asserting against the constructor's input_format_t::json
default, which would affect direct detail users, is left as a separate
decision per #5711 item 5.

Overlaps #5601, which is expected to add an AllowRecovery template
parameter to sax_parse() and touch these same call sites in json.hpp.

#5711 item 5

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

* Deduplicate UBJSON/BJData signed-count handling, drop dead ndarray checks

get_ubjson_size_value()'s 'i'/'I'/'l'/'L' cases each read a differently
sized signed integer and then repeated the same "reject negative with
error 113" check; only 'L' additionally checked value_in_range_of for
the out_of_range.408 case. Any change to that error path had to be
made four times.

Add get_ubjson_signed_count<SignedType>(std::size_t&), doing the read,
the negative check and the range check once, and route all four
markers through it. The range check is a no-op for 'i'/'I'/'l' (their
values always fit std::size_t) and only live for 'L' on a 32-bit
std::size_t target, matching today's behavior exactly.

In the ndarray dimension-product loop, the preceding loop already
returns early on any zero dimension and result starts at 1, so `i > 0`
in the pre-multiplication overflow check was always true, and
`result == 0` in the post-multiplication check could not be reached
either: two positive factors whose product does not overflow (as the
pre-check already guarantees) cannot be zero. Drop the dead `i > 0 &&`
and narrow the post-check to `result == npos`, the one case the
pre-check cannot rule out (an exact, non-overflowing match with the
sentinel reserved for unknown-size containers), with a comment
explaining why.

Verified byte-for-byte identical behavior before/after with a
standalone probe covering negative counts for every marker, a matching
positive count, and ndarray inputs, plus the full unit-ubjson and
unit-bjdata suites (same assertion counts as before this change).

Overlaps #5601 (rewrites the four parse_error calls and the overflow
checks touched here) and #5607/#5707 (touch neighboring lines in the
same functions).

#5711 item 6

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

* Drop redundant format parameter and dummy float argument (review)

binary_reader::sax_parse(format, ...) only ever had to equal the format
given to the constructor, which it asserted. With every caller already
on the format-less overload, remove the four-argument overload and
dispatch on the stored input_format directly. binary_reader is a
detail class, so this is not a public API change.

get_ubjson_float_prefix() took a value only to deduce its type; make
the type an explicit template argument instead.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 22:48:32 +02:00
Niels Lohmann 35802e78d6 Remove dead Makefile targets; document macro_builder; tidy serve_header (#5735)
* Remove dead doctest help entry and pretty_format target from Makefile

The top-level Makefile still carried three leftovers:

- The help text listed a "doctest" target that was removed in #4560,
  so "make doctest" fails with "No rule to make target". The example
  check now runs as "make check_output -C docs".
- "pretty_format" ran clang-format on all sources, but .clang-format
  was deleted in #4573, so the target reformatted everything in the
  default LLVM style, against the Artistic Style formatting that
  "make pretty" applies and CI enforces.
- "clean" removed benchmarks/files/numbers/*.json, a directory that no
  longer exists since the benchmarks moved to tests/benchmarks (#3462).

Only maintainer tooling changes; the library is not affected.

Part of #5717

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

* Document tools/macro_builder and tidy up serve_header.py

tools/macro_builder generates the NLOHMANN_JSON_EXPAND,
NLOHMANN_JSON_GET_MACRO and NLOHMANN_JSON_PASTE* macros in
macro_scope.hpp, but nothing referred to it. Add a README that explains
what it generates, how to run it and where the output goes, and which
dependent tables (NLOHMANN_JSON_DOUBLE_PASTE, NLOHMANN_JSON_TYPE_BODY)
are maintained by hand. Point to it from a comment above
NLOHMANN_JSON_EXPAND. The generator itself is unchanged; following the
README reproduces the header byte for byte.

In serve_header.py, drop the LGTM suppression (LGTM.com shut down in
2022), replace the """.""" placeholder docstrings with real ones, and
import socket and ssl at module level. DualStackServer.server_bind uses
socket, which was only imported under __main__; when the module was
imported instead, the NameError was swallowed and IPV6_V6ONLY was not
cleared.

The header change is a comment only; behavior, API and ABI are
unchanged.

Part of #5717

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

* Hash every release_files artifact, not a hardcoded subset

The `release` target signed and copied json_fwd.hpp into release_files
alongside json.hpp, but the shasum line that writes hashes.txt only
listed json.hpp, include.zip and json.tar.xz. Users could not verify
the published json_fwd.hpp against hashes.txt.

Hash every file in release_files except the .asc signatures instead
of naming files by hand, so a newly shipped header (such as the
json_literals.hpp that #5610 adds to this target) cannot be missed
again.

Only affects the generated hashes.txt release artifact; the library
itself is unaffected.

Overlaps #5610, which touches the same lines to add json_literals.hpp
to the release target.

#5717 item 1

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

* Remove the broken fuzz_testing* Makefile targets

fuzz_testing and fuzz_testing_{bon8,bson,cbor,msgpack,ubjson} seeded
fuzz-testing/testcases from tests/data, which was removed in dbf1a1f41
(2020) when the test data moved to the external json_test_data repo.
The find command found nothing, but the pipeline's exit status was
that of xargs, so the recipe still reported success with an empty
corpus, and the printed afl-fuzz command would refuse to start.

The recipes were also six near-identical copies with unquoted -name
patterns, used the legacy CXX=afl-clang++, and fuzzing-start/stop were
missing from both the help output and .PHONY. tests/fuzzing.md already
documents the working flow (download json_test_data, then
`make -C tests fuzzers`), so replace the six broken targets and their
help lines with a single pointer to that document instead of trying
to keep six copies of a fragile shell pipeline in sync.

This does not affect OSS-Fuzz, which builds through tests/Makefile.

Overlaps #5621, which adds a seventh copy of the same broken line for
fuzz_testing_json_view.

#5717 item 2

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

* Remove stale Travis comment above check-amalgamation

check-amalgamation carried "Note: this target is called by Travis",
left over from before the project switched off Travis CI. The prior
Makefile cleanup commit removed the other stale Travis-era leftovers
(the doctest help entry, pretty_format, and the benchmarks/ path in
clean) but missed this comment.

#5717 item 4

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

* Fix stale install/usage instructions in the vendored amalgamate README

tools/amalgamate/README.md is the unmodified upstream text and no
longer matches how the tool is used here:

- It named a Bitbucket origin that no longer exists; CHANGES.md
  already tracks the GitHub mirror commit this copy is based on.
- It asked for Python 2.7, but CI and the Makefile run the script
  with python3.
- It told readers to run ./test.sh (not vendored) and install to
  /usr/local/bin; in this repository the tool runs through
  `make amalgamate`.
- Its usage synopsis showed `-v` taking no argument, but the script's
  own argparser requires `choices=["yes", "no"]`, so that form fails
  with "argument -v/--verbose: expected one argument". The Makefile
  calls it as `--verbose=yes`.
- It pointed at test/source.c.json and test/include.h.json, which are
  not vendored; the configs actually used are config_json.json and
  config_json_fwd.json.

Rewrote only the Installing and Using sections to match; left the
"Here be dragons" caveats and the rest of the vendored code untouched
to avoid diverging further from upstream.

Overlaps #5615, which edits amalgamate.py, this README and CHANGES.md.

#5717 item 6

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

* Derive generate_natvis.py's ABI tag list and version from abi_macros.hpp

generate_natvis.py hard-coded abi_tags = ['_diag', '_ldvcmp', '_dp',
'_bics', '_psp', '_snul'] and required --version on the command line.
The source of truth is include/nlohmann/detail/abi_macros.hpp: the
NLOHMANN_JSON_ABI_TAG_* defines, the argument order of
NLOHMANN_JSON_ABI_TAGS_CONCAT, and NLOHMANN_JSON_VERSION_MAJOR/MINOR/
PATCH. Nothing checked that the copies stayed in sync, and they have
drifted apart before: _dp was added in #4517 but missed here until
#5544, and 3.11.3 shipped json_abi_v3_11_2 namespaces (#4340).

Parse the tag list (in NLOHMANN_JSON_ABI_TAGS_CONCAT order) and the
version from abi_macros.hpp instead of hard-coding them. Make
--version optional (falling back to the parsed version) and default
the output directory to the repository root the script lives in.

Add a "natvis" Makefile target that runs the script, and extend
check-amalgamation to regenerate nlohmann_json.natvis and fail on a
diff, the same way it already does for the amalgamated headers and
BUILD.bazel. Wire the same regeneration into check_amalgamation.yml,
using the tool copy checked out from develop (as the workflow already
does for amalgamate.py) and installing jinja2 from
tools/generate_natvis/requirements.txt. Update the tool's README to
say it must be re-run after adding an ABI tag or bumping the version.

Verified: a run against develop produces no diff (with either the
default or an explicit --version 3.12.0); adding a dummy
NLOHMANN_JSON_ABI_TAG_* without a matching #define makes the script
fail loudly instead of silently omitting the tag; xmllint --noout
passes on the regenerated file; and running the script from a
directory other than the one being checked (simulating the workflow's
separate tool checkout) against this repository root also produces no
diff.

Overlaps #5600, which added _ekmo to the same hand-written abi_tags
line and regenerated the file.

#5717 item 3

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

* Strip the leading "./" find(1) prefix from release hashes.txt entries

bc6e7db72 (#5717 item 1) switched the release target's shasum line from
naming files by hand to $$(find . -type f -not -name '*.asc' | sort),
so a newly shipped header is hashed automatically. Run from inside
release_files, that find prints paths as "./json.hpp" instead of
"json.hpp", so hashes.txt lists "./json.hpp" etc. instead of the plain
filenames it always used. shasum -c still verifies "./json.hpp" fine,
but it is a needless cosmetic regression for anyone reading the file
or matching it against release notes.

Strip the "./" prefix with sed before sorting, keeping the filenames
exactly as before while still hashing every artifact automatically.

Review fix for #5717 item 1 (PR #5735).

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

* Fix check_amalgamation.yml: pass --version to generate_natvis.py

bff45f111 (#5717 item 3) made --version optional in
tools/generate_natvis/generate_natvis.py and wired the workflow's new
"Regenerate nlohmann_json.natvis" step to call it without --version,
relying on the script deriving the version from abi_macros.hpp itself.

But NATVIS_TOOL_DIR is checked out from develop, the same way TOOL_DIR
already is for amalgamate.py, precisely so an in-flight PR's tooling
changes cannot mark themselves clean. Until this PR (or an equivalent)
merges to develop, that checkout is the old generate_natvis.py, whose
--version argument is still required=True. The new step's invocation
of "generate_natvis.py $MAIN_DIR" (no --version) then fails argparse
on this PR's own CI run with "the following arguments are required:
--version", before the check ever gets to compare output.

Extract the version from $MAIN_DIR's own abi_macros.hpp in the
workflow and always pass it as --version. That satisfies the old
script's required argument and is accepted as an explicit override by
the new one, so the step behaves the same whether NATVIS_TOOL_DIR holds
the pre- or post-merge tool, and stays correct for later PRs that bump
the version.

Verified by running the workflow step's shell logic locally against
both the pre-#5717 generate_natvis.py (checked out at 633de8e44) and
the new one: both produce the identical nlohmann_json.natvis as the
committed file.

Review fix for #5717 item 3 (PR #5735).

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

* Extend tools/macro_builder to also generate DOUBLE_PASTE and TYPE_BODY

tools/macro_builder only emitted NLOHMANN_JSON_EXPAND..PASTE64, so two
other tables that scale with the same max_args stayed hand-maintained
with nothing checking them: NLOHMANN_JSON_DOUBLE_PASTE (added by hand
in #4563 for the *_WITH_NAMES macros) and the 64-slot dispatch table of
NLOHMANN_JSON_TYPE_BODY (the #4041 zero-member/one-or-more-member
switch). Both tables pass one macro name per slot to the same
NLOHMANN_JSON_GET_MACRO dispatch as PASTE, so they can drift out of
sync with max_args exactly the way _dp did in the ABI tag list fixed
by #5544.

Extend main.cpp with build_double_paste_code() (same recursive-doubling
shape as build_paste_code(), but DOUBLE_PASTE consumes two arguments
per member, so an even slot index falls back to the next lower odd
DOUBLE_PASTE<N>) and build_type_body_table() (max_args - 1 MEMBERS
slots and one trailing EMPTY slot, 8 per line, matching how it is
written by hand today). Add a "type_body" argument that selects the
TYPE_BODY block, since it lives at a separate location in
macro_scope.hpp from the EXPAND..DOUBLE_PASTE63 block; plain invocation
is unchanged apart from covering the extended range. No longer emit
the tool's old trailing blank line, so its output is directly diffable
without post-processing.

Verified with c++ -std=c++11: running the tool (with and without
"type_body") and piping the raw output through the pinned astyle
reproduces both blocks of the current macro_scope.hpp byte for byte.
tests/src/unit-udt_macro.cpp (all NLOHMANN_DEFINE_TYPE_*/_WITH_NAMES/
zero-member variants) passes unchanged under -std=c++11 and -std=c++17
with -fsanitize=address,undefined.

Add a "macro_builder_check" Makefile target that builds main.cpp,
regenerates both blocks into a scratch directory inside the repository
(astyle's --project lookup needs the target files under the same tree
as .astylerc, unlike an external /tmp directory), and diffs them
against the corresponding ranges of macro_scope.hpp; wire it into
check-amalgamation next to the natvis check. Wire the same regeneration
into check_amalgamation.yml, splicing the (still unindented) generated
blocks back into the PR's own macro_scope.hpp before the existing
astyle/amalgamation step runs, so that step's own tree-wide astyle
pass both indents them and folds any drift into the amalgamation
patch/diff the workflow already produces.

Unlike amalgamate.py and generate_natvis.py, this step builds
tools/macro_builder/main.cpp from the pull request's own checkout
($MAIN_DIR) rather than a separate checkout of tools/ at develop: this
tool has no independent source of truth to regenerate against (its
README documents that it must reproduce macro_scope.hpp byte for
byte), so a develop-pinned copy would only reproduce the
generate_natvis.py trap fixed in a previous commit on this branch,
where a PR that teaches the tool to cover more of the file fails its
own CI until that PR merges and updates the develop copy.

Add tools/macro_builder/README.md documentation for both new tables
and the two-invocation usage, and a short pointer comment above
NLOHMANN_JSON_TYPE_BODY (the EXPAND pointer already covered the first
block; extended its wording to include DOUBLE_PASTE63).

Closes #5717 item 5 in full, completing what the documentation-only
"Document tools/macro_builder..." commit already on this branch left
open (that commit's README/pointer-comment half stands; it also covers
item 7).

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 22:21:27 +02:00
Niels Lohmann 73d116547a Reject ill-formed UTF-8 in CBOR/UBJSON/BJData/BSON writers, accept it in MessagePack reader
to_cbor(), to_ubjson(), to_bjdata(), and to_bson() wrote a string or object
key with ill-formed UTF-8 byte for byte, but from_cbor()/from_ubjson()/
from_bjdata()/from_bson() reject such strings with parse_error.113 since
d19f7f5dc (#5185, not yet released): a value that serialized without error
could not be read back by the same library (#5651).

CBOR (RFC 8949 Section 5), UBJSON, BJData, and BSON all require text strings
and object keys/element names to be valid UTF-8, so their writers now
validate and throw type_error.316, like to_bon8() already does. For BSON,
the check runs in the size-computation pass, before any byte is written, the
same way the binary subtype check works. check_bon8_utf8() is renamed to
check_utf8() since it is now shared by all of these writers.

MessagePack's specification explicitly allows a str object to contain an
invalid byte sequence and expects a deserializer to hand the bytes back
unchanged, so its writer is unaffected and from_msgpack() (object keys
included) no longer validates UTF-8, restoring its pre-#5185 behavior.
dump() still rejects ill-formed UTF-8 with type_error.316 unless an error
handler is passed.

Docs: add the type_error.316 exception to to_cbor/to_ubjson/to_bjdata/to_bson,
document the writer-side check on the cbor/bson/ubjson/bjdata format pages,
and rewrite the MessagePack UTF-8 warning to describe the round-trip and
dump() behavior instead of a validation requirement the spec does not have.

Tests: add ill-formed value/key cases (invalid byte, truncated sequence,
encoded surrogate, overlong encoding) expecting type_error.316 to
unit-cbor.cpp, unit-ubjson.cpp, unit-bjdata.cpp, and unit-bson.cpp (which
also checks the output vector stays empty), and turn unit-msgpack.cpp's
former parse_error.113 ill-formed-UTF-8 tests into byte-for-byte round-trip
tests for both values and keys.

This text was written by Claude Code.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 22:19:11 +02:00
Niels Lohmann 3b6ae43c53 Add JSON_DISABLE_TUPLE_REFERENCE_CONVERSION to fix std::tuple conversions (#5598)
* Add JSON_DISABLE_TUPLE_REFERENCE_CONVERSION to fix std::tuple conversions

basic_json can be constructed from std::tuple<json&>, which it turns into
a one-element array. Because of this, std::tuple picks its converting
constructor that converts the whole source tuple instead of the
element-wise one. As a result, std::tuple<const json&> built from
std::forward_as_tuple(j) binds to a temporary (a compile error with libc++,
a dangling reference with other standard libraries), and std::tuple<json>
built the same way holds [j] instead of a copy of j.

The new opt-in macro JSON_DISABLE_TUPLE_REFERENCE_CONVERSION (CMake option
JSON_DisableTupleReferenceConversion) removes the conversion from a
one-element tuple holding a reference to the same basic_json type, so
std::tuple converts element-wise. It is off by default, so existing
behavior is unchanged. It does not change any function body and therefore
is not part of the ABI tag.

Fixes #2226

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

* Convert one-element tuples to arrays on every compiler

to_json for std::tuple assigns a braced list, j = { std::get<Idx>(t)... }.
With a single element that is itself a basic_json, Apple clang 15 and 16
treat j = {x} as a copy of x, so std::tuple<json>{true} became true
instead of [true]. The macOS jobs (Xcode 15.1, 16.1) failed the new
checks in unit-disable-tuple-reference-conversion and unit-regression2.

The one-element overload that already handles
JSON_BRACE_INIT_COPY_SEMANTICS builds the array (or object, for a
[string, value] element) explicitly, the same way the initializer-list
constructor does. Use it unconditionally. The output is unchanged on
compilers that already wrapped the element.

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

* Skip json reference tuple tests on clang < 4 and GCC < 5

ci_test_compilers_gcc_old (4.8) and ci_test_compilers_clang (3.4) could
not compile the new tuple tests. Creating a std::tuple of basic_json
references, e.g. std::forward_as_tuple(j), makes these compilers
instantiate basic_json's conversion operator for libstdc++'s internal
tuple bases, which fails hard. This happens with and without
JSON_DISABLE_TUPLE_REFERENCE_CONVERSION, so it is a limitation of these
compilers, not of the new option.

Tested with the CI images: clang 3.4 to 3.9 and GCC 4.8 and 4.9 fail,
clang 4, 5, and 6 and GCC 5 and 6 compile all cases. Skip only the
checks that create such tuples; the is_constructible checks still run.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-30 20:53:56 +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 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 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 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 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 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 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 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 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 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
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 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
Niels Lohmann 918da64657 Keep BJData ndarray annotations that would not survive a round trip as objects (#5542)
write_bjdata_ndarray() encoded a JData-annotated object as a BJData
ND-array whenever its dimensions' product matched _ArrayData_.size(),
which lost information in two ways:

- _ArrayData_ was never required to be an array. null has size 0, any
  other scalar has size 1, and iterating an object visits its values, so
  e.g. {"_ArraySize_":[1],"_ArrayData_":5} was written as the array [5],
  and an object _ArrayData_ came back as an array.

- The reader only restores an annotated object from an ND-array with at
  least two non-zero dimensions that is not a 1xN row vector; an empty,
  1-D, row-vector, or zero-sized shape is read back as a plain array. The
  writer nonetheless emitted ND-array headers for these shapes, so the
  annotation was silently dropped.

OSS-Fuzz issue 563659413 hit this in parse_bjdata_fuzzer: an empty binary
_ArraySize_ is written as a plain object and read back as an empty array,
after which {"_ArrayType_":"int16","_ArraySize_":[],"_ArrayData_":null}
was encoded as the ND-array header "[$I#[]" and re-read as [], failing the
harness's value-stability check.

Such objects now fall back to a plain object encoding, which round-trips.
Genuine ND-arrays (two or more positive dimensions, not a 1xN row vector)
are encoded exactly as before. Existing fallback tests that used 1-D
shapes are moved to 2-D shapes so they keep exercising the check they
were written for, and the BJData documentation is updated.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-24 17:01:31 +02:00
Niels LohmannandClaude Sonnet 5 56b3ee566c Fix stack overflow when copying a deeply nested value (#5387) (#5389)
* Bound the descent of the copy constructor

basic_json's copy constructor copied objects and arrays by handing the
container to its own copy constructor, which copy-constructs every element
and so reaches this constructor again, once per nesting level. A value
nested deeply enough exhausted the call stack and terminated the process
with a segmentation fault - no exception, nothing the caller could catch.
Parsing such a value works, as the parser is iterative, and so does
destroying one, as #1436 made destruction iterative.

Bound how far the copy descends rather than take the call stack away from
it. The first levels are copied exactly as they were - the containers copy
their own elements, which is by far the fastest way to fill them - and only
once the copy has descended 128 levels is the value below it finished
without the call stack, through an explicit worklist. Copying can therefore
no longer exhaust the stack, however deeply a value is nested, while a value
nested less deeply than the bound - all but a vanishing minority - is copied
by the very same code as before and pays only for one counter.

That counter lives in thread_local storage, as one shared between threads
would be raced. JSON_NO_THREAD_LOCAL switches it off for toolchains without
thread_local; copying then goes through the worklist right away, which
yields the same values but is measurably slower.

The deferred values are completed before the copy they belong to returns, so
a value copied while another copy is going on - by a custom base class, say -
is unaffected by the copy it is nested in.

operator= takes its argument by value, so copy assignment is fixed as well.

Copying is as fast as it was, within measurement noise (medians of 9
interleaved runs, clang -O3): -1.3% for an array of strings, +0.0% for a
flat object, +0.1% for a flat array of numbers, +0.3% for nested arrays,
+0.6% for nested objects and +1.2% for a twitter-like document. Copying a
three-key object costs about ten nanoseconds more, the counter. Deferring
every level instead, rather than only those below the bound, measured
between 3% and 9% slower depending on the shape of the value.

This fixes #5387 for the copy constructor. dump() is still recursive.

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

* Test the copy constructor's iterative path in CI

The copy constructor descends into 128 levels before it finishes a value
without the call stack, so the iterative path is otherwise only reached
by the few tests that nest deeper than that.

JSON_NO_THREAD_LOCAL switches the descent off, which sends every value
down that path. Running the whole test suite that way covers it with
every object type, string type, allocator, and base class the suite
already exercises. The new ci_test_no_thread_local target does that; the
macro had no build coverage at all before.

Copying a nested value also has to carry over what the element-wise copy
constructor would have copied: the parents that JSON_DIAGNOSTICS relies
on, and the positions that JSON_DIAGNOSTIC_POSITIONS reports. Both are
now checked on either side of the descent bound, for objects and arrays.
Neither was tested before, and dropping either one makes the new tests
fail.

Also quantify what JSON_NO_THREAD_LOCAL costs a copy instead of calling
it "measurably slower".

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

* Split the regression tests so that they keep linking

Linking test-regression2 fails with "relocation truncated to fit:
IMAGE_REL_AMD64_REL32 against `.rdata'" once its object grows past what
the MinGW linker copes with, and the copy constructor's helpers push it
over: the object grows by 6.3%, from 4,654,128 to 4,944,920 bytes at -O0,
and develop links at the smaller of the two.

Building the tests optimized shrinks the object enough to link, but the
binaries clang 11.0.1 and clang 18.1.8 then produce crash before doctest
prints its first line - 39 of 102 tests on clang 18 - so the objects have
to become smaller rather than denser.

Moving the test cases that follow "regression tests 2" into a file of
their own brings that object to 4,687,888 bytes, which is 0.7% above the
size that links today rather than 6.3%. Both files still build for C++11,
C++17 and C++20, and run the same 9 test cases and 135 assertions as
before, now spread over two binaries.

New regression tests belong in unit-regression3.cpp from here on, which
is what CONTRIBUTING.md now says.

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

* Do not use thread_local storage with Clang targeting MinGW

Every test that copies a value segfaults there - 42 of 105 on clang
11.0.1, 39 of 102 on clang 18.1.8 - while the same tests pass with GCC
targeting MinGW, with Clang targeting MSVC, and with every other
toolchain the library is tested on. The counter that bounds the copy
constructor's descent is the library's first use of thread_local, so
that job had never exercised it before.

JSON_NO_THREAD_LOCAL already covers toolchains without thread_local
storage, and copying yields the same values with it, only more slowly.
Define it for this one automatically.

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

* Balance the warning suppression the split separated

unit-regression2.cpp opens a DOCTEST_CLANG_SUPPRESS_WARNING_PUSH block at
the top and closed it at the very bottom, which the split moved into
unit-regression3.cpp: one file was left with a push and no pop, the other
with a pop and no push, which clang reports as an error.

Give each file the pair it needs.

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

* Check both shapes without a C-style array

clang-tidy rejects the array the two shapes were iterated over
(cppcoreguidelines-avoid-c-arrays). The array only existed because astyle
reformats a range-for over a braced initializer list into something
unreadable; naming the two cases avoids both.

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

* Split the regression tests far enough to leave room

The first split left unit-regression2.cpp 0.7% below the size develop
links at, which the comparison change in the follow-up immediately used
up: the MinGW linker fails on test-regression2_cpp20 again, naming
copy_shallow and to_partial_ordering among the relocations it cannot fit.

Move the sections from "issue #2067" on, and the helper types they use,
so that the file stops being the one that decides whether the tests can
be linked at all. At -O0 and C++20, unit-regression2.cpp is now 2,964,944
bytes against develop's 4,708,248, and 3,070,568 bytes with the follow-up
applied - roughly a third smaller either way, rather than a fraction of a
percent larger.

The 135 assertions are the same ones as before, now spread over three
test cases in two files.

Also silence the clang-tidy findings the deep-nesting tests draw: the
copies they make are what is being tested, and the reserve() computation
gets its parentheses.

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

* Move the #4804 alias to the file that uses it

The split left the json_4804 alias behind in unit-regression2.cpp while
the test case that uses it went to unit-regression3.cpp, which does not
build for C++17 and C++20 as a result.

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

* Include <span> where the split moved its only use

The #2546 test case guards itself with __has_include(<span>), but the
include itself sat in unit-regression2.cpp's preamble and stayed behind,
so the section compiled without a declaration wherever the guard passed -
which nvhpc reported and libc++ builds do not, as they skip the section
altogether.

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

* Keep the descent bookkeeping in one place

Copying carried a depth count, a depth limit and a guard of its own, and
the comparison in the follow-up added a second set beside them. Neither
operation needs its own: they are never nested inside one another by the
library - copying a value does not compare one, and comparing two values
does not copy them - and where user code nests them anyway, sharing the
count only ends a descent sooner than it had to.

So there is now one nesting_depth(), one nesting_depth_limit() and one
nesting_depth_guard, which the follow-up uses instead of adding its own.
Inverting the test in copy_structured leaves the too-deep case and the
no-thread-local case as the same code.

The guard takes the count rather than looking it up, because the caller
has looked it up already to test it against the limit, and reaching
thread-local storage twice on the path that is taken almost every time is
worth avoiding.

The switch that copies the value of anything that is not an object or an
array was written twice - once in the copy constructor, once in
copy_shallow - so that adding a value_t meant editing both, and missing
one would have been silent. It is copy_leaf_value now, and inlined: both
callers have already sorted the containers out, and folding that test into
the switch is what keeps a value made mostly of numbers copying as fast as
it did.

Copying canada.json, citm_catalog.json and twitter.json is within 0.6% of
what it was before, measured as a paired ratio over 18 interleaved rounds
against a run-to-run spread of 0.3%.

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

* Check that an abandoned copy can still be destroyed

Copying a value without the call stack builds the copy from the top down,
and every value whose own copy has not been made yet stays a null value
until it is. That is what lets a copy be abandoned half-built: the
destructor finds nothing but complete values and null ones.

Nothing tested it. Failing an allocation part-way through a copy of a
deeply nested value does, with the allocator the file already has for
exactly this kind of test.

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

* Name the test's locals so Flawfinder stops matching them

The code scanning job reports CWE-362 - "check when opening files" - for
a test that opens no files: Flawfinder matched a local variable called
open. Rename it and its partner.

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

* Keep the descent guard's bookkeeping self-contained

nesting_depth_limit() and nesting_depth_guard were only used inside
the JSON_NO_THREAD_LOCAL-guarded branch of copy_structured(), but were
defined unconditionally. Move them inside the #ifndef, and have the
guard look up the depth and test it against the limit itself (via
okay()) instead of making the caller do it - the caller no longer
needs to touch nesting_depth() at all. Also shrink the thread-local
counter to std::uint8_t, matching what its own doc comment already
argued.

Addresses gregmarr's review comments on #5389.

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

* Make nesting_depth_guard usable regardless of JSON_NO_THREAD_LOCAL

nesting_depth_limit() and nesting_depth() stay behind #ifndef
JSON_NO_THREAD_LOCAL, since a descent cannot be bounded without a
per-thread count. But the guard itself now always exists, becoming a
no-op that is never okay() under that macro - the same way the bound
is already reached on every call without one. copy_structured() no
longer needs to know which case it is in.

This is what lets #5390 reuse the guard for comparison, which cannot
test JSON_NO_THREAD_LOCAL where the macro-based operators use it: the
guard now carries that distinction itself instead of requiring every
caller to.

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

* Silence VS2015's C4503 for the custom-base-class test

The deep-copy support added for #5387 lengthened the mangled name of
std::allocator_traits<...>::construct for the test's map type past
VS2015's limit, which /WX turns into a build failure even though the
name is only used for (now-truncated) debug info.

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

* Remove dead unused-parameter casts from copy_metadata()

@gregmarr asked whether the static_cast<void> pair in the
JSON_DIAGNOSTIC_POSITIONS-off branch was needed for an empty
json_base_class_t. It isn't: src and dst are already referenced
unconditionally by the base-class copy above, so no -Wunused-parameter
warning fires either way (checked with -Wall -Wextra
-Wunused-parameter, JSON_DIAGNOSTIC_POSITIONS 0 and 1).

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

* Fix CI: build custom array types without a fill constructor, re-amalgamate

copy_array_level() built the destination array with the fill
constructor array_t(count, value), which is not part of the array
container interface the library otherwise assumes (e.g. custom
ArrayTypes that only provide a default and an iterator-pair
constructor, as covered by unit-custom-array-type.cpp). Default-
construct the array and resize() it instead, matching how the rest
of the codebase already grows array_t.

Also re-run the amalgamation, which had fallen out of sync with
include/nlohmann/json.hpp.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
2026-09-24 17:01:15 +02:00
Niels LohmannandClaude Sonnet 5 ed513715a8 Document that a NUL byte in the input is treated as end of input (#5534)
* docs: document that a NUL byte in the input is treated as end of input

A NUL byte anywhere in the input - trailing, or embedded ahead of more
otherwise well-formed JSON - is currently treated the same as genuine
end of input, so parsing silently stops there instead of raising the
parse_error.101 any other unexpected byte triggers. This mirrors the
NUL-terminated-C-string convention already used when no explicit input
length is given (json::parse(const char*) already stops at strlen()),
just applied uniformly rather than only when a length is genuinely
unavailable.

This behavior predates this change and is not being altered here -
changing it would be an observable, backwards-incompatible behavior
change for any caller that (knowingly or not) depends on it, which is
not something to do silently in a patch. Documenting the current,
verified behavior as a new FAQ entry instead, so it's an intentional
and discoverable part of the contract rather than a surprise.

Fixes #5530.

Signed-off-by: Niels Lohmann <niels.lohmann@gmail.com>
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N4RQ1Ahan5YAGbnAQGjZTY

* Add JSON_STRICT_NUL_HANDLING opt-in macro for issue #5530

A NUL byte anywhere in the input is currently treated the same as real
end of input, rather than raising parse_error.101 like any other
unexpected byte (documented in the previous commit's FAQ entry). A full
unconditional fix was tried in PR #5532 but rejected as too risky to
ship by default: any caller could depend on the current behavior, even
unknowingly (e.g. a zero-padded buffer). On PR #5534, gregmarr proposed
a compile-time opt-in flag instead, and the maintainer agreed, wanting
it available now and defaulting to the corrected behavior in 4.0.0.

This mirrors the existing JSON_BRACE_INIT_COPY_SEMANTICS precedent as
closely as sensible:
- JSON_STRICT_NUL_HANDLING defaults to 0 (off); the three lexer sites
  that treat '\0' as EOF/comment-terminator are gated with
  `#if !JSON_STRICT_NUL_HANDLING` so the default-off behavior is
  byte-for-byte identical to today's.
- input_adapters.hpp's `T (&array)[N]` overload additionally trims a
  single trailing '\0' from a `char` array (e.g. a string literal like
  `json::parse("123")`) when the macro is on, so that case keeps
  working; every other element type (unsigned char, std::uint8_t, ...)
  always keeps its full extent. This intentionally does *not* reuse the
  existing strlen()-based pointer overload via SFINAE-excluding `char`
  from the array overload, as originally sketched for this change: that
  approach is ambiguous against the newer generic container overload
  added since PR #5532, and even where it compiles, strlen()-scanning a
  `char` array that is not NUL-terminated within its bounds reads past
  the end of the array (confirmed with AddressSanitizer). Trimming only
  a single trailing byte, without scanning, avoids both problems.
- Documented via docs/mkdocs/docs/api/macros/json_strict_nul_handling.md,
  linked from the macros index/nav/features page, the FAQ entry, and
  the parse/accept/operator>> reference pages.
- Tested in unit-class_parser.cpp and unit-deserialization.cpp, default
  state unguarded and opt-in state guarded. Since the library itself
  #undefs the macro at the end of json.hpp (as JSON_BRACE_INIT_COPY_SEMANTICS
  already does), a plain `#if defined(JSON_STRICT_NUL_HANDLING)` guard
  after the include never actually triggers; the tests instead capture
  the command-line value into a test-local macro before including the
  header. A few pre-existing fixtures elsewhere (std::array<uint8_t, N>
  sized one larger than their literal, relying on value-initialization
  to silently add a trailing zero byte) needed the same one-byte
  adjustment to keep passing under the opt-in behavior.

Unlike the precedent, this adds a proper `JSON_StrictNulHandling` CMake
option (rather than a raw -DCMAKE_CXX_FLAGS injection) and wires its
ci_test_strict_nul_handling target into the ci_cmake_options job matrix
in .github/workflows/ubuntu.yml, so the opt-in build is actually
exercised in CI -- closing the one gap in the precedent's own CI setup
(ci_test_brace_init_copy_semantics is defined but never referenced by
any workflow, so it has never actually run).

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

* Clarify where JSON_STRICT_NUL_HANDLING does not reject NUL bytes

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

---------

Signed-off-by: Niels Lohmann <niels.lohmann@gmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
2026-09-24 06:55:21 +02:00
Niels LohmannandClaude 1054b2097e Speed up binary writing: value-type output sink + byte-swap number encoding (#5286)
* Devirtualize binary_writer via a value-type output sink

to_cbor/to_msgpack/to_ubjson/to_bjdata/to_bson wrote every byte through
output_adapter_t, a shared_ptr<output_adapter_protocol> whose
write_character/write_characters are virtual. Unlike the lexer (templated
on a concrete InputAdapterType), the binary writer never got that
treatment, so binary output paid a vtable lookup per byte and a
make_shared per call.

Template binary_writer on an OutputSinkType and give it two concrete,
non-virtual sinks:

- output_vector_sink: appends straight into a std::vector (push_back /
  insert), used by the vector-returning to_* convenience functions. No
  vtable, no shared_ptr; the writes inline.
- output_adapter_sink: forwards to a type-erased output_adapter_t, so the
  existing to_*(j, output_adapter) overloads (streams, strings, custom
  adapters) keep working exactly as before -- one virtual call each,
  unchanged.

binary_writer keeps a convenience constructor taking output_adapter_t
(building the default output_adapter_sink), so the adapter overloads are
untouched; only the convenience functions switch to the vector sink. The
friend declaration and the basic_json binary_writer alias gain the new
(defaulted) template parameter.

Output is byte-for-byte identical: verified across ~3000 randomized
values plus curated edge cases (all scalar widths, strings with invalid
UTF-8, binary, nested arrays/objects) for CBOR, MessagePack, UBJSON (both
size/type settings), BJData, and BSON, plus the output_adapter path, in
C++11/17/20. Warning-clean under clang -Weverything and the gcc pedantic
set; clang-tidy clean on the changed headers; make check-amalgamation
clean.

Throughput (g++ -O3, vs develop): scalar-dense binary output such as
integer arrays ~1.4x; many small to_cbor calls ~1.04x (DOM traversal
bound); string/blob-heavy output unchanged (already bulk-bound). No
workload regressed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix CI failures from binary_writer output-sink change

Four CI jobs failed on the initial commit; all are addressed here without
changing any output (binary encodings remain byte-for-byte identical to
develop across the differential corpus):

1. ci_test_gcc / cuda (-Werror=duplicated-branches): for number_float_t ==
   float, static_cast<float>(n) is the identity, so write_compact_float's
   two branches are intentionally identical. Once the concrete vector sink
   is inlined, GCC constant-folds and diagnoses this (the type-erased path
   hid it behind a non-inlined virtual call). Silence -Wduplicated-branches
   for GCC (clang has no such warning) alongside the existing -Wfloat-equal
   pragma.

2. ci_static_analysis_clang (UBSan nonnull-attribute): binary_writer passes
   a null pointer with length 0 for empty strings/binary. output_vector_sink
   / output_adapter_sink declared write_characters JSON_HEDLEY_NON_NULL, so
   the sanitizer flagged the (harmless) zero-length call once the sink was
   called directly rather than through the attribute-free virtual base. Drop
   the attribute from both sinks, matching the pre-existing behavior.

3. ci_cpplint (build/include_what_you_use): output_adapter_sink uses
   std::move; add #include <utility>.

4. ci_cuda_example (nvcc 11.8): NVCC's front end rejects the default
   template argument on the binary_writer alias template. Revert the alias
   to its original single-parameter form (relying on binary_writer's own
   defaulted OutputSinkType) and spell out the full type in the vector-sink
   convenience functions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Encode big-endian numbers with a byte swap instead of std::reverse

write_number() reordered multi-byte numbers for the big-endian formats
(CBOR/MessagePack/UBJSON) with std::reverse over the byte array. GCC
lowered only some sizes to a bswap; clang kept a scalar byte shuffle
(0 bswap instructions in the CBOR number path). Replace the reverse with
size-dispatched __builtin_bswap16/32/64 helpers (portable shift fallback
for other compilers; std::reverse retained for exotic sizes such as a
long double number_float_t).

Codegen: the CBOR number path now emits bswap on both compilers
(gcc 2 -> 16, clang 0 -> 4). Output is byte-for-byte identical to the
previous implementation across the binary differential corpus.

Throughput (isolated vs the std::reverse version, best of 9):
  CBOR int64 array   gcc +7%   clang +10%
  CBOR uint16 array  gcc +27%  clang flat

Modest but consistent on number-dense encodings; negligible on
string/blob-heavy output, as expected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Reserve output capacity up front for binary serialization

The vector-returning to_cbor/to_msgpack/to_ubjson/to_bjdata/to_bson grew
the output buffer purely by geometric reallocation. Reserving an estimate
up front avoids the early reallocations, which is the dominant per-byte
cost for array/object-heavy output.

The estimate (binary_reserve_hint) is deliberately conservative and safe
against untrusted input: it consults only the top-level element count
(O(1), no walk of the DOM), guards the multiplication against overflow,
and clamps the result to a fixed 1 MiB ceiling, so a large or hostile DOM
can never force an oversized allocation here. The buffer still grows
geometrically past the hint, so an underestimate only costs a few later
reallocations; scalars/strings/binary are written in one shot and get no
hint. Reserving capacity does not change the bytes produced.

Throughput (g++/clang -O3, vs the previous commit):
  cbor int array     +10% / +13%
  cbor object array  +20% / +38%

Output is byte-for-byte identical to develop across the binary
differential corpus.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Address review findings on the binary writer output sinks

- binary_reserve_hint(): the 4-bytes-per-element estimate over-reserved by up
  to 4x for arrays of small scalars (CBOR encodes 0..23 in one byte), and the
  returned vector kept that capacity. Make the hint a strict lower bound on the
  encoded size instead, which also removes the 1 MiB clamp whose branch no test
  could reach (the largest container in the suite has 65793 elements).

- Guard the -Wduplicated-branches pragma with __GNUC__ >= 7. The warning does
  not exist before GCC 7, so naming it made GCC 4.8/4.9/5/6 - which the CI
  matrix still builds - warn under -Wpragmas on every including translation
  unit, breaking downstream -Werror builds.

- Constrain the adapter constructor of binary_writer with the enable_if its
  documentation already claimed, so a writer over some other sink type is no
  longer advertised as constructible from an output adapter.

- Let output_vector_adapter wrap output_vector_sink rather than duplicating the
  append logic, so the type-erased and templated paths share one implementation.

- Collapse the three copies of the memcpy/byte_swap/memcpy dance into a single
  byte_swap_buffer() helper, and add the MSVC _byteswap_* intrinsics so MSVC no
  longer falls back to the scalar shuffle this change exists to eliminate.

- Add a vector_writer() helper for the five vector-returning to_* overloads
  instead of spelling out the writer type at each call site, and drop a dead
  default member initializer on output_adapter_sink.

- New tests: the vector sink and the adapter sink must produce identical bytes
  for every format (the two to_* overloads no longer delegate to each other and
  could otherwise drift), and binary_reserve_hint() must never exceed the size
  actually written.

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

* Route the -Wduplicated-branches pragma through Hedley

Match #5485, which moved the binary writer's hand-rolled diagnostic
pragmas onto JSON_HEDLEY_PRAGMA (merged into develop while this branch
was open). The devirtualization's -Wduplicated-branches suppression in
write_compact_float was the one raw '#pragma GCC diagnostic' left; it
now uses JSON_HEDLEY_PRAGMA like the adjacent -Wfloat-equal line, still
guarded to GCC >= 7 and non-clang (the warning exists only there).

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
2026-09-23 08:59:46 +02:00
Niels Lohmann 0b20b7e622 Reject MessagePack/BSON binary subtypes that don't fit their wire format (#5469)
* Reject MessagePack/BSON binary subtypes that don't fit their wire format

Both formats store byte_container_with_subtype's subtype (a uint64_t)
in a single byte. The writers cast to std::int8_t/std::uint8_t without
a range check, so subtypes above 255 were silently truncated modulo
256 instead of raising an error. Throw out_of_range.413 instead when
the subtype exceeds the representable range of 0-255.

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

* Move the new binary-subtype regression test out of unit-regression2.cpp

unit-regression2.cpp is already at the edge of what the MinGW linker
can relocate; adding this test's ~26 lines tips test-regression2_cpp20
(clang, Windows) over into "relocation truncated to fit:
IMAGE_REL_AMD64_REL32 against `.rdata'" (see 8ce64b9c1 / b82717c8a for
the same failure mode). Split the test along format lines instead:
MessagePack assertions move to unit-msgpack.cpp, BSON assertions to
unit-bson.cpp. The CBOR round-trip guard is dropped as redundant --
unit-cbor.cpp's "Tagged values" section already round-trips subtypes
up to 8589934590, far past the 70000 checked here.

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-22 21:52:32 +02:00
Niels Lohmann a2b19d6158 Honor allow_exceptions=false for excessive array/object size (out_of_range.408) (#5467)
* Honor allow_exceptions=false for excessive array/object size (out_of_range.408)

The SAX DOM parsers' start_object()/start_array() threw out_of_range.408
directly via JSON_THROW when a binary format (CBOR/UBJSON/BJData) declared
a container size exceeding max_size(), bypassing the allow_exceptions flag
that every other malformed-input error path in these classes honors via
parse_error(). This meant that json::from_cbor(data, true, false) etc.
could still throw (or abort under JSON_NOEXCEPTION) instead of returning a
discarded value, contrary to the allow_exceptions=false contract.

Route all four call sites (two in json_sax_dom_parser, two in
json_sax_dom_callback_parser) through parse_error() instead, matching the
existing error-handling pattern used elsewhere in this file. Behavior is
unchanged when allow_exceptions is true (the default); the exception
message and type are identical.

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

* Drop a non-portable exact exception message check in the 408 test

The allow_exceptions=false regression test checked the exact message
text produced when allow_exceptions=true (the default). On platforms
where std::size_t is 32-bit (e.g. mingw x86, MSVC Win32 builds), a
declared CBOR length of 2^63 is intercepted earlier, by
get_cbor_container_size()'s own (pre-existing, already correct)
length-narrowing check, with different wording than this fix's
start_array()/start_object() size check -- same error code, same
"still throws when allow_exceptions=true" guarantee, different text.

CHECK_THROWS_AS already verifies the behavior this test cares about
(still throws json::out_of_range, unchanged); drop the exact-message
assertion since it isn't portable across size_t widths and doesn't
add coverage of this fix specifically.

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

* Fix -Werror=unused-result on json::from_cbor() in the 408 regression test

from_cbor() is [[nodiscard]]; CHECK_THROWS_AS() otherwise discards its
result, which GCC flags under -Werror. Assign to a throwaway json, as
the rest of the suite already does for from_cbor()/from_msgpack().

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-09-22 21:52:31 +02:00