Avoid deep recursion in serialization write-buffer test

The "many small structural writes exceed the write buffer" subcase built
a 1100-deep nested array and dumped it to force >1024 consecutive
single-character writes through put_char (exercising the write buffer's
flush-when-full branch). dump() recurses per nesting level, so on MSVC
debug builds (smaller default stack, larger frames) this overflowed the
stack and crashed test-serialization; Linux/macOS have enough headroom to
hide it.

Replace the nesting with a flat array of 500 empty strings. Each element
emits '"', '"', ',' via put_char, so the dump is a long run of
single-character writes (1501 bytes > the 1024-byte buffer) at nesting
depth two, hitting the same flush branch without deep recursion. Library
code is unchanged.

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>

.github/workflows/codeql-analysis.yml

@@ -38,14 +38,14 @@ jobs:
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+      uses: github/codeql-action/init@e4fba868fa4b1b91e1fdab776edc8cfbe6e9fb81 # v4.37.3
       with:
         languages: c-cpp
 
     # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
     # If this step fails, then you should remove it and run the build manually (see below)
     - name: Autobuild
-      uses: github/codeql-action/autobuild@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+      uses: github/codeql-action/autobuild@e4fba868fa4b1b91e1fdab776edc8cfbe6e9fb81 # v4.37.3
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+      uses: github/codeql-action/analyze@e4fba868fa4b1b91e1fdab776edc8cfbe6e9fb81 # v4.37.3

.github/workflows/flawfinder.yml

@@ -43,6 +43,6 @@ jobs:
           output: 'flawfinder_results.sarif'
 
       - name: Upload analysis results to GitHub Security tab
-        uses: github/codeql-action/upload-sarif@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+        uses: github/codeql-action/upload-sarif@e4fba868fa4b1b91e1fdab776edc8cfbe6e9fb81 # v4.37.3
         with:
           sarif_file: ${{github.workspace}}/flawfinder_results.sarif

.github/workflows/scorecards.yml

@@ -46,7 +46,7 @@ jobs:
           persist-credentials: false
 
       - name: "Run analysis"
-        uses: ossf/scorecard-action@4eaacf0543bb3f2c246792bd56e8cdeffafb205a # v2.4.3
+        uses: ossf/scorecard-action@2d1146689b8cda280b9bc96326124645441f03bc # v2.4.4
         with:
           results_file: results.sarif
           results_format: sarif
@@ -76,6 +76,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+        uses: github/codeql-action/upload-sarif@e4fba868fa4b1b91e1fdab776edc8cfbe6e9fb81 # v4.37.3
         with:
           sarif_file: results.sarif

.github/workflows/semgrep.yml

@@ -61,7 +61,7 @@ jobs:
 
       # Upload SARIF file generated in previous step
       - name: Upload SARIF file
-        uses: github/codeql-action/upload-sarif@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+        uses: github/codeql-action/upload-sarif@e4fba868fa4b1b91e1fdab776edc8cfbe6e9fb81 # v4.37.3
         with:
           sarif_file: semgrep.sarif
         if: always()

.github/workflows/stale.yml

@@ -20,7 +20,7 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: actions/stale@1e223db275d687790206a7acac4d1a11bd6fe629 # v10.4.0
+      - uses: actions/stale@4391f3da665fdf50b6810c1a66712fb9ba21aa93 # v11.0.0
         with:
           stale-issue-label: 'state: stale'
           stale-pr-label: 'state: stale'

.github/workflows/ubuntu.yml

@@ -142,7 +142,7 @@ jobs:
           name: code-coverage-report
           path: ${{ github.workspace }}/build/html
       - name: Publish report to Coveralls
-        uses: coverallsapp/github-action@5cbfd81b66ca5d10c19b062c04de0199c215fb6e # v2.3.7
+        uses: coverallsapp/github-action@8d6379e14d29928660c4ba802d8e85393440b329 # v2.3.8
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           path-to-lcov: ${{ github.workspace }}/build/json.info.filtered.noexcept

README.md

@@ -1801,13 +1801,13 @@ The library itself consists of a single header file licensed under the MIT licen
 - [**amalgamate.py - Amalgamate C source and header files**](https://github.com/edlund/amalgamate) to create a single header file
 - [**American fuzzy lop**](https://lcamtuf.coredump.cx/afl/) for fuzz testing
 - [**AppVeyor**](https://www.appveyor.com) for [continuous integration](https://ci.appveyor.com/project/nlohmann/json) on Windows
-- [**Artistic Style**](http://astyle.sourceforge.net) for automatic source code indentation
+- [**Artistic Style**](https://astyle.sourceforge.net) for automatic source code indentation
 - [**Clang**](https://clang.llvm.org) for compilation with code sanitizers
 - [**CMake**](https://cmake.org) for build automation
 - [**Codacy**](https://www.codacy.com) for further [code analysis](https://app.codacy.com/gh/nlohmann/json/dashboard)
 - [**Coveralls**](https://coveralls.io) to measure [code coverage](https://coveralls.io/github/nlohmann/json)
 - [**Coverity Scan**](https://scan.coverity.com) for [static analysis](https://scan.coverity.com/projects/nlohmann-json)
-- [**cppcheck**](http://cppcheck.sourceforge.net) for static analysis
+- [**cppcheck**](https://cppcheck.sourceforge.io) for static analysis
 - [**doctest**](https://github.com/onqtam/doctest) for the unit tests
 - [**GitHub Changelog Generator**](https://github.com/skywinder/github-changelog-generator) to generate the [ChangeLog](https://github.com/nlohmann/json/blob/develop/ChangeLog.md)
 - [**Google Benchmark**](https://github.com/google/benchmark) to implement the benchmarks
@@ -1822,6 +1822,15 @@ The library itself consists of a single header file licensed under the MIT licen
 
 ## Notes
 
+### Standards compliance
+
+The library targets strict conformance with [RFC 8259](https://tools.ietf.org/html/rfc8259.html). Both the original [JSONTestSuite](https://github.com/nst/JSONTestSuite) and its updated revision are exercised in CI; their test data is downloaded from [`nlohmann/json_test_data`](https://github.com/nlohmann/json_test_data) at configure time rather than committed to this repository (see [`tests/src/unit-testsuites.cpp`](https://github.com/nlohmann/json/blob/develop/tests/src/unit-testsuites.cpp)):
+
+- The updated revision runs all mandatory `y_` (must-accept) and `n_` (must-reject) cases through the strict [`parse()`](https://json.nlohmann.me/api/basic_json/parse/) entry point; the original suite runs its `n_` cases through `parse()` and its `y_` cases through [`operator>>`](https://json.nlohmann.me/api/operator_gtgt/).
+- The `i_` (implementation-defined) cases are, by RFC 8259, free to be accepted *or* rejected, so "passing all `i_` cases" is not a meaningful conformance metric. The library makes deliberate, documented choices there: nesting depth is not artificially limited, a leading UTF-8 byte order mark is silently ignored, [Unicode noncharacters](https://www.unicode.org/faq/private_use.html#nonchar1) are forwarded unchanged, invalid UTF-8 and lone/unpaired UTF-16 surrogates are rejected (stricter than required), and a number that cannot be stored without becoming `NaN`/`INF` raises [`out_of_range.406`](https://json.nlohmann.me/home/exceptions/#jsonexceptionout_of_range406).
+
+One behavioral nuance is worth calling out, because a superficial test often misreads it as non-compliance: [`parse()`](https://json.nlohmann.me/api/basic_json/parse/) is strict and rejects trailing data after a value, whereas [`operator>>`](https://json.nlohmann.me/api/operator_gtgt/) follows relaxed iostream semantics — it parses a single value and leaves the stream positioned right after it. Feeding "a valid document followed by trailing bytes" through `operator>>` reports success; the same input through `parse()` is rejected. This is a documented two-API design, not a conformance gap. See [**parsing**](https://json.nlohmann.me/features/parsing/) for details.
+
 ### Character encoding
 
 The library supports **Unicode input** as follows:

cmake/clang_flags.cmake

@@ -5,6 +5,9 @@
 # -Wno-extra-semi-stmt            The library uses assert which triggers this warning.
 # -Wno-padded                     We do not care about padding warnings.
 # -Wno-covered-switch-default     All switches list all cases and a default case.
+# -Wno-c2y-extensions             Clang 22.1 diagnoses __COUNTER__ as a C2y extension, also in
+#                                 C++ mode. The library does not use __COUNTER__; the warnings
+#                                 all come from vendored Doctest (SECTION/TEST_CASE macros).
 # -Wno-unsafe-buffer-usage        Pervasive: the library's own low-level numeric/buffer code
 #                                 (to_chars, serializer, lexer, binary reader/writer, input
 #                                 adapters, json_pointer) plus vendored Doctest itself (~208
@@ -20,5 +23,6 @@ set(CLANG_CXXFLAGS
     -Wno-extra-semi-stmt
     -Wno-padded
     -Wno-covered-switch-default
+    -Wno-c2y-extensions
     -Wno-unsafe-buffer-usage
 )

docs/mkdocs/docs/api/basic_json/binary_t.md

@@ -13,9 +13,8 @@ is compatible with both of the binary data formats that use binary subtyping, (t
 incompatible with each other, and it is up to the user to translate between them). The subtype is added to `BinaryType`
 via the helper type [byte_container_with_subtype](../byte_container_with_subtype/index.md).
 
-[CBOR's RFC 7049](https://tools.ietf.org/html/rfc7049) describes this type as:
-> Major type 2: a byte string. The string's length in bytes is represented following the rules for positive integers
-> (major type 0).
+[CBOR's RFC 8949](https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1) describes this type as:
+> Major type 2: A byte string. The number of bytes in the string is equal to the argument.
 
 [MessagePack's documentation on the bin type
 family](https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family) describes this type as:

docs/mkdocs/docs/api/basic_json/parser_callback_t.md

@@ -29,7 +29,14 @@ Discarding a value (i.e., returning `#!cpp false`) has different effects dependi
 called:
 
 - Discarded values in structured types are skipped. That is, the parser will behave as if the discarded value was never
-  read.
+  read. This holds for every value type and for both kinds of parent: a discarded element is removed from the
+  surrounding array, and a discarded member is removed from the surrounding object together with its key.
+- Arrays and objects can be discarded either at their `parse_event_t::array_start`/`parse_event_t::object_start` event
+  or at their `parse_event_t::array_end`/`parse_event_t::object_end` event, and both remove the whole value. Discarding
+  it at the start event also means the callback is called neither for the content of the value nor for its matching end
+  event.
+- Discarding a `parse_event_t::key` event discards the whole object member. The callback is still called for the
+  associated value, but its return value has no further effect.
 - In case a value outside a structured type is skipped, it is replaced with `null`. This case happens if the top-level
   element is skipped.
 
@@ -49,7 +56,7 @@ called:
 ## Return value
 
 Whether the JSON value which called the function during parsing should be kept (`#!cpp true`) or not (`#!cpp false`). In
-the latter case, it is either skipped completely or replaced by an empty discarded object.
+the latter case, it is skipped completely, or replaced by `null` if it is the top-level value.
 
 ## Examples
 
@@ -68,6 +75,21 @@ the latter case, it is either skipped completely or replaced by an empty discard
     --8<-- "examples/parse__string__parser_callback_t.output"
     ```
 
+??? example
+
+    The example below shows where discarded values are removed. The array and the number are discarded in different
+    ways, but in each case the parse result contains neither the value nor its key.
+
+    ```cpp
+    --8<-- "examples/parser_callback_t.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/parser_callback_t.output"
+    ```
+
 ## See also
 
 - [parse](parse.md) deserialize from a compatible input
@@ -76,3 +98,5 @@ the latter case, it is either skipped completely or replaced by an empty discard
 ## Version history
 
 - Added in version 1.0.0.
+- Fixed in version 3.13.0 to also remove discarded values from a parent object; before, discarding an array or a value
+  stored under an object key left a discarded member behind, which made the parse result serialize to invalid JSON.

docs/mkdocs/docs/api/macros/index.md

@@ -24,6 +24,7 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**JSON_NO_IO**](json_no_io.md) - switch off functions relying on certain C++ I/O headers
 - [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](json_skip_unsupported_compiler_check.md) - do not warn about unsupported compilers
 - [**JSON_USE_GLOBAL_UDLS**](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
+- [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
 
 ## Library version
 

docs/mkdocs/docs/api/macros/json_use_simdutf.md

@@ -0,0 +1,52 @@
+# JSON_USE_SIMDUTF
+
+```cpp
+#define JSON_USE_SIMDUTF
+```
+
+When defined, the parser validates the UTF-8 content of JSON strings that come from a **contiguous byte input**
+(`std::string`, `std::vector<char>`/`<std::uint8_t>`, string literals, `const char*` ranges, …) using the
+[simdutf](https://github.com/simdutf/simdutf) library instead of the built-in scalar validator. On text with many
+non-ASCII characters (e.g. CJK or emoji) this can validate several times faster.
+
+This is an **opt-in external dependency**. The library itself remains header-only and its behavior is unchanged: the
+same input is accepted or rejected either way, and every parse error is reported at the same position with the same
+message (simdutf is only used to fast-path *valid* runs; anything it flags falls back to the scalar path so the exact
+diagnostic is preserved). Streaming inputs (files, `std::istream`, wide strings, user-defined adapters) always use the
+scalar path.
+
+When `JSON_USE_SIMDUTF` is defined you must make the `simdutf.h` header available on the include path and link the
+simdutf library. When it is not defined, no simdutf header is included and there is no dependency.
+
+## Default definition
+
+By default, `#!cpp JSON_USE_SIMDUTF` is not defined and the portable C++11 scalar validator is used.
+
+```cpp
+#undef JSON_USE_SIMDUTF
+```
+
+## Examples
+
+??? example
+
+    The code below enables the simdutf backend for UTF-8 validation.
+
+    ```cpp
+    #define JSON_USE_SIMDUTF 1
+    #include <simdutf.h>
+    #include <nlohmann/json.hpp>
+
+    ...
+    ```
+
+    The project must also link against simdutf, e.g. with CMake:
+
+    ```cmake
+    target_compile_definitions(your_target PRIVATE JSON_USE_SIMDUTF)
+    target_link_libraries(your_target PRIVATE simdutf::simdutf)
+    ```
+
+## Version history
+
+- Added in version 3.12.1.

docs/mkdocs/docs/api/operator_gtgt.md

@@ -33,17 +33,44 @@ A UTF-8 byte order mark is silently ignored.
 Invalid Unicode escapes and unpaired surrogates in the input are reported as
 [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) with a detailed message.
 
-`operator>>` parses exactly one JSON value and leaves the stream positioned right after it, so it can be called
-repeatedly to read a sequence of concatenated JSON values from the same stream:
+`operator>>` parses exactly one JSON value, so it can be called repeatedly to read a sequence of concatenated JSON
+values from the same stream:
 
 ```cpp
 json j1, j2;
-input >> j1;  // parses the first value, stream now positioned right after it
+input >> j1;  // parses the first value
 input >> j2;  // parses the next value
 ```
 
-Note this does **not** work for [JSON Lines](../features/parsing/json_lines.md) (newline-delimited JSON) input --
-see that page for why and for the recommended alternative.
+!!! warning "A number must be followed by whitespace"
+
+    A number is only terminated by the character that follows it. That character is read from the stream to detect the
+    end of the number, and it is **not** put back. When a value that is a number is immediately followed by the next
+    value, the first character of that next value is lost:
+
+    ```cpp
+    std::istringstream input("1true");
+    json j1, j2;
+    input >> j1;  // j1 == 1
+    input >> j2;  // throws parse_error.101: the stream now starts at "rue"
+    ```
+
+    Separating the values with whitespace avoids this, because the character that is eaten is then the separator:
+
+    ```cpp
+    std::istringstream input("1 true");
+    json j1, j2;
+    input >> j1;  // j1 == 1
+    input >> j2;  // j2 == true
+    ```
+
+    Only numbers are affected. Values ending in a self-delimiting character do not read past themselves, so
+    `truefalse`, `[1][2]`, `{"a":1}{"b":2}`, and `"a""b"` can be read back to back without a separator.
+
+    This is tracked in [#5340](https://github.com/nlohmann/json/issues/5340).
+
+Note that reading concatenated values does **not** work for [JSON Lines](../features/parsing/json_lines.md)
+(newline-delimited JSON) input -- see that page for why and for the recommended alternative.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/ordered_json.md

@@ -13,6 +13,12 @@ Therefore, adding object elements can yield a reallocation in which case all ite
 [`end()`](basic_json/end.md) iterator) and all references to the elements are invalidated. Also, any iterator or
 reference after the insertion point will point to the same index, which is now a different value.
 
+## Complexity
+
+[`ordered_map`](ordered_map.md) has no lookup index: every key-based object operation is a linear scan, so building or
+parsing an object of `n` keys costs O(n²) rather than O(n log n). See
+[`ordered_map` complexity](ordered_map.md#complexity) for the per-operation table and for measured numbers.
+
 ## Examples
 
 ??? example

docs/mkdocs/docs/api/ordered_map.md

@@ -56,6 +56,48 @@ std::equal_to<>     // since C++14
 - **find**
 - **insert**
 
+## Complexity
+
+Because the elements are stored in a `std::vector` in insertion order, there is no index to look a key up by. Every
+key-based operation performs a **linear scan** over the stored elements. With `n` denoting the number of elements in the
+container:
+
+| Operation                              | Complexity     | Note                                                     |
+|----------------------------------------|----------------|----------------------------------------------------------|
+| **emplace**                            | O(n)           | scans for an existing key, then appends (amortized O(1)) |
+| **operator\[\]**                       | O(n)           | delegates to **emplace** (non-const) or **at** (const)   |
+| **at**                                 | O(n)           | throws `#!cpp std::out_of_range` if the key is not found |
+| **find**                               | O(n)           |                                                          |
+| **count**                              | O(n)           | the result is always 0 or 1                              |
+| **erase(key)**                         | O(n)           | scan, then move the remaining elements one position down |
+| **erase(pos)**, **erase(first, last)** | O(n)           | moves all elements after the erased range                |
+| **insert(value)**                      | O(n)           | equivalent to **emplace**                                |
+| **insert(first, last)**                | O((n + m) * m) | for `m` inserted elements                                |
+
+This differs from `#!cpp std::map`, where the same operations are O(log n).
+
+!!! warning "Quadratic cost of building large objects"
+
+    Because every insertion scans all elements inserted so far, building an object of `n` distinct keys costs
+    **O(n²)** in total. This applies to filling an [`ordered_json`](ordered_json.md) object key by key as well as to
+    parsing one, since the parser inserts each key as it is read.
+
+    The cost is negligible for the object sizes typically found in configuration files or API payloads, but it grows
+    steeply for machine-generated objects with many thousands of keys. Measured with `-O2 -DNDEBUG` for parsing a flat
+    object of `n` keys, relative to `#!cpp nlohmann::json` (which uses `#!cpp std::map`):
+
+    | `n`    | `json` | `ordered_json` | factor |
+    |--------|--------|----------------|--------|
+    | 2000   | 0.7 ms | 3.6 ms         | 5×     |
+    | 4000   | 0.8 ms | 14.0 ms        | 19×    |
+    | 8000   | 1.6 ms | 67.8 ms        | 43×    |
+    | 16 000 | 3.3 ms | 181.6 ms       | 54×    |
+
+    If key order matters for objects of that size, consider a container with a lookup index, such as
+    [`tsl::ordered_map`](https://github.com/Tessil/ordered-map)
+    ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)), as the object type -- see
+    [object order](../features/object_order.md).
+
 ## Examples
 
 ??? example

docs/mkdocs/docs/examples/parser_callback_t.cpp

@@ -0,0 +1,47 @@
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // a JSON text with an array and a number inside an object
+    auto text = R"({"IDs": [116, 943], "Width": 800})";
+
+    // discard the array when the parser reads its opening bracket
+    json j_array_start = json::parse(text, [](int /*depth*/, json::parse_event_t event, json & /*parsed*/)
+    {
+        return event != json::parse_event_t::array_start;
+    });
+
+    // discard the same array when the parser reads its closing bracket
+    json j_array_end = json::parse(text, [](int /*depth*/, json::parse_event_t event, json & /*parsed*/)
+    {
+        return event != json::parse_event_t::array_end;
+    });
+
+    // discard the number, but keep its key
+    json j_value = json::parse(text, [](int /*depth*/, json::parse_event_t event, json & parsed)
+    {
+        return !(event == json::parse_event_t::value && parsed == json(800));
+    });
+
+    // discard the key of the number
+    json j_key = json::parse(text, [](int /*depth*/, json::parse_event_t event, json & parsed)
+    {
+        return !(event == json::parse_event_t::key && parsed == json("Width"));
+    });
+
+    // discard the top-level object
+    json j_root = json::parse(text, [](int /*depth*/, json::parse_event_t event, json & /*parsed*/)
+    {
+        return event != json::parse_event_t::object_end;
+    });
+
+    // in every case, the discarded value is removed together with its key
+    std::cout << j_array_start << '\n'
+              << j_array_end << '\n'
+              << j_value << '\n'
+              << j_key << '\n'
+              << j_root << '\n';
+}

docs/mkdocs/docs/examples/parser_callback_t.output

@@ -0,0 +1,5 @@
+{"Width":800}
+{"Width":800}
+{"IDs":[116,943]}
+{"IDs":[116,943]}
+null

docs/mkdocs/docs/features/binary_formats/bson.md

@@ -35,6 +35,19 @@ The library uses the following mapping from JSON values types to BSON types:
     The mapping is **incomplete**, since only JSON-objects (and things contained therein) can be serialized to BSON.
     Also, keys may not contain U+0000, since they are serialized a zero-terminated c-strings.
 
+!!! warning "BSON type 0x11 interoperability"
+
+    The BSON specification defines type `0x11` as a Timestamp. This library uses marker `0x11` when serializing
+    `number_unsigned` values in the range `9223372036854775808..18446744073709551615`. Other BSON implementations may
+    therefore interpret these values as Timestamps instead of unsigned integers.
+
+!!! info "Binary values without a subtype"
+
+    BSON requires every binary value to have a subtype. If a binary value has no subtype, this library serializes it
+    with the generic subtype `0x00`. After deserialization, `has_subtype()` returns `true` and `subtype()` returns `0`.
+    As a result, serializing and deserializing a JSON object containing such a value produces a different JSON object,
+    even though the binary data is unchanged.
+
 ??? example
 
     ```cpp
@@ -82,8 +95,8 @@ The library maps BSON record types to JSON value types as follows:
 
 !!! note "Handling of BSON type 0x11"
 
-    BSON type 0x11 is used to represent uint64 numbers. This library treats these values purely as uint64 numbers 
-    and does not parse them into date-related formats.
+    This library deserializes BSON type `0x11` (Timestamp) as a `number_unsigned` value. The 64-bit value is preserved,
+    but the Timestamp type information is not.
 
 ??? example
 

docs/mkdocs/docs/features/binary_formats/cbor.md

@@ -7,12 +7,12 @@ extremely small code sizes, fairly small message size, and extensibility without
 
     - [CBOR Website](http://cbor.io) - the main source on CBOR
     - [CBOR Playground](http://cbor.me) - an interactive webpage to translate between JSON and CBOR
-    - [RFC 7049](https://tools.ietf.org/html/rfc7049) - the CBOR specification
+    - [RFC 8949](https://www.rfc-editor.org/rfc/rfc8949.html) - the CBOR specification
 
 ## Serialization
 
 The library uses the following mapping from JSON values types to CBOR types according to the CBOR specification
-([RFC 7049](https://www.rfc-editor.org/rfc/rfc7049.html)):
+([RFC 8949](https://www.rfc-editor.org/rfc/rfc8949.html)):
 
 | JSON value type | value/range                                | CBOR type                         | first byte |
 |-----------------|--------------------------------------------|-----------------------------------|------------|

docs/mkdocs/docs/features/conversions.md

@@ -66,8 +66,14 @@ auto t = j.get<std::tuple<double, std::string, int>>();  // {1.0, "hello", 42}
     std::get<1>(refs) = "world";  // modifies j[1] in place
     ```
 
-    A referenced type must be one the library actually stores (or an arithmetic type it can convert to/from);
-    otherwise this is a compile error.
+    A referenced element must name the type the library actually *stores* — one of [`boolean_t`](../api/basic_json/boolean_t.md),
+    [`number_integer_t`](../api/basic_json/number_integer_t.md), [`number_unsigned_t`](../api/basic_json/number_unsigned_t.md),
+    [`number_float_t`](../api/basic_json/number_float_t.md), [`string_t`](../api/basic_json/string_t.md),
+    [`binary_t`](../api/basic_json/binary_t.md), [`array_t`](../api/basic_json/array_t.md), or
+    [`object_t`](../api/basic_json/object_t.md). There is nothing else to refer to, so a reference to any other type is a
+    compile error even when a conversion would exist: `#!cpp std::tuple<int&>` is rejected, because the library stores a
+    `#!cpp number_integer_t` (`#!cpp std::int64_t` by default) and not an `#!cpp int`. This restriction applies only to
+    reference elements — a plain `#!cpp std::tuple<int>` converts by value as usual.
 
 ## Implicit conversions
 
@@ -116,17 +122,34 @@ which forces the explicit `get` form and can catch unintended conversions at com
     with a custom `adl_serializer<std::optional<T>>` specialization. Prefer `get<std::optional<T>>()`/`get_to()`
     over `static_cast` for optional types.
 
-!!! warning "Converting to a fixed-size `std::array` does not check length"
+!!! warning "Converting to a fixed-size destination does not check the array size"
 
-    Converting a JSON array to `#!cpp std::array<T, N>` does not check that the JSON array's size matches `N`:
-    if the JSON array is longer, the extra elements are silently dropped; if it is shorter, the remaining
-    `std::array` elements are left default-constructed. No exception is thrown in either case.
+    Some destination types have a size that is fixed by their C++ type rather than by the JSON value:
+    `#!cpp std::pair<A, B>`, `#!cpp std::tuple<Ts...>`, `#!cpp std::array<T, N>`, C arrays `#!cpp T[N]`, and
+    `#!cpp std::map`/`#!cpp std::unordered_map` with a non-string key type (which is read from an array of
+    two-element arrays). All of them read exactly as many elements as they need via
+    [`at`](../api/basic_json/at.md) and **never compare the JSON array's size to that number**. The two
+    mismatch directions therefore behave differently:
+
+    - The JSON array has **too many** elements: the surplus is **silently discarded**, and no exception is
+      thrown.
+    - The JSON array has **too few** elements: `at` throws
+      [`out_of_range.401`](../home/exceptions.md#jsonexceptionout_of_range401) for the first missing index --
+      an out-of-range error, not a [`type_error`](../home/exceptions.md#type-errors), even though the cause
+      is a shape mismatch.
 
     ```cpp
     json j = {1, 2, 3, 4, 5};
-    auto a = j.get<std::array<int, 3>>();  // {1, 2, 3} -- elements 4 and 5 silently dropped
+
+    auto a = j.get<std::array<int, 3>>();       // {1, 2, 3} -- elements 4 and 5 silently dropped
+    auto p = j.get<std::pair<int, int>>();      // (1, 2)    -- elements 3, 4, and 5 silently dropped
+
+    json k = {1};
+    auto q = k.get<std::pair<int, int>>();      // ❌ throws out_of_range.401
     ```
 
+    If a size mismatch is an error in your application, check the size yourself before converting.
+
 ## Omitting a field when serializing `std::optional`
 
 By default, `to_json` for `std::optional<T>` writes either the value or `#!json null` -- there is no built-in way

docs/mkdocs/docs/features/object_order.md

@@ -53,6 +53,12 @@ If you do want to preserve the **insertion order**, you can use the type [`nlohm
 
 Alternatively, you can use a more sophisticated ordered map like [`tsl::ordered_map`](https://github.com/Tessil/ordered-map) ([integration](https://github.com/nlohmann/json/issues/546#issuecomment-304447518)) or [`nlohmann::fifo_map`](https://github.com/nlohmann/fifo_map) ([integration](https://github.com/nlohmann/json/issues/485#issuecomment-333652309)).
 
+The [`ordered_map`](../api/ordered_map.md) behind `nlohmann::ordered_json` is deliberately minimal and has no lookup
+index, so every key access is a linear scan and building an object of `n` keys costs O(n²). This is unnoticeable at
+typical object sizes but becomes significant for objects with many thousands of keys; see
+[`ordered_map` complexity](../api/ordered_map.md#complexity). The alternatives above keep a lookup index and do not
+have this cost.
+
 ### Notes on parsing
 
 Note that you also need to call the right [`parse`](../api/basic_json/parse.md) function when reading from a file.

docs/mkdocs/docs/features/parsing/index.md

@@ -28,6 +28,22 @@ Inputs consisting of multiple values separated by newlines are handled by the [J
 By default, the library rejects comments and trailing commas. Both can be enabled with parameters of the `parse`
 function — see [comments](../comments.md) and [trailing commas](../trailing_commas.md).
 
+## Strictness and trailing data
+
+[`parse`](../../api/basic_json/parse.md) reads a single JSON value and requires the whole input to be consumed: any
+non-whitespace data after the value is reported as a parse error. Use it when you want to guarantee that an input is
+exactly one complete JSON document.
+
+[`operator>>`](../../api/operator_gtgt.md) follows relaxed `#!cpp std::istream` semantics instead: it parses one JSON
+value and leaves the stream positioned right after it, without requiring the rest of the stream to be consumed. This is
+what makes it possible to read several concatenated values from the same stream, but it also means that "a valid
+document followed by trailing bytes" is accepted rather than rejected. If you are validating conformance, or need to
+reject any input that is not exactly one JSON document, prefer `parse`.
+
+When using `operator>>` to read several concatenated values this way, a value that is a number must be followed by
+whitespace, because `operator>>` consumes the character that terminates a number — see the
+[`operator>>` notes](../../api/operator_gtgt.md#notes) for details and examples.
+
 ## SAX vs. DOM parsing
 
 The library offers two parsing models:

docs/mkdocs/docs/features/parsing/json_lines.md

@@ -49,4 +49,5 @@ JSON Lines input with more than one value is treated as invalid JSON by the [`pa
     with a JSON Lines input does not work, because the parser will try to parse one value after the last one.
 
     This is different from parsing a stream of *concatenated* (non-newline-delimited) JSON values, for which
-    `operator>>` does work -- see its [notes](../../api/operator_gtgt.md#notes) for details.
+    `operator>>` does work, provided that a value that is a number is followed by whitespace -- see its
+    [notes](../../api/operator_gtgt.md#notes) for details.

docs/mkdocs/docs/home/exceptions.md

@@ -291,9 +291,10 @@ A JSON Pointer array index must be a number.
 
 ### json.exception.parse_error.110
 
-When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.
+When parsing a [binary format](../features/binary_formats/index.md), the byte vector ends before the complete value has
+been read.
 
-!!! failure "Example message"
+!!! failure "Example messages"
 
     ```
     [json.exception.parse_error.110] parse error at byte 5: syntax error while parsing CBOR string: unexpected end of input
@@ -301,6 +302,9 @@ When parsing CBOR or MessagePack, the byte vector ends before the complete value
     ```
     [json.exception.parse_error.110] parse error at byte 2: syntax error while parsing UBJSON value: expected end of input; last byte: 0x5A
     ```
+    ```
+    [json.exception.parse_error.110] parse error at byte 8: syntax error while parsing BSON number: unexpected end of input
+    ```
 
 ### json.exception.parse_error.112
 
@@ -329,10 +333,14 @@ An unexpected byte was read in a [binary format](../features/binary_formats/inde
     ```
     [json.exception.parse_error.112] parse error at byte 9: syntax error while parsing CBOR value: negative integer overflow
     ```
+    ```
+    [json.exception.parse_error.112] parse error at byte 5: syntax error while parsing BSON document: document size 6 does not match the number of bytes read (5)
+    ```
 
 ### json.exception.parse_error.113
 
-While parsing a map key, a value that is not a string has been read.
+A string could not be read from a [binary format](../features/binary_formats/index.md): either a value that is not a
+string was read where one was required (for instance as a map key), or the string's length specification is invalid.
 
 !!! failure "Example messages"
 
@@ -345,6 +353,9 @@ While parsing a map key, a value that is not a string has been read.
     ```
     [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing UBJSON char: byte after 'C' must be in range 0x00..0x7F; last byte: 0x82
     ```
+    ```
+    [json.exception.parse_error.113] parse error at byte 3: syntax error while parsing BJData string: string length must not be negative
+    ```
 
 ### json.exception.parse_error.114
 
@@ -853,13 +864,21 @@ and this exception no longer occurs.
 
 ### json.exception.out_of_range.408
 
-The size (following `#`) of an UBJSON array or object exceeds the maximal capacity.
+The size of an array or object in a [binary format](../features/binary_formats/index.md) exceeds the maximal capacity:
+the size following `#` for [UBJSON](../features/binary_formats/ubjson.md)/[BJData](../features/binary_formats/bjdata.md),
+or the encoded length for [CBOR](../features/binary_formats/cbor.md).
 
-!!! failure "Example message"
+!!! failure "Example messages"
 
     ```
     excessive array size: 8658170730974374167
     ```
+    ```
+    [json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive array size
+    ```
+    ```
+    [json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive map size
+    ```
 
 ### json.exception.out_of_range.409
 

docs/mkdocs/mkdocs.yml

@@ -296,6 +296,7 @@ nav:
           - 'JSON_USE_GLOBAL_UDLS': api/macros/json_use_global_udls.md
           - 'JSON_USE_IMPLICIT_CONVERSIONS': api/macros/json_use_implicit_conversions.md
           - 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
+          - 'JSON_USE_SIMDUTF': api/macros/json_use_simdutf.md
           - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
           - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_intrusive.md
           - 'NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_non_intrusive.md

include/nlohmann/detail/input/binary_reader.hpp

@@ -197,7 +197,10 @@ class binary_reader
     {
         const std::size_t document_start = chars_read;
         std::int32_t document_size{};
-        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+        if (!get_number<std::int32_t, true>(input_format_t::bson, document_size))
+        {
+            return false;
+        }
 
         if (JSON_HEDLEY_UNLIKELY(!sax->start_object(detail::unknown_size())))
         {
@@ -287,7 +290,10 @@ class binary_reader
 
         // All BSON binary values have a subtype
         std::uint8_t subtype{};
-        get_number<std::uint8_t>(input_format_t::bson, subtype);
+        if (JSON_HEDLEY_UNLIKELY(!get_number<std::uint8_t>(input_format_t::bson, subtype)))
+        {
+            return false;
+        }
         result.set_subtype(subtype);
 
         return get_binary(input_format_t::bson, len, result);
@@ -340,7 +346,8 @@ class binary_reader
 
             case 0x08: // boolean
             {
-                return sax->boolean(get() != 0);
+                std::uint8_t value{};
+                return get_number<std::uint8_t>(input_format_t::bson, value) && sax->boolean(value != 0);
             }
 
             case 0x0A: // null
@@ -431,7 +438,10 @@ class binary_reader
     {
         const std::size_t document_start = chars_read;
         std::int32_t document_size{};
-        get_number<std::int32_t, true>(input_format_t::bson, document_size);
+        if (!get_number<std::int32_t, true>(input_format_t::bson, document_size))
+        {
+            return false;
+        }
 
         if (JSON_HEDLEY_UNLIKELY(!sax->start_array(detail::unknown_size())))
         {
@@ -694,13 +704,15 @@ class binary_reader
             case 0x9A: // array (four-byte uint32_t for n follow)
             {
                 std::uint32_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_array(conditional_static_cast<std::size_t>(len), tag_handler);
+                std::size_t size{};
+                return get_number(input_format_t::cbor, len) && get_cbor_container_size(len, size, "array") && get_cbor_array(size, tag_handler);
             }
 
             case 0x9B: // array (eight-byte uint64_t for n follow)
             {
                 std::uint64_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_array(conditional_static_cast<std::size_t>(len), tag_handler);
+                std::size_t size{};
+                return get_number(input_format_t::cbor, len) && get_cbor_container_size(len, size, "array") && get_cbor_array(size, tag_handler);
             }
 
             case 0x9F: // array (indefinite length)
@@ -748,13 +760,15 @@ class binary_reader
             case 0xBA: // map (four-byte uint32_t for n follow)
             {
                 std::uint32_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_object(conditional_static_cast<std::size_t>(len), tag_handler);
+                std::size_t size{};
+                return get_number(input_format_t::cbor, len) && get_cbor_container_size(len, size, "map") && get_cbor_object(size, tag_handler);
             }
 
             case 0xBB: // map (eight-byte uint64_t for n follow)
             {
                 std::uint64_t len{};
-                return get_number(input_format_t::cbor, len) && get_cbor_object(conditional_static_cast<std::size_t>(len), tag_handler);
+                std::size_t size{};
+                return get_number(input_format_t::cbor, len) && get_cbor_container_size(len, size, "map") && get_cbor_object(size, tag_handler);
             }
 
             case 0xBF: // map (indefinite length)
@@ -797,25 +811,37 @@ class binary_reader
                             case 0xD8:
                             {
                                 std::uint8_t subtype_to_ignore{};
-                                get_number(input_format_t::cbor, subtype_to_ignore);
+                                if (!get_number(input_format_t::cbor, subtype_to_ignore))
+                                {
+                                    return false;
+                                }
                                 break;
                             }
                             case 0xD9:
                             {
                                 std::uint16_t subtype_to_ignore{};
-                                get_number(input_format_t::cbor, subtype_to_ignore);
+                                if (!get_number(input_format_t::cbor, subtype_to_ignore))
+                                {
+                                    return false;
+                                }
                                 break;
                             }
                             case 0xDA:
                             {
                                 std::uint32_t subtype_to_ignore{};
-                                get_number(input_format_t::cbor, subtype_to_ignore);
+                                if (!get_number(input_format_t::cbor, subtype_to_ignore))
+                                {
+                                    return false;
+                                }
                                 break;
                             }
                             case 0xDB:
                             {
                                 std::uint64_t subtype_to_ignore{};
-                                get_number(input_format_t::cbor, subtype_to_ignore);
+                                if (!get_number(input_format_t::cbor, subtype_to_ignore))
+                                {
+                                    return false;
+                                }
                                 break;
                             }
                             default:
@@ -833,28 +859,40 @@ class binary_reader
                             case 0xD8:
                             {
                                 std::uint8_t subtype{};
-                                get_number(input_format_t::cbor, subtype);
+                                if (!get_number(input_format_t::cbor, subtype))
+                                {
+                                    return false;
+                                }
                                 b.set_subtype(detail::conditional_static_cast<typename binary_t::subtype_type>(subtype));
                                 break;
                             }
                             case 0xD9:
                             {
                                 std::uint16_t subtype{};
-                                get_number(input_format_t::cbor, subtype);
+                                if (!get_number(input_format_t::cbor, subtype))
+                                {
+                                    return false;
+                                }
                                 b.set_subtype(detail::conditional_static_cast<typename binary_t::subtype_type>(subtype));
                                 break;
                             }
                             case 0xDA:
                             {
                                 std::uint32_t subtype{};
-                                get_number(input_format_t::cbor, subtype);
+                                if (!get_number(input_format_t::cbor, subtype))
+                                {
+                                    return false;
+                                }
                                 b.set_subtype(detail::conditional_static_cast<typename binary_t::subtype_type>(subtype));
                                 break;
                             }
                             case 0xDB:
                             {
                                 std::uint64_t subtype{};
-                                get_number(input_format_t::cbor, subtype);
+                                if (!get_number(input_format_t::cbor, subtype))
+                                {
+                                    return false;
+                                }
                                 b.set_subtype(detail::conditional_static_cast<typename binary_t::subtype_type>(subtype));
                                 break;
                             }
@@ -896,7 +934,7 @@ class binary_reader
                 const auto byte1 = static_cast<unsigned char>(byte1_raw);
                 const auto byte2 = static_cast<unsigned char>(byte2_raw);
 
-                // Code from RFC 7049, Appendix D, Figure 3:
+                // Code from RFC 8949, Appendix D, Figure 3:
                 // As half-precision floating-point numbers were only added
                 // to IEEE 754 in 2008, today's programming platforms often
                 // still only have limited support for them. It is very
@@ -909,8 +947,8 @@ class binary_reader
                 {
                     const int exp = (half >> 10u) & 0x1Fu;
                     const unsigned int mant = half & 0x3FFu;
-                    JSON_ASSERT(0 <= exp&& exp <= 32);
-                    JSON_ASSERT(mant <= 1024);
+                    JSON_ASSERT(exp <= 31);
+                    JSON_ASSERT(mant <= 1023);
                     switch (exp)
                     {
                         case 0:
@@ -1145,6 +1183,31 @@ class binary_reader
         }
     }
 
+    /*!
+    @brief narrow a definite CBOR array/map length to std::size_t
+
+    A definite length is rejected if it does not fit in std::size_t or if it
+    equals detail::unknown_size(), which is reserved to mark an indefinite-
+    length container and would otherwise make the length read as indefinite.
+    Both cases exceed any container's max_size(), so no representable input
+    is affected.
+
+    @param[in]  len      the declared length
+    @param[out] result   the length narrowed to std::size_t
+    @param[in]  context  "array" or "map", for the error message
+    @return whether the length is usable
+    */
+    bool get_cbor_container_size(const std::uint64_t len, std::size_t& result, const char* context)
+    {
+        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::size_t>(len) || len == detail::unknown_size()))
+        {
+            return sax->parse_error(chars_read, get_token_string(), out_of_range::create(408,
+                                    exception_message(input_format_t::cbor, concat("excessive ", context, " size"), "size"), nullptr));
+        }
+        result = conditional_static_cast<std::size_t>(len);
+        return true;
+    }
+
     /*!
     @param[in] len  the length of the array or detail::unknown_size() for an
                     array of indefinite size
@@ -2484,7 +2547,7 @@ class binary_reader
                 const auto byte1 = static_cast<unsigned char>(byte1_raw);
                 const auto byte2 = static_cast<unsigned char>(byte2_raw);
 
-                // Code from RFC 7049, Appendix D, Figure 3:
+                // Code from RFC 8949, Appendix D, Figure 3:
                 // As half-precision floating-point numbers were only added
                 // to IEEE 754 in 2008, today's programming platforms often
                 // still only have limited support for them. It is very
@@ -2497,8 +2560,8 @@ class binary_reader
                 {
                     const int exp = (half >> 10u) & 0x1Fu;
                     const unsigned int mant = half & 0x3FFu;
-                    JSON_ASSERT(0 <= exp&& exp <= 32);
-                    JSON_ASSERT(mant <= 1024);
+                    JSON_ASSERT(exp <= 31);
+                    JSON_ASSERT(mant <= 1023);
                     switch (exp)
                     {
                         case 0:
@@ -2815,7 +2878,17 @@ class binary_reader
             case token_type::value_unsigned:
                 return sax->number_unsigned(number_lexer.get_number_unsigned());
             case token_type::value_float:
-                return sax->number_float(number_lexer.get_number_float(), std::move(number_string));
+            {
+                const auto parsed_float = number_lexer.get_number_float();
+                if (JSON_HEDLEY_UNLIKELY(!std::isfinite(parsed_float)))
+                {
+                    return sax->parse_error(
+                               chars_read,
+                               number_string,
+                               out_of_range::create(406, concat("number overflow parsing '", number_string, '\''), nullptr));
+                }
+                return sax->number_float(parsed_float, std::move(number_string));
+            }
             case token_type::uninitialized:
             case token_type::literal_true:
             case token_type::literal_false:

include/nlohmann/detail/input/input_adapters.hpp

@@ -231,6 +231,33 @@ class iterator_input_adapter
         std::is_same<IteratorType, SentinelType>::value && std::is_pointer<IteratorType>::value;
 #endif
 
+  public:
+    // Whether the remaining input is a single contiguous block of 1-byte
+    // elements that the lexer can inspect directly (used for the SWAR string
+    // fast path). Restricted to same-type iterator/sentinel pairs so that plain
+    // std::distance/std::advance are well-defined in all standards.
+    static constexpr bool supports_bulk_scan =
+        iterator_is_contiguous && std::is_same<IteratorType, SentinelType>::value && sizeof(char_type) == 1;
+
+    // Pointer to the next unread element; only valid when bulk_remaining() > 0.
+    const char_type* bulk_data() const
+    {
+        return &*current;
+    }
+
+    // Number of unread elements available as one contiguous block.
+    std::size_t bulk_remaining() const
+    {
+        return static_cast<std::size_t>(std::distance(current, end));
+    }
+
+    // Consume @a n elements previously inspected via bulk_data().
+    void bulk_skip(std::size_t n)
+    {
+        std::advance(current, static_cast<typename std::iterator_traits<IteratorType>::difference_type>(n));
+    }
+
+  private:
     // contiguous fast path: bulk copy the remaining range with std::memcpy
     template<class T>
     std::size_t get_elements_impl(T* dest, std::size_t count, std::true_type /*contiguous*/)
@@ -566,6 +593,24 @@ typename iterator_input_adapter_factory<IteratorType, SentinelType>::adapter_typ
     return factory_type::create(first, last);
 }
 
+// Detect a container that stores its elements contiguously as single bytes
+// (std::string, std::vector<char/unsigned char>, std::array<char, N>,
+// std::string_view, ...). Such inputs are wrapped in a pointer-based adapter so
+// they benefit from the contiguous fast paths (bulk string scanning, memcpy for
+// binary formats) in every C++ standard - not only in C++20, where the standard
+// library iterators model std::contiguous_iterator and are detected directly.
+template<typename ContainerType, typename = void>
+struct is_contiguous_byte_container : std::false_type {};
+
+template<typename ContainerType>
+struct is_contiguous_byte_container < ContainerType, void_t <
+decltype(std::declval<const ContainerType&>().data()),
+decltype(std::declval<const ContainerType&>().size()) >>
+            : std::integral_constant < bool,
+        std::is_pointer<decltype(std::declval<const ContainerType&>().data())>::value&&
+        std::is_integral<typename std::remove_pointer<decltype(std::declval<const ContainerType&>().data())>::type>::value&&
+        sizeof(typename std::remove_pointer<decltype(std::declval<const ContainerType&>().data())>::type) == 1 > {};
+
 // Convenience shorthand from container to iterator
 // Enables ADL on begin(container) and end(container)
 // Encloses the using declarations in namespace for not to leak them to outside scope
@@ -593,12 +638,32 @@ struct container_input_adapter_factory< ContainerType,
 
 }  // namespace container_input_adapter_factory_impl
 
-template<typename ContainerType>
-typename container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::adapter_type input_adapter(ContainerType&& container)
+// General container path (iterator-based). Contiguous single-byte containers
+// are excluded here and routed through the pointer-based overload below.
+template < typename ContainerType,
+           enable_if_t < !is_contiguous_byte_container<ContainerType>::value, int > = 0 >
+typename container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::adapter_type input_adapter(ContainerType && container)
 {
     return container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::create(std::forward<ContainerType>(container));
 }
 
+// Contiguous single-byte containers (std::string, std::vector<char>, ...) are
+// wrapped in a pointer-based adapter so the contiguous fast paths apply in every
+// standard. The pointer keeps the container's own element type (const char* for
+// std::string, const std::uint8_t* for std::vector<std::uint8_t>, ...), so the
+// resulting char_type - and therefore the parsing behavior - is byte-for-byte
+// identical to the iterator-based path; only the raw pointer additionally
+// enables the bulk fast paths. The container outlives the adapter for the whole
+// parse (temporaries live until the end of the full expression), exactly as the
+// iterators it replaces did.
+template < typename ContainerType,
+           enable_if_t < is_contiguous_byte_container<ContainerType>::value, int > = 0 >
+auto input_adapter(const ContainerType& container)
+-> decltype(input_adapter(container.data(), container.data() + container.size()))
+{
+    return input_adapter(container.data(), container.data() + container.size());
+}
+
 // specialization for std::string
 using string_input_adapter_type = decltype(input_adapter(std::declval<std::string>()));
 

include/nlohmann/detail/input/json_sax.hpp

@@ -626,14 +626,7 @@ class json_sax_dom_callback_parser
         if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_structured())
         {
             // remove discarded value
-            for (auto it = ref_stack.back()->begin(); it != ref_stack.back()->end(); ++it)
-            {
-                if (it->is_discarded())
-                {
-                    ref_stack.back()->erase(it);
-                    break;
-                }
-            }
+            remove_discarded_value(*ref_stack.back());
         }
 
         return true;
@@ -674,8 +667,9 @@ class json_sax_dom_callback_parser
     bool end_array()
     {
         bool keep = true;
+        const bool stored = ref_stack.back() != nullptr;
 
-        if (ref_stack.back())
+        if (stored)
         {
             keep = callback(static_cast<int>(ref_stack.size()) - 1, parse_event_t::array_end, *ref_stack.back());
             if (keep)
@@ -709,9 +703,19 @@ class json_sax_dom_callback_parser
         keep_stack.pop_back();
 
         // remove discarded value
-        if (!keep && !ref_stack.empty() && ref_stack.back()->is_array())
+        if (!ref_stack.empty() && ref_stack.back())
         {
-            ref_stack.back()->m_data.m_value.array->pop_back();
+            if (!keep && ref_stack.back()->is_array())
+            {
+                ref_stack.back()->m_data.m_value.array->pop_back();
+            }
+            else if ((!keep || !stored) && ref_stack.back()->is_object())
+            {
+                // the array is either still stored under its key or was never
+                // stored, leaving the placeholder key() wrote; both show up as
+                // a discarded member of the parent object
+                remove_discarded_value(*ref_stack.back());
+            }
         }
 
         return true;
@@ -801,6 +805,19 @@ class json_sax_dom_callback_parser
     }
 #endif
 
+    /// remove the discarded value the callback rejected from its parent
+    static void remove_discarded_value(BasicJsonType& parent)
+    {
+        for (auto it = parent.begin(); it != parent.end(); ++it)
+        {
+            if (it->is_discarded())
+            {
+                parent.erase(it);
+                break;
+            }
+        }
+    }
+
     /*!
     @param[in] v  value to add to the JSON value we build during parsing
     @param[in] skip_callback  whether we should skip calling the callback
@@ -841,6 +858,18 @@ class json_sax_dom_callback_parser
         // do not handle this value if we just learnt it shall be discarded
         if (!keep)
         {
+            // if the value was to become an object member, key() already
+            // stored a placeholder for it that has to be removed again
+            if (!ref_stack.empty() && ref_stack.back() && ref_stack.back()->is_object())
+            {
+                JSON_ASSERT(!key_keep_stack.empty());
+                const bool placeholder_stored = key_keep_stack.back();
+                key_keep_stack.pop_back();
+                if (placeholder_stored)
+                {
+                    remove_discarded_value(*ref_stack.back());
+                }
+            }
             return {false, nullptr};
         }
 

include/nlohmann/detail/input/lexer.hpp

@@ -19,7 +19,9 @@
 #include <vector> // vector
 
 #include <nlohmann/detail/input/input_adapters.hpp>
+#include <nlohmann/detail/input/number_parse.hpp>
 #include <nlohmann/detail/input/position_t.hpp>
+#include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
 
@@ -125,6 +127,25 @@ constexpr bool input_adapter_supports_seek(std::false_type /*detected*/)
     return false;
 }
 
+// Detect whether an input adapter exposes a contiguous byte block that the
+// lexer can scan directly (see iterator_input_adapter::supports_bulk_scan).
+// Adapters without the flag - file, stream, wide-string, user-defined - fall
+// back to the character-at-a-time string scanner.
+template<typename InputAdapterType>
+using detect_supports_bulk_scan = decltype(InputAdapterType::supports_bulk_scan);
+
+template<typename InputAdapterType>
+constexpr bool input_adapter_supports_bulk_scan(std::true_type /*detected*/)
+{
+    return InputAdapterType::supports_bulk_scan;
+}
+
+template<typename InputAdapterType>
+constexpr bool input_adapter_supports_bulk_scan(std::false_type /*detected*/)
+{
+    return false;
+}
+
 /*!
 @brief lexical analysis
 
@@ -146,6 +167,14 @@ class lexer : public lexer_base<BasicJsonType>
     static constexpr bool lazy_token_string =
         input_adapter_supports_seek<InputAdapterType>(is_detected<detect_supports_seek, InputAdapterType> {});
 
+    /// whether string scanning may bulk-consume runs of ordinary characters
+    /// directly from a contiguous input buffer (SWAR fast path). This requires
+    /// the token to be reconstructible lazily (lazy_token_string), so bypassing
+    /// the per-character capture in get() cannot lose error diagnostics.
+    static constexpr bool bulk_scan =
+        lazy_token_string
+        && input_adapter_supports_bulk_scan<InputAdapterType>(is_detected<detect_supports_bulk_scan, InputAdapterType> {});
+
   public:
     using token_type = typename lexer_base<BasicJsonType>::token_type;
 
@@ -265,6 +294,40 @@ class lexer : public lexer_base<BasicJsonType>
         return true;
     }
 
+    /// contiguous input: bulk-append the run of ordinary characters and complete
+    /// well-formed UTF-8 sequences starting at the current read position, leaving
+    /// the first byte that needs individual handling (the closing quote, an
+    /// escape, a control character, or an ill-formed UTF-8 byte) for get()
+    void scan_string_bulk(std::true_type /*bulk*/)
+    {
+        // a pending unget must be consumed through the normal path first
+        if (next_unget)
+        {
+            return;
+        }
+        const std::size_t remaining = ia.bulk_remaining();
+        if (remaining == 0)
+        {
+            return;
+        }
+        const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
+
+        const std::size_t pos = string_bulk_run(data, remaining);
+        if (pos == 0)
+        {
+            return;
+        }
+        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), pos);
+        ia.bulk_skip(pos);
+        // the run contains no newline (all bytes < 0x20 are treated as special),
+        // so only the flat character counters advance
+        position.chars_read_total += pos;
+        position.chars_read_current_line += pos;
+    }
+
+    /// streaming input: no bulk fast path
+    void scan_string_bulk(std::false_type /*bulk*/) const noexcept {}
+
     /*!
     @brief scan a string literal
 
@@ -290,6 +353,10 @@ class lexer : public lexer_base<BasicJsonType>
 
         while (true)
         {
+            // bulk-consume ordinary characters from contiguous input, then
+            // handle the next special byte through the switch below
+            scan_string_bulk(std::integral_constant<bool, bulk_scan> {});
+
             // get the next character
             switch (get())
             {
@@ -1279,45 +1346,56 @@ scan_number_done:
         // we are done scanning a number)
         unget();
 
-        char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-        errno = 0;
+        return convert_number(number_type);
+    }
 
-        // try to parse integers first and fall back to floats
+    /*!
+    @brief convert the number text in token_buffer to its value and token type
+
+    The digit sequence in token_buffer has already been validated (by the
+    scan_number() state machine or by the contiguous fast path) and holds the
+    locale decimal point in place of '.'. Integers are parsed first and fall
+    back to floating point on overflow. This is shared so both scanners produce
+    identical results.
+    */
+    token_type convert_number(token_type number_type)
+    {
+        const char* const num_begin = token_buffer.data();
+        const char* const num_end = num_begin + token_buffer.size();
+
+        // try to parse integers first and fall back to floats; the digit
+        // sequence has already been validated, so a dedicated parser can avoid
+        // the locale/errno overhead of strtoull
         if (number_type == token_type::value_unsigned)
         {
-            const auto x = std::strtoull(token_buffer.data(), &endptr, 10);
-
-            // we checked the number format before
-            JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
-
-            if (errno != ERANGE)
+            if (parse_integer_unsigned(num_begin, num_end, value_unsigned))
             {
-                value_unsigned = static_cast<number_unsigned_t>(x);
-                if (value_unsigned == x)
-                {
-                    return token_type::value_unsigned;
-                }
+                return token_type::value_unsigned;
             }
         }
         else if (number_type == token_type::value_integer)
         {
-            const auto x = std::strtoll(token_buffer.data(), &endptr, 10);
-
-            // we checked the number format before
-            JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
-
-            if (errno != ERANGE)
+            if (parse_integer_signed(num_begin, num_end, value_integer))
             {
-                value_integer = static_cast<number_integer_t>(x);
-                if (value_integer == x)
-                {
-                    return token_type::value_integer;
-                }
+                return token_type::value_integer;
             }
         }
 
         // this code is reached if we parse a floating-point number or if an
-        // integer conversion above failed
+        // integer conversion above overflowed. Prefer std::from_chars
+        // (Eisel-Lemire, locale-independent, correctly rounded) when available;
+        // otherwise the exact Clinger fast path (double only); otherwise the
+        // locale-aware strtof/strtod.
+        if (parse_float_from_chars(num_begin, num_end, value_float))
+        {
+            return token_type::value_float;
+        }
+        if (parse_float_fast(num_begin, num_end, decimal_point_char, value_float))
+        {
+            return token_type::value_float;
+        }
+
+        char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
         strtof(value_float, token_buffer.data(), &endptr);
 
         // we checked the number format before
@@ -1326,6 +1404,130 @@ scan_number_done:
         return token_type::value_float;
     }
 
+    /*!
+    @brief contiguous fast path for scanning a number
+
+    Parses the whole number token straight from the input buffer, avoiding the
+    per-character get()/add() of scan_number(). On success it fills token_buffer
+    (with the locale decimal point substituted, as scan_number() does) and
+    returns the token type. On anything it does not fully recognize as a
+    well-formed number it makes no state change and returns
+    token_type::uninitialized, so the caller falls back to scan_number(), which
+    then produces the exact diagnostic. @a current is the first digit or the
+    leading minus (already read); the remaining bytes are taken from the adapter.
+    */
+    token_type scan_number_bulk_contiguous()
+    {
+        // a pending unget offsets the buffer position from current; fall back
+        if (next_unget)
+        {
+            return token_type::uninitialized;
+        }
+        const std::size_t rem = ia.bulk_remaining();
+        if (rem == 0)
+        {
+            // the first digit is the last input byte; let scan_number() finish
+            return token_type::uninitialized;
+        }
+        // the byte before the next unread one is current (contiguous input)
+        const char* const data = reinterpret_cast<const char*>(ia.bulk_data()) - 1;
+        const std::size_t avail = rem + 1;
+
+        // validate + classify the number extent (mirrors scan_number()'s grammar)
+        std::size_t i = 0;
+        std::size_t dot_index = std::string::npos;
+        token_type number_type = token_type::value_unsigned;
+        if (data[0] == '-')
+        {
+            number_type = token_type::value_integer;
+            i = 1;
+            if (i >= avail)
+            {
+                return token_type::uninitialized;
+            }
+        }
+        if (data[i] == '0')
+        {
+            ++i;
+        }
+        else if (data[i] >= '1' && data[i] <= '9')
+        {
+            ++i;
+            while (i < avail && data[i] >= '0' && data[i] <= '9')
+            {
+                ++i;
+            }
+        }
+        else
+        {
+            return token_type::uninitialized;
+        }
+        if (i < avail && data[i] == '.')
+        {
+            number_type = token_type::value_float;
+            dot_index = i;
+            ++i;
+            if (i >= avail || !(data[i] >= '0' && data[i] <= '9'))
+            {
+                return token_type::uninitialized;
+            }
+            while (i < avail && data[i] >= '0' && data[i] <= '9')
+            {
+                ++i;
+            }
+        }
+        if (i < avail && (data[i] == 'e' || data[i] == 'E'))
+        {
+            number_type = token_type::value_float;
+            ++i;
+            if (i < avail && (data[i] == '+' || data[i] == '-'))
+            {
+                ++i;
+            }
+            if (i >= avail || !(data[i] >= '0' && data[i] <= '9'))
+            {
+                return token_type::uninitialized;
+            }
+            while (i < avail && data[i] >= '0' && data[i] <= '9')
+            {
+                ++i;
+            }
+        }
+        const std::size_t len = i;
+
+        // materialize the token exactly as scan_number() would, substituting the
+        // locale decimal point so convert_number()'s strtof fallback stays valid.
+        // reset() already cleared token_buffer, so append() fills it (assign() is
+        // avoided because custom string_t types need not provide it)
+        reset();
+        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), len);
+        if (dot_index != std::string::npos)
+        {
+            token_buffer[dot_index] = static_cast<typename string_t::value_type>(decimal_point_char);
+            decimal_point_position = dot_index;
+        }
+
+        // consume the remaining bytes of the number (current was already read)
+        ia.bulk_skip(len - 1);
+        position.chars_read_total += (len - 1);
+        position.chars_read_current_line += (len - 1);
+
+        return convert_number(number_type);
+    }
+
+    /// contiguous input: try the number fast path, else the byte-path scanner
+    token_type scan_number_dispatch(std::true_type /*bulk*/)
+    {
+        const token_type t = scan_number_bulk_contiguous();
+        return (t != token_type::uninitialized) ? t : scan_number();
+    }
+
+    /// streaming input: always use the byte-path scanner
+    token_type scan_number_dispatch(std::false_type /*bulk*/)
+    {
+        return scan_number();
+    }
+
     /*!
     @param[in] literal_text  the literal text to expect
     @param[in] length        the length of the passed literal text
@@ -1680,7 +1882,7 @@ scan_number_done:
             case '7':
             case '8':
             case '9':
-                return scan_number();
+                return scan_number_dispatch(std::integral_constant<bool, bulk_scan> {});
 
             // end of input (the null byte is needed when parsing from
             // string literals)

include/nlohmann/detail/input/number_parse.hpp

@@ -0,0 +1,302 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <array> // array
+#include <cfloat> // FLT_EVAL_METHOD
+#include <cstddef> // size_t
+#include <cstdint> // int64_t, uint64_t
+#include <limits> // numeric_limits
+
+#include <nlohmann/detail/macro_scope.hpp>
+
+// std::from_chars lives in <charconv>, but being in C++17 mode does not
+// guarantee the header exists: GCC 7 sets __cplusplus to C++17 yet ships no
+// <charconv> (added in GCC 8; floating-point support in GCC 11). Guard the
+// include with __has_include so such toolchains fall back to the scalar path.
+#if defined(JSON_HAS_CPP_17) && defined(__has_include)
+    #if __has_include(<charconv>)
+        #include <charconv> // from_chars (only used when __cpp_lib_to_chars is defined)
+        #include <system_error> // errc
+    #endif
+#endif
+
+// This file contains the value-conversion helpers used by the lexer to turn an
+// already-validated number token into a value, without the locale/errno
+// overhead of std::strtoull/std::strtod. They are free functions so the lexer
+// stays focused on scanning; see lexer::convert_number().
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+/*!
+@brief fast integer parser for an already-validated unsigned integer
+
+The number scanner has already checked that [first, last) is a valid JSON
+integer, so this only needs to accumulate the digits and detect overflow. This
+avoids the locale/errno machinery of std::strtoull, which dominates
+integer-heavy inputs.
+
+@param[in]  first   pointer to the first character (a digit)
+@param[in]  last    pointer past the last character
+@param[out] value   the parsed value on success
+@return true if the value fit into @a NumberUnsignedType; false on overflow, in
+        which case the caller falls back to floating-point parsing (matching the
+        previous std::strtoull behavior)
+*/
+template<typename NumberUnsignedType>
+bool parse_integer_unsigned(const char* first, const char* last, NumberUnsignedType& value) noexcept
+{
+    // accumulate in the widest unsigned type used by the previous strtoull
+    // path so the overflow behavior is unchanged for custom number types
+    std::uint64_t x = 0;
+    constexpr std::uint64_t cutoff = (std::numeric_limits<std::uint64_t>::max)() / 10u;
+    constexpr std::uint64_t cutlim = (std::numeric_limits<std::uint64_t>::max)() % 10u;
+    for (const char* p = first; p != last; ++p)
+    {
+        const auto digit = static_cast<std::uint64_t>(static_cast<unsigned char>(*p) - static_cast<unsigned char>('0'));
+        if (JSON_HEDLEY_UNLIKELY(x > cutoff || (x == cutoff && digit > cutlim)))
+        {
+            return false;
+        }
+        x = (x * 10u) + digit;
+    }
+    value = static_cast<NumberUnsignedType>(x);
+    // reject values that do not round-trip into a narrower NumberUnsignedType
+    return static_cast<std::uint64_t>(value) == x;
+}
+
+/*!
+@brief fast integer parser for an already-validated negative integer
+
+@param[in]  first   pointer to the leading '-'
+@param[in]  last    pointer past the last character
+@param[out] value   the parsed (negative) value on success
+@return true on success; false on overflow (caller falls back to float)
+*/
+template<typename NumberIntegerType>
+bool parse_integer_signed(const char* first, const char* last, NumberIntegerType& value) noexcept
+{
+    // the state machine only reaches the signed path via a leading '-'
+    JSON_ASSERT(first != last && *first == '-');
+    std::uint64_t magnitude = 0;
+    // |INT64_MIN| == INT64_MAX + 1; this is the largest admissible magnitude
+    constexpr std::uint64_t limit = static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()) + 1u;
+    for (const char* p = first + 1; p != last; ++p)
+    {
+        const auto digit = static_cast<std::uint64_t>(static_cast<unsigned char>(*p) - static_cast<unsigned char>('0'));
+        if (JSON_HEDLEY_UNLIKELY(magnitude > (limit - digit) / 10u))
+        {
+            return false;
+        }
+        magnitude = (magnitude * 10u) + digit;
+    }
+    const std::int64_t x = (magnitude == limit)
+                           ? (std::numeric_limits<std::int64_t>::min)()
+                           : -static_cast<std::int64_t>(magnitude);
+    value = static_cast<NumberIntegerType>(x);
+    // reject values that do not round-trip into a narrower NumberIntegerType
+    return static_cast<std::int64_t>(value) == x;
+}
+
+/*!
+@brief exact fast path for parsing a `double` (Clinger's algorithm)
+
+For the common case - at most 19 significant digits, a decimal exponent in
+[-22, 22], and a significand below 2^53 - the value equals significand *
+10^exp computed in IEEE-754 double arithmetic, which is exact under
+round-to-nearest because both operands are exactly representable. This is the
+same fast path used by fast_float/simdjson; the general cases are left to
+std::strtod. The parser only activates for number_float_t == double; float and
+long double keep the std::strtof/std::strtold paths (see the templated overload
+below).
+
+@param[in]  first          pointer to the first character of the number
+@param[in]  last           pointer past the last character
+@param[in]  decimal_point  the (locale-dependent) decimal point character
+@param[out] out            the parsed value on success
+@return true if the value was parsed exactly; false to fall back to strtod
+*/
+template<typename DecimalPointType>
+bool parse_float_fast(const char* first, const char* last, DecimalPointType decimal_point, double& out) noexcept
+{
+#if defined(FLT_EVAL_METHOD) && FLT_EVAL_METHOD != 0
+    // Clinger's fast path is only exact when double operations are evaluated in
+    // true double precision. On platforms that keep intermediates in extended
+    // precision (e.g. the x87 FPU on 32-bit x86, where FLT_EVAL_METHOD == 2) the
+    // single significand * 10^scale step is double-rounded and can be 1 ULP off,
+    // so decline and let the caller fall back to the correctly-rounded
+    // std::from_chars / std::strtod path.
+    static_cast<void>(first);
+    static_cast<void>(last);
+    static_cast<void>(decimal_point);
+    static_cast<void>(out);
+    return false;
+#else
+    static const std::array<double, 23> powers_of_ten =
+    {
+        {
+            1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11,
+            1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22
+        }
+    };
+
+    const char* p = first;
+    bool negative = false;
+    if (p != last && (*p == '-' || *p == '+'))
+    {
+        negative = (*p == '-');
+        ++p;
+    }
+
+    std::uint64_t significand = 0;
+    int num_digits = 0;
+    int fractional_digits = 0;
+    bool seen_dot = false;
+    bool any_digit = false;
+    for (; p != last; ++p)
+    {
+        const char c = *p;
+        if (c >= '0' && c <= '9')
+        {
+            any_digit = true;
+            if (JSON_HEDLEY_UNLIKELY(num_digits >= 19))
+            {
+                return false; // significand may not fit into uint64_t
+            }
+            significand = (significand * 10u) + static_cast<std::uint64_t>(c - '0');
+            ++num_digits;
+            fractional_digits += static_cast<int>(seen_dot);
+        }
+        else if (static_cast<DecimalPointType>(c) == decimal_point)
+        {
+            if (JSON_HEDLEY_UNLIKELY(seen_dot))
+            {
+                return false;
+            }
+            seen_dot = true;
+        }
+        else if (c == 'e' || c == 'E')
+        {
+            ++p;
+            break;
+        }
+        else
+        {
+            return false;
+        }
+    }
+    if (JSON_HEDLEY_UNLIKELY(!any_digit))
+    {
+        return false;
+    }
+
+    int exponent = 0;
+    if (p != last) // an exponent part remains
+    {
+        bool exp_negative = false;
+        if (p != last && (*p == '-' || *p == '+'))
+        {
+            exp_negative = (*p == '-');
+            ++p;
+        }
+        bool any_exp_digit = false;
+        for (; p != last; ++p)
+        {
+            if (JSON_HEDLEY_UNLIKELY(*p < '0' || *p > '9'))
+            {
+                return false;
+            }
+            exponent = (exponent * 10) + (*p - '0');
+            any_exp_digit = true;
+            if (JSON_HEDLEY_UNLIKELY(exponent > 9999))
+            {
+                return false;
+            }
+        }
+        if (JSON_HEDLEY_UNLIKELY(!any_exp_digit))
+        {
+            return false;
+        }
+        if (exp_negative)
+        {
+            exponent = -exponent;
+        }
+    }
+
+    const int scale = exponent - fractional_digits;
+    if (JSON_HEDLEY_UNLIKELY(significand >= (static_cast<std::uint64_t>(1) << 53)))
+    {
+        return false; // significand not exactly representable as double
+    }
+
+    auto result = static_cast<double>(significand);
+    if (scale >= 0)
+    {
+        if (JSON_HEDLEY_UNLIKELY(scale > 22))
+        {
+            return false;
+        }
+        result *= powers_of_ten[static_cast<std::size_t>(scale)];
+    }
+    else
+    {
+        if (JSON_HEDLEY_UNLIKELY(-scale > 22))
+        {
+            return false;
+        }
+        result /= powers_of_ten[static_cast<std::size_t>(-scale)];
+    }
+    out = negative ? -result : result;
+    return true;
+#endif
+}
+
+/// fast float path is only exact for `double`; decline for float/long double
+template<typename DecimalPointType, typename FloatType>
+bool parse_float_fast(const char* /*first*/, const char* /*last*/, DecimalPointType /*decimal_point*/, FloatType& /*out*/) noexcept
+{
+    return false;
+}
+
+/*!
+@brief parse a float with std::from_chars (Eisel-Lemire) when available
+
+std::from_chars is locale-independent, correctly rounded, and - via the
+Eisel-Lemire algorithm in modern standard libraries - much faster than strtod
+over the whole value range (not just the Clinger subset). It is used only when
+__cpp_lib_to_chars indicates full floating-point support and only when it
+consumes the entire token ([first, last)); a partial parse means the buffer
+uses a non-'.' locale decimal point, in which case the caller falls back to the
+locale-aware path. An under-/overflow (result_out_of_range) also declines, so
+the caller's strtod fallback supplies the well-defined ±inf/0 result the parser
+expects (side-stepping the P4168 divergence between implementations).
+
+@return true if the value was parsed exactly and fully; false to fall back
+*/
+template<typename FloatType>
+bool parse_float_from_chars(const char* first, const char* last, FloatType& out) noexcept
+{
+    // JSON_HAS_CPP_17 must gate the use as well as the <charconv> include above:
+    // some standard libraries (e.g. libstdc++ 15) define __cpp_lib_to_chars even
+    // in C++14 mode, where <charconv> is not included.
+#if defined(JSON_HAS_CPP_17) && defined(__cpp_lib_to_chars)
+    const auto result = std::from_chars(first, last, out);
+    return result.ec == std::errc() && result.ptr == last;
+#else
+    static_cast<void>(first);
+    static_cast<void>(last);
+    static_cast<void>(out);
+    return false;
+#endif
+}
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/input/string_scan.hpp

@@ -0,0 +1,289 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <cstddef> // size_t
+#include <cstdint> // uint64_t
+#include <cstring> // memcpy
+
+#if defined(JSON_USE_SIMDUTF)
+    // Optional SIMD backend for bulk UTF-8 validation. This is an opt-in
+    // external dependency: nlohmann/json itself stays header-only and the C++11
+    // scalar validator below is always available; defining JSON_USE_SIMDUTF
+    // additionally requires the simdutf headers on the include path and linking
+    // the simdutf library. See string_bulk_run().
+    #include <simdutf.h>
+#endif
+
+#include <nlohmann/detail/macro_scope.hpp>
+
+// This file contains the byte-level string-scanning helpers used by the lexer's
+// contiguous fast path. They operate purely on raw bytes (no dependency on the
+// lexer's template parameters) so they are free functions, keeping the lexer
+// itself focused on the state machine; see lexer::scan_string_bulk().
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+// classify a single byte as needing individual string handling: the closing
+// quote, an escape, a control character, or a non-ASCII (UTF-8)
+// lead/continuation byte. Ordinary bytes (0x20..0x7F except '"' and '\\') are
+// copied verbatim, which the bulk scanner does 8 bytes at a time.
+inline bool is_string_special(unsigned char c) noexcept
+{
+    return c == '\"' || c == '\\' || c < 0x20u || c >= 0x80u;
+}
+
+// SWAR helper: return a word whose high bit is set in every byte of @a v that
+// is_string_special(); zero if the 8 bytes are all ordinary.
+inline std::uint64_t swar_string_special(std::uint64_t v) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'  (0x22)
+    const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\' (0x5C)
+    const std::uint64_t has_quote     = (q - ones) & ~q & high;
+    const std::uint64_t has_backslash = (b - ones) & ~b & high;
+    const std::uint64_t has_control   = (v - 0x2020202020202020ull) & ~v & high; // < 0x20
+    const std::uint64_t has_non_ascii = v & high;                                // >= 0x80
+    return has_quote | has_backslash | has_control | has_non_ascii;
+}
+
+// return the index of the first is_string_special() byte in [data, data+n), or
+// n if every byte is ordinary; scans 8 bytes at a time
+inline std::size_t find_string_special(const unsigned char* data, std::size_t n) noexcept
+{
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        std::uint64_t word = 0;
+        std::memcpy(&word, data + i, sizeof(word));
+        if (swar_string_special(word) != 0)
+        {
+            // a special byte is in this word; locate it (endian-agnostic)
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                if (is_string_special(data[i + j]))
+                {
+                    return i + j;
+                }
+            }
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (is_string_special(data[i]))
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
+// classify a byte as one the serializer must NOT copy verbatim when
+// ensure_ascii is requested: the closing quote, an escape, a control character
+// (< 0x20), DEL (0x7F), or any non-ASCII byte (>= 0x80). Everything else -
+// printable ASCII except '"' and '\\' - is emitted unchanged. Note this differs
+// from is_string_special() only in that 0x7F is also a stop (it is escaped as
+// \u007f under ensure_ascii).
+inline bool is_ascii_copyable(unsigned char c) noexcept
+{
+    return c >= 0x20u && c < 0x7Fu && c != '\"' && c != '\\';
+}
+
+// return the index of the first byte in [data, data+n) that is NOT
+// is_ascii_copyable(), or n if every byte can be copied verbatim; scans 8 bytes
+// at a time. Used by the serializer's ensure_ascii fast path.
+inline std::size_t find_ascii_copyable_run(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        std::uint64_t v = 0;
+        std::memcpy(&v, data + i, sizeof(v));
+        const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'  (0x22)
+        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\' (0x5C)
+        const std::uint64_t d = v ^ 0x7F7F7F7F7F7F7F7Full; // DEL  (0x7F)
+        const std::uint64_t stop = ((q - ones) & ~q & high)   // == '"'
+                                   | ((b - ones) & ~b & high)  // == '\\'
+                                   | ((d - ones) & ~d & high)  // == 0x7F
+                                   | ((v - 0x2020202020202020ull) & ~v & high) // < 0x20
+                                   | (v & high);               // >= 0x80
+        if (stop != 0)
+        {
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                if (!is_ascii_copyable(data[i + j]))
+                {
+                    return i + j;
+                }
+            }
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (!is_ascii_copyable(data[i]))
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
+// Validate one UTF-8 sequence at the front of [data, data+avail). Returns its
+// length (2..4) only when the bytes form a *well-formed* sequence using exactly
+// the same ranges as scan_string()'s per-byte switch, so the bulk path accepts
+// precisely what the byte path accepts. Returns 0 for anything that is invalid,
+// incomplete, or that the byte path must diagnose (the caller then defers to
+// that path, keeping error messages unchanged). Lead bytes < 0x80 are handled
+// by the caller and never passed here.
+inline std::size_t validate_one_utf8(const unsigned char* data, std::size_t avail) noexcept
+{
+    const unsigned char c0 = data[0];
+    if (c0 >= 0xC2 && c0 <= 0xDF)  // U+0080..U+07FF
+    {
+        if (avail >= 2 && data[1] >= 0x80 && data[1] <= 0xBF)
+        {
+            return 2;
+        }
+    }
+    else if (c0 == 0xE0)  // U+0800..U+0FFF
+    {
+        if (avail >= 3 && data[1] >= 0xA0 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF)
+        {
+            return 3;
+        }
+    }
+    else if ((c0 >= 0xE1 && c0 <= 0xEC) || c0 == 0xEE || c0 == 0xEF)  // U+1000..U+CFFF, U+E000..U+FFFF
+    {
+        if (avail >= 3 && data[1] >= 0x80 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF)
+        {
+            return 3;
+        }
+    }
+    else if (c0 == 0xED)  // U+D000..U+D7FF (excludes surrogates)
+    {
+        if (avail >= 3 && data[1] >= 0x80 && data[1] <= 0x9F && data[2] >= 0x80 && data[2] <= 0xBF)
+        {
+            return 3;
+        }
+    }
+    else if (c0 == 0xF0)  // U+10000..U+3FFFF
+    {
+        if (avail >= 4 && data[1] >= 0x90 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF && data[3] >= 0x80 && data[3] <= 0xBF)
+        {
+            return 4;
+        }
+    }
+    else if (c0 >= 0xF1 && c0 <= 0xF3)  // U+40000..U+FFFFF
+    {
+        if (avail >= 4 && data[1] >= 0x80 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF && data[3] >= 0x80 && data[3] <= 0xBF)
+        {
+            return 4;
+        }
+    }
+    else if (c0 == 0xF4)  // U+100000..U+10FFFF
+    {
+        if (avail >= 4 && data[1] >= 0x80 && data[1] <= 0x8F && data[2] >= 0x80 && data[2] <= 0xBF && data[3] >= 0x80 && data[3] <= 0xBF)
+        {
+            return 4;
+        }
+    }
+    return 0; // invalid, incomplete, or must be diagnosed by the byte path
+}
+
+// Scalar (C++11) computation of the bulk run length: the number of leading
+// bytes in [data, data+n) that are ordinary ASCII or complete well-formed UTF-8
+// sequences, stopping before the first byte that needs individual handling (the
+// closing quote, an escape, a control character, or an ill-formed/truncated
+// sequence). ASCII is skipped 8 bytes at a time.
+inline std::size_t scalar_string_bulk_run(const unsigned char* data, std::size_t n) noexcept
+{
+    std::size_t pos = 0;
+    while (pos < n)
+    {
+        pos += find_string_special(data + pos, n - pos);
+        if (pos >= n || data[pos] < 0x80u)
+        {
+            break; // end of buffer, or a quote/escape/control byte
+        }
+        const std::size_t seq = validate_one_utf8(data + pos, n - pos);
+        if (seq == 0)
+        {
+            break; // ill-formed or truncated: let the byte path diagnose it
+        }
+        pos += seq;
+    }
+    return pos;
+}
+
+#if defined(JSON_USE_SIMDUTF)
+// Index of the first quote/escape/control byte in [data, data+n) (non-ASCII
+// bytes are *not* stops here - the whole run is handed to simdutf), or n.
+inline std::size_t find_string_delimiter(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        std::uint64_t v = 0;
+        std::memcpy(&v, data + i, sizeof(v));
+        const std::uint64_t q = v ^ 0x2222222222222222ull;
+        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull;
+        const std::uint64_t hit = ((q - ones) & ~q & high)
+                                  | ((b - ones) & ~b & high)
+                                  | ((v - 0x2020202020202020ull) & ~v & high);
+        if (hit != 0)
+        {
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                const unsigned char c = data[i + j];
+                if (c == '\"' || c == '\\' || c < 0x20u)
+                {
+                    return i + j;
+                }
+            }
+        }
+    }
+    for (; i < n; ++i)
+    {
+        const unsigned char c = data[i];
+        if (c == '\"' || c == '\\' || c < 0x20u)
+        {
+            return i;
+        }
+    }
+    return n;
+}
+#endif
+
+// Backend-dispatched bulk run length. With JSON_USE_SIMDUTF the run up to the
+// next delimiter is validated in one shot by simdutf; on the rare failure the
+// scalar helper recomputes the exact valid prefix so the byte path still
+// produces the precise diagnostic. Without it, the pure scalar path is used.
+inline std::size_t string_bulk_run(const unsigned char* data, std::size_t n) noexcept
+{
+#if defined(JSON_USE_SIMDUTF)
+    const std::size_t run = find_string_delimiter(data, n);
+    if (run != 0 && simdutf::validate_utf8(reinterpret_cast<const char*>(data), run))
+    {
+        return run;
+    }
+    return scalar_string_bulk_run(data, n);
+#else
+    return scalar_string_bulk_run(data, n);
+#endif
+}
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/meta/type_traits.hpp

@@ -231,7 +231,9 @@ struct char_traits<signed char> : std::char_traits<char>
     // Redefine to_int_type function
     static int_type to_int_type(char_type c) noexcept
     {
-        return static_cast<int_type>(c);
+        // cast via unsigned char: sign-extending a negative char_type would make
+        // byte 0xFF indistinguishable from eof()
+        return static_cast<int_type>(static_cast<unsigned char>(c));
     }
 
     static char_type to_char_type(int_type i) noexcept
@@ -699,21 +701,35 @@ struct is_json_pointer_of<A, ::nlohmann::json_pointer<A>> : std::true_type {};
 template <typename A>
 struct is_json_pointer_of<A, ::nlohmann::json_pointer<A>&> : std::true_type {};
 
-// checks if A and B are comparable using Compare functor
+// checks if A and B are comparable using Compare functor, assuming that
+// neither A nor B is a json_pointer type (that case is handled by
+// is_comparable below, which never instantiates this helper otherwise)
 template<typename Compare, typename A, typename B, typename = void>
-struct is_comparable : std::false_type {};
+struct is_comparable_no_json_pointer : std::false_type {};
 
-// We exclude json_pointer here, because the checks using Compare(A, B) will
-// use json_pointer::operator string_t() which triggers a deprecation warning
-// for GCC. See https://github.com/nlohmann/json/issues/4621. The call to
-// is_json_pointer_of can be removed once the deprecated function has been
-// removed.
 template<typename Compare, typename A, typename B>
-struct is_comparable < Compare, A, B, enable_if_t < !is_json_pointer_of<A, B>::value
-&& std::is_constructible <decltype(std::declval<Compare>()(std::declval<A>(), std::declval<B>()))>::value
+struct is_comparable_no_json_pointer < Compare, A, B, enable_if_t <
+std::is_constructible <decltype(std::declval<Compare>()(std::declval<A>(), std::declval<B>()))>::value
 && std::is_constructible <decltype(std::declval<Compare>()(std::declval<B>(), std::declval<A>()))>::value
 >> : std::true_type {};
 
+// checks if A and B are comparable using Compare functor
+// We dispatch on is_json_pointer_of as a plain bool (rather than folding it
+// into a single enable_if_t condition together with the checks below) so
+// that the Compare(A, B) checks are only ever written - and thus only ever
+// instantiated - when A/B are not a json_pointer/string pair. Those checks
+// use json_pointer::operator string_t() (GCC, see #4621) resp. the
+// deprecated json_pointer/string operator== (Clang, see #5288), and merely
+// naming them as later operands of a plain && chain is not sufficient to
+// avoid their instantiation on all compilers, even when the first operand
+// is false. The dispatch on is_json_pointer_of can be removed once the
+// deprecated json_pointer comparison operators have been removed.
+template<typename Compare, typename A, typename B, bool = is_json_pointer_of<A, B>::value>
+struct is_comparable : std::false_type {};
+
+template<typename Compare, typename A, typename B>
+struct is_comparable<Compare, A, B, false> : is_comparable_no_json_pointer<Compare, A, B> {};
+
 template<typename T>
 using detect_is_transparent = typename T::is_transparent;
 

include/nlohmann/detail/output/binary_writer.hpp

@@ -1662,7 +1662,15 @@ class binary_writer
         std::size_t len = (value.at(key).empty() ? 0 : 1);
         for (const auto& el : value.at(key))
         {
-            len *= static_cast<std::size_t>(el.m_data.m_value.number_unsigned);
+            // a dimension is read as an unsigned value below, so anything that
+            // is not a non-negative integer is rejected: a non-integer entry
+            // would pun unrelated bytes as the dimension, and a negative one
+            // would wrap into a nonsensical length
+            if (!el.is_number_integer() || (!el.is_number_unsigned() && el.template get<std::int64_t>() < 0))
+            {
+                return true;
+            }
+            len *= static_cast<std::size_t>(el.template get<std::uint64_t>());
         }
 
         key = "_ArrayData_";
@@ -1671,6 +1679,24 @@ class binary_writer
             return true;
         }
 
+        // every element is written below as the number kind dtype names, so it
+        // has to actually be a number of that category: an element of any other
+        // type would reinterpret unrelated bytes, e.g. a string's heap pointer,
+        // as that number. Such an object falls back to a plain object encoding.
+        // dtype names the wire type, not the storage type: whether an integer
+        // is held as number_integer or number_unsigned depends on how the value
+        // was built (parsing stores non-negative integers as unsigned, the C++
+        // API stores int literals as signed), so both are accepted here and the
+        // writes below go through get<>, which reads the member that is active.
+        const bool ndarray_is_float = (dtype == 'd' || dtype == 'D');
+        for (const auto& el : value.at(key))
+        {
+            if (ndarray_is_float ? !el.is_number_float() : !el.is_number_integer())
+            {
+                return true;
+            }
+        }
+
         oa->write_character('[');
         oa->write_character('$');
         oa->write_character(dtype);
@@ -1684,70 +1710,70 @@ class binary_writer
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::uint8_t>(el.m_data.m_value.number_unsigned), true);
+                write_number(static_cast<std::uint8_t>(el.template get<std::uint64_t>()), true);
             }
         }
         else if (dtype == 'i')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::int8_t>(el.m_data.m_value.number_integer), true);
+                write_number(static_cast<std::int8_t>(el.template get<std::int64_t>()), true);
             }
         }
         else if (dtype == 'u')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::uint16_t>(el.m_data.m_value.number_unsigned), true);
+                write_number(static_cast<std::uint16_t>(el.template get<std::uint64_t>()), true);
             }
         }
         else if (dtype == 'I')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::int16_t>(el.m_data.m_value.number_integer), true);
+                write_number(static_cast<std::int16_t>(el.template get<std::int64_t>()), true);
             }
         }
         else if (dtype == 'm')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::uint32_t>(el.m_data.m_value.number_unsigned), true);
+                write_number(static_cast<std::uint32_t>(el.template get<std::uint64_t>()), true);
             }
         }
         else if (dtype == 'l')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::int32_t>(el.m_data.m_value.number_integer), true);
+                write_number(static_cast<std::int32_t>(el.template get<std::int64_t>()), true);
             }
         }
         else if (dtype == 'M')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::uint64_t>(el.m_data.m_value.number_unsigned), true);
+                write_number(el.template get<std::uint64_t>(), true);
             }
         }
         else if (dtype == 'L')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<std::int64_t>(el.m_data.m_value.number_integer), true);
+                write_number(el.template get<std::int64_t>(), true);
             }
         }
         else if (dtype == 'd')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<float>(el.m_data.m_value.number_float), true);
+                write_number(static_cast<float>(el.template get<double>()), true);
             }
         }
         else if (dtype == 'D')
         {
             for (const auto& el : value.at(key))
             {
-                write_number(static_cast<double>(el.m_data.m_value.number_float), true);
+                write_number(el.template get<double>(), true);
             }
         }
         return false;

include/nlohmann/detail/output/serializer.hpp

@@ -16,6 +16,7 @@
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // uint8_t
 #include <cstdio> // snprintf
+#include <cstring> // memcpy
 #include <limits> // numeric_limits
 #include <string> // string, char_traits
 #include <iomanip> // setfill, setw
@@ -24,6 +25,7 @@
 
 #include <nlohmann/detail/conversions/to_chars.hpp>
 #include <nlohmann/detail/exceptions.hpp>
+#include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/output/binary_writer.hpp>
@@ -109,6 +111,25 @@ class serializer
               const bool ensure_ascii,
               const unsigned int indent_step,
               const unsigned int current_indent = 0)
+    {
+        dump_internal(val, pretty_print, ensure_ascii, indent_step, current_indent);
+        flush();
+    }
+
+  JSON_PRIVATE_UNLESS_TESTED:
+    /*!
+    @brief recursive worker for @ref dump
+
+    Identical in behavior to the historical @ref dump, but writes into the
+    serializer's internal @ref write_buffer instead of issuing a virtual call
+    per token. The public @ref dump wraps this and flushes the buffer once the
+    top-level value has been serialized.
+    */
+    void dump_internal(const BasicJsonType& val,
+                       const bool pretty_print,
+                       const bool ensure_ascii,
+                       const unsigned int indent_step,
+                       const unsigned int current_indent = 0)
     {
         switch (val.m_data.m_type)
         {
@@ -116,13 +137,13 @@ class serializer
             {
                 if (val.m_data.m_value.object->empty())
                 {
-                    o->write_characters("{}", 2);
+                    put_chars("{}", 2);
                     return;
                 }
 
                 if (pretty_print)
                 {
-                    o->write_characters("{\n", 2);
+                    put_chars("{\n", 2);
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
@@ -135,51 +156,51 @@ class serializer
                     auto i = val.m_data.m_value.object->cbegin();
                     for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
                     {
-                        o->write_characters(indent_string.c_str(), new_indent);
-                        o->write_character('\"');
+                        put_chars(indent_string.c_str(), new_indent);
+                        put_char('\"');
                         dump_escaped(i->first, ensure_ascii);
-                        o->write_characters("\": ", 3);
-                        dump(i->second, true, ensure_ascii, indent_step, new_indent);
-                        o->write_characters(",\n", 2);
+                        put_chars("\": ", 3);
+                        dump_internal(i->second, true, ensure_ascii, indent_step, new_indent);
+                        put_chars(",\n", 2);
                     }
 
                     // last element
                     JSON_ASSERT(i != val.m_data.m_value.object->cend());
                     JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
-                    o->write_characters(indent_string.c_str(), new_indent);
-                    o->write_character('\"');
+                    put_chars(indent_string.c_str(), new_indent);
+                    put_char('\"');
                     dump_escaped(i->first, ensure_ascii);
-                    o->write_characters("\": ", 3);
-                    dump(i->second, true, ensure_ascii, indent_step, new_indent);
+                    put_chars("\": ", 3);
+                    dump_internal(i->second, true, ensure_ascii, indent_step, new_indent);
 
-                    o->write_character('\n');
-                    o->write_characters(indent_string.c_str(), current_indent);
-                    o->write_character('}');
+                    put_char('\n');
+                    put_chars(indent_string.c_str(), current_indent);
+                    put_char('}');
                 }
                 else
                 {
-                    o->write_character('{');
+                    put_char('{');
 
                     // first n-1 elements
                     auto i = val.m_data.m_value.object->cbegin();
                     for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
                     {
-                        o->write_character('\"');
+                        put_char('\"');
                         dump_escaped(i->first, ensure_ascii);
-                        o->write_characters("\":", 2);
-                        dump(i->second, false, ensure_ascii, indent_step, current_indent);
-                        o->write_character(',');
+                        put_chars("\":", 2);
+                        dump_internal(i->second, false, ensure_ascii, indent_step, current_indent);
+                        put_char(',');
                     }
 
                     // last element
                     JSON_ASSERT(i != val.m_data.m_value.object->cend());
                     JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
-                    o->write_character('\"');
+                    put_char('\"');
                     dump_escaped(i->first, ensure_ascii);
-                    o->write_characters("\":", 2);
-                    dump(i->second, false, ensure_ascii, indent_step, current_indent);
+                    put_chars("\":", 2);
+                    dump_internal(i->second, false, ensure_ascii, indent_step, current_indent);
 
-                    o->write_character('}');
+                    put_char('}');
                 }
 
                 return;
@@ -189,13 +210,13 @@ class serializer
             {
                 if (val.m_data.m_value.array->empty())
                 {
-                    o->write_characters("[]", 2);
+                    put_chars("[]", 2);
                     return;
                 }
 
                 if (pretty_print)
                 {
-                    o->write_characters("[\n", 2);
+                    put_chars("[\n", 2);
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
@@ -208,37 +229,37 @@ class serializer
                     for (auto i = val.m_data.m_value.array->cbegin();
                             i != val.m_data.m_value.array->cend() - 1; ++i)
                     {
-                        o->write_characters(indent_string.c_str(), new_indent);
-                        dump(*i, true, ensure_ascii, indent_step, new_indent);
-                        o->write_characters(",\n", 2);
+                        put_chars(indent_string.c_str(), new_indent);
+                        dump_internal(*i, true, ensure_ascii, indent_step, new_indent);
+                        put_chars(",\n", 2);
                     }
 
                     // last element
                     JSON_ASSERT(!val.m_data.m_value.array->empty());
-                    o->write_characters(indent_string.c_str(), new_indent);
-                    dump(val.m_data.m_value.array->back(), true, ensure_ascii, indent_step, new_indent);
+                    put_chars(indent_string.c_str(), new_indent);
+                    dump_internal(val.m_data.m_value.array->back(), true, ensure_ascii, indent_step, new_indent);
 
-                    o->write_character('\n');
-                    o->write_characters(indent_string.c_str(), current_indent);
-                    o->write_character(']');
+                    put_char('\n');
+                    put_chars(indent_string.c_str(), current_indent);
+                    put_char(']');
                 }
                 else
                 {
-                    o->write_character('[');
+                    put_char('[');
 
                     // first n-1 elements
                     for (auto i = val.m_data.m_value.array->cbegin();
                             i != val.m_data.m_value.array->cend() - 1; ++i)
                     {
-                        dump(*i, false, ensure_ascii, indent_step, current_indent);
-                        o->write_character(',');
+                        dump_internal(*i, false, ensure_ascii, indent_step, current_indent);
+                        put_char(',');
                     }
 
                     // last element
                     JSON_ASSERT(!val.m_data.m_value.array->empty());
-                    dump(val.m_data.m_value.array->back(), false, ensure_ascii, indent_step, current_indent);
+                    dump_internal(val.m_data.m_value.array->back(), false, ensure_ascii, indent_step, current_indent);
 
-                    o->write_character(']');
+                    put_char(']');
                 }
 
                 return;
@@ -246,9 +267,9 @@ class serializer
 
             case value_t::string:
             {
-                o->write_character('\"');
+                put_char('\"');
                 dump_escaped(*val.m_data.m_value.string, ensure_ascii);
-                o->write_character('\"');
+                put_char('\"');
                 return;
             }
 
@@ -256,7 +277,7 @@ class serializer
             {
                 if (pretty_print)
                 {
-                    o->write_characters("{\n", 2);
+                    put_chars("{\n", 2);
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
@@ -265,9 +286,9 @@ class serializer
                         indent_string.resize(indent_string.size() * 2, ' ');
                     }
 
-                    o->write_characters(indent_string.c_str(), new_indent);
+                    put_chars(indent_string.c_str(), new_indent);
 
-                    o->write_characters("\"bytes\": [", 10);
+                    put_chars("\"bytes\": [", 10);
 
                     if (!val.m_data.m_value.binary->empty())
                     {
@@ -275,30 +296,30 @@ class serializer
                                 i != val.m_data.m_value.binary->cend() - 1; ++i)
                         {
                             dump_integer(*i);
-                            o->write_characters(", ", 2);
+                            put_chars(", ", 2);
                         }
                         dump_integer(val.m_data.m_value.binary->back());
                     }
 
-                    o->write_characters("],\n", 3);
-                    o->write_characters(indent_string.c_str(), new_indent);
+                    put_chars("],\n", 3);
+                    put_chars(indent_string.c_str(), new_indent);
 
-                    o->write_characters("\"subtype\": ", 11);
+                    put_chars("\"subtype\": ", 11);
                     if (val.m_data.m_value.binary->has_subtype())
                     {
                         dump_integer(val.m_data.m_value.binary->subtype());
                     }
                     else
                     {
-                        o->write_characters("null", 4);
+                        put_chars("null", 4);
                     }
-                    o->write_character('\n');
-                    o->write_characters(indent_string.c_str(), current_indent);
-                    o->write_character('}');
+                    put_char('\n');
+                    put_chars(indent_string.c_str(), current_indent);
+                    put_char('}');
                 }
                 else
                 {
-                    o->write_characters("{\"bytes\":[", 10);
+                    put_chars("{\"bytes\":[", 10);
 
                     if (!val.m_data.m_value.binary->empty())
                     {
@@ -306,20 +327,20 @@ class serializer
                                 i != val.m_data.m_value.binary->cend() - 1; ++i)
                         {
                             dump_integer(*i);
-                            o->write_character(',');
+                            put_char(',');
                         }
                         dump_integer(val.m_data.m_value.binary->back());
                     }
 
-                    o->write_characters("],\"subtype\":", 12);
+                    put_chars("],\"subtype\":", 12);
                     if (val.m_data.m_value.binary->has_subtype())
                     {
                         dump_integer(val.m_data.m_value.binary->subtype());
-                        o->write_character('}');
+                        put_char('}');
                     }
                     else
                     {
-                        o->write_characters("null}", 5);
+                        put_chars("null}", 5);
                     }
                 }
                 return;
@@ -329,11 +350,11 @@ class serializer
             {
                 if (val.m_data.m_value.boolean)
                 {
-                    o->write_characters("true", 4);
+                    put_chars("true", 4);
                 }
                 else
                 {
-                    o->write_characters("false", 5);
+                    put_chars("false", 5);
                 }
                 return;
             }
@@ -358,13 +379,13 @@ class serializer
 
             case value_t::discarded:
             {
-                o->write_characters("<discarded>", 11);
+                put_chars("<discarded>", 11);
                 return;
             }
 
             case value_t::null:
             {
-                o->write_characters("null", 4);
+                put_chars("null", 4);
                 return;
             }
 
@@ -400,6 +421,45 @@ class serializer
 
         for (std::size_t i = 0; i < s.size(); ++i)
         {
+            // Fast path: at a character boundary (state == UTF8_ACCEPT),
+            // bulk-copy the longest run of bytes that need no escaping using a
+            // SWAR scanner shared with the lexer's contiguous path. The scanner
+            // stops exactly at the first byte dump_escaped would handle
+            // individually, so that byte is left to the byte-at-a-time path
+            // below, keeping escaping output and error diagnostics unchanged.
+            //
+            // - ensure_ascii == false: string_bulk_run() copies ordinary bytes
+            //   and complete well-formed UTF-8, stopping at a quote, backslash,
+            //   control character (< 0x20), or ill-formed/truncated sequence.
+            // - ensure_ascii == true: only printable ASCII may be copied
+            //   verbatim; find_ascii_copyable_run() additionally stops at 0x7F
+            //   and every non-ASCII byte (>= 0x80), which must be \u-escaped.
+            if (state == UTF8_ACCEPT)
+            {
+                const auto* const data = reinterpret_cast<const unsigned char*>(s.data());
+                const std::size_t run = ensure_ascii
+                                        ? find_ascii_copyable_run(data + i, s.size() - i)
+                                        : string_bulk_run(data + i, s.size() - i);
+                if (run != 0)
+                {
+                    // emit any bytes still pending in string_buffer first to
+                    // preserve output order, then write the run directly
+                    if (bytes != 0)
+                    {
+                        put_chars(string_buffer.data(), bytes);
+                        bytes = 0;
+                    }
+                    put_chars(s.data() + i, run);
+                    bytes_after_last_accept = 0;
+                    undumped_chars = 0;
+                    i += run;
+                    if (i >= s.size())
+                    {
+                        break;
+                    }
+                }
+            }
+
             const auto byte = static_cast<std::uint8_t>(s[i]);
 
             switch (decode(state, codepoint, byte))
@@ -488,7 +548,7 @@ class serializer
                     // written ("\uxxxx\uxxxx\0") for one code point
                     if (string_buffer.size() - bytes < 13)
                     {
-                        o->write_characters(string_buffer.data(), bytes);
+                        put_chars(string_buffer.data(), bytes);
                         bytes = 0;
                     }
 
@@ -547,7 +607,7 @@ class serializer
                                 // written ("\uxxxx\uxxxx\0") for one code point
                                 if (string_buffer.size() - bytes < 13)
                                 {
-                                    o->write_characters(string_buffer.data(), bytes);
+                                    put_chars(string_buffer.data(), bytes);
                                     bytes = 0;
                                 }
 
@@ -586,7 +646,7 @@ class serializer
             // write buffer
             if (bytes > 0)
             {
-                o->write_characters(string_buffer.data(), bytes);
+                put_chars(string_buffer.data(), bytes);
             }
         }
         else
@@ -602,22 +662,22 @@ class serializer
                 case error_handler_t::ignore:
                 {
                     // write all accepted bytes
-                    o->write_characters(string_buffer.data(), bytes_after_last_accept);
+                    put_chars(string_buffer.data(), bytes_after_last_accept);
                     break;
                 }
 
                 case error_handler_t::replace:
                 {
                     // write all accepted bytes
-                    o->write_characters(string_buffer.data(), bytes_after_last_accept);
+                    put_chars(string_buffer.data(), bytes_after_last_accept);
                     // add a replacement character
                     if (ensure_ascii)
                     {
-                        o->write_characters("\\ufffd", 6);
+                        put_chars("\\ufffd", 6);
                     }
                     else
                     {
-                        o->write_characters("\xEF\xBF\xBD", 3);
+                        put_chars("\xEF\xBF\xBD", 3);
                     }
                     break;
                 }
@@ -628,6 +688,66 @@ class serializer
         }
     }
 
+  private:
+    /*!
+    @brief append a single character to the write buffer
+
+    Structural characters ('{', '"', ',', ...) previously went straight to the
+    output adapter, one virtual call each. Buffering them and flushing in bulk
+    turns those many indirect calls into a single memcpy plus an occasional
+    flush, which dominates the cost of serializing object/array-heavy values.
+    */
+    void put_char(char c)
+    {
+        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos == write_buffer.size()))
+        {
+            flush();
+        }
+        write_buffer[write_buffer_pos++] = c;
+    }
+
+    /*!
+    @brief append @a length characters to the write buffer
+
+    Runs that do not fit the buffer are written straight through the output
+    adapter (after flushing what is pending), so large string/number payloads
+    are not copied an extra time.
+    */
+    JSON_HEDLEY_NON_NULL(2)
+    void put_chars(const char* s, std::size_t length)
+    {
+        if (JSON_HEDLEY_UNLIKELY(length >= write_buffer.size()))
+        {
+            flush();
+            o->write_characters(s, length);
+            return;
+        }
+        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos + length > write_buffer.size()))
+        {
+            flush();
+        }
+        std::memcpy(write_buffer.data() + write_buffer_pos, s, length);
+        write_buffer_pos += length;
+    }
+
+  JSON_PRIVATE_UNLESS_TESTED:
+    /*!
+    @brief flush the write buffer to the output adapter
+
+    Writing zero characters is a well-defined no-op for every output adapter, so
+    the buffered length is passed through unconditionally (no empty-guard branch
+    to leave uncovered).
+
+    @note dump_escaped() and dump_integer()/dump_float() write into the internal
+    write buffer; callers that invoke them directly (rather than through the
+    public dump()) must call flush() before inspecting the output.
+    */
+    void flush()
+    {
+        o->write_characters(write_buffer.data(), write_buffer_pos);
+        write_buffer_pos = 0;
+    }
+
   private:
     /*!
     @brief count digits
@@ -752,7 +872,7 @@ class serializer
         // special case for "0"
         if (x == 0)
         {
-            o->write_character('0');
+            put_char('0');
             return;
         }
 
@@ -805,7 +925,7 @@ class serializer
             *(--buffer_ptr) = static_cast<char>('0' + abs_value);
         }
 
-        o->write_characters(number_buffer.data(), n_chars);
+        put_chars(number_buffer.data(), n_chars);
     }
 
     /*!
@@ -821,7 +941,7 @@ class serializer
         // NaN / inf
         if (!std::isfinite(x))
         {
-            o->write_characters("null", 4);
+            put_chars("null", 4);
             return;
         }
 
@@ -842,7 +962,7 @@ class serializer
         auto* begin = number_buffer.data();
         auto* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
 
-        o->write_characters(begin, static_cast<size_t>(end - begin));
+        put_chars(begin, static_cast<size_t>(end - begin));
     }
 
     JSON_HEDLEY_NON_NULL(1)
@@ -893,7 +1013,7 @@ class serializer
             }
         }
 
-        o->write_characters(number_buffer.data(), static_cast<std::size_t>(len));
+        put_chars(number_buffer.data(), static_cast<std::size_t>(len));
 
         // determine if we need to append ".0"
         const bool value_is_int_like =
@@ -905,7 +1025,7 @@ class serializer
 
         if (value_is_int_like)
         {
-            o->write_characters(".0", 2);
+            put_chars(".0", 2);
         }
     }
 
@@ -1015,6 +1135,12 @@ class serializer
 
     /// error_handler how to react on decoding errors
     const error_handler_t error_handler;
+
+    /// buffer collecting output before it is flushed to the output adapter, so
+    /// that the many small structural writes become few bulk writes
+    std::array<char, 1024> write_buffer{{}};
+    /// number of valid bytes currently held in @ref write_buffer
+    std::size_t write_buffer_pos = 0;
 };
 
 }  // namespace detail

tests/src/unit-32bit.cpp

@@ -132,3 +132,37 @@ TEST_CASE("BJData")
         }
     }
 }
+
+TEST_CASE("CBOR")
+{
+    SECTION("parse errors")
+    {
+        SECTION("array/map size larger than std::size_t")
+        {
+            // declared lengths do not fit in a 32-bit std::size_t and must not be truncated
+            std::vector<uint8_t> const varr = {0x9B, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x05};
+            std::vector<uint8_t> const vmap = {0xBB, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x05};
+
+            json _;
+            CHECK_THROWS_WITH_AS(_ = json::from_cbor(varr), "[json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive array size", json::out_of_range&);
+            CHECK(json::from_cbor(varr, true, false).is_discarded());
+
+            CHECK_THROWS_WITH_AS(_ = json::from_cbor(vmap), "[json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive map size", json::out_of_range&);
+            CHECK(json::from_cbor(vmap, true, false).is_discarded());
+        }
+
+        SECTION("array/map size equal to the indefinite-length sentinel")
+        {
+            // on 32-bit platforms a four-byte length of 0xFFFFFFFF aliases unknown_size()
+            std::vector<uint8_t> const varr = {0x9A, 0xFF, 0xFF, 0xFF, 0xFF};
+            std::vector<uint8_t> const vmap = {0xBA, 0xFF, 0xFF, 0xFF, 0xFF};
+
+            json _;
+            CHECK_THROWS_WITH_AS(_ = json::from_cbor(varr), "[json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive array size", json::out_of_range&);
+            CHECK(json::from_cbor(varr, true, false).is_discarded());
+
+            CHECK_THROWS_WITH_AS(_ = json::from_cbor(vmap), "[json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive map size", json::out_of_range&);
+            CHECK(json::from_cbor(vmap, true, false).is_discarded());
+        }
+    }
+}

tests/src/unit-bjdata.cpp

@@ -1347,6 +1347,8 @@ TEST_CASE("BJData")
                     CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vec2), "[json.exception.parse_error.115] parse error at byte 5: syntax error while parsing BJData high-precision number: invalid number text: 1A", json::parse_error);
                     std::vector<uint8_t> const vec3 = {'H', 'i', 2, '1', '.'};
                     CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vec3), "[json.exception.parse_error.115] parse error at byte 5: syntax error while parsing BJData high-precision number: invalid number text: 1.", json::parse_error);
+                    std::vector<uint8_t> const vec_overflow = {'H', 'i', 5, '1', 'e', '4', '0', '0'};
+                    CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vec_overflow), "[json.exception.out_of_range.406] number overflow parsing '1e400'", json::out_of_range);
                     std::vector<uint8_t> const vec4 = {'H', 2, '1', '0'};
                     CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vec4), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing BJData size: expected length type specification (U, i, u, I, m, l, M, L) after '#'; last byte: 0x02", json::parse_error);
                 }
@@ -2587,6 +2589,69 @@ TEST_CASE("BJData")
                 CHECK(json::to_bjdata(json::from_bjdata(v_B), true, true) == v_B);
             }
 
+            SECTION("ndarray with data not matching _ArrayType_ is written as an object")
+            {
+                // A JData-annotated object is only serialized as an ndarray when
+                // its _ArrayData_ elements are actually stored as the number kind
+                // named by _ArrayType_. Otherwise the writer would read the wrong
+                // union member (e.g. a std::string's heap pointer as a uint64) and
+                // emit it, so such an object falls back to a plain object encoding
+                // that still round-trips.
+
+                // string data declared as a uint64 array
+                json const j_str = json({{"_ArrayType_", "uint64"}, {"_ArraySize_", {1}}, {"_ArrayData_", {"pointer"}}});
+                const auto out_str = json::to_bjdata(j_str);
+                CHECK(out_str.at(0) == '{');
+                CHECK(json::from_bjdata(out_str) == j_str);
+
+                // integer data declared as a double array
+                json const j_float = json({{"_ArrayType_", "double"}, {"_ArraySize_", {2}}, {"_ArrayData_", {1, 2}}});
+                const auto out_float = json::to_bjdata(j_float);
+                CHECK(out_float.at(0) == '{');
+                CHECK(json::from_bjdata(out_float) == j_float);
+
+                // a non-integer shape entry is likewise not treated as an ndarray
+                json const j_size = json({{"_ArrayType_", "uint8"}, {"_ArraySize_", {"x"}}, {"_ArrayData_", {1}}});
+                const auto out_size = json::to_bjdata(j_size);
+                CHECK(out_size.at(0) == '{');
+                CHECK(json::from_bjdata(out_size) == j_size);
+
+                // a negative shape entry is not a usable dimension either
+                json const j_neg = json::parse(R"({"_ArrayType_":"uint8","_ArraySize_":[-1],"_ArrayData_":[1]})");
+                const auto out_neg = json::to_bjdata(j_neg);
+                CHECK(out_neg.at(0) == '{');
+                CHECK(json::from_bjdata(out_neg) == j_neg);
+            }
+
+            SECTION("ndarray parsed from text is written as a typed array")
+            {
+                // json::parse stores a non-negative integer as number_unsigned while
+                // the C++ API stores an int literal as number_integer, so _ArrayType_
+                // names the wire type rather than the storage. Both storages have to
+                // produce the same typed array for every type.
+                for (const char* type :
+                        {"uint8", "int8", "uint16", "int16", "uint32", "int32", "uint64", "int64", "char", "byte"
+                        })
+                {
+                    CAPTURE(type);
+                    const std::string text = std::string(R"({"_ArrayType_":")") + type +
+                                             R"(","_ArraySize_":[2,3],"_ArrayData_":[1,2,3,4,5,6]})";
+                    const auto from_text = json::to_bjdata(json::parse(text));
+                    CHECK(from_text.at(0) == '[');
+                    CHECK(from_text == json::to_bjdata(json({{"_ArrayType_", type}, {"_ArraySize_", {2, 3}}, {"_ArrayData_", {1, 2, 3, 4, 5, 6}}})));
+                }
+
+                // negative values under a signed type behave the same way
+                const auto from_neg = json::to_bjdata(json::parse(R"({"_ArrayType_":"int32","_ArraySize_":[2],"_ArrayData_":[-5,7]})"));
+                CHECK(from_neg.at(0) == '[');
+                CHECK(from_neg == json::to_bjdata(json({{"_ArrayType_", "int32"}, {"_ArraySize_", {2}}, {"_ArrayData_", {-5, 7}}})));
+
+                // and so do the floating point types
+                const auto from_float = json::to_bjdata(json::parse(R"({"_ArrayType_":"double","_ArraySize_":[2],"_ArrayData_":[1.5,2.5]})"));
+                CHECK(from_float.at(0) == '[');
+                CHECK(from_float == json::to_bjdata(json({{"_ArrayType_", "double"}, {"_ArraySize_", {2}}, {"_ArrayData_", {1.5, 2.5}}})));
+            }
+
             SECTION("optimized ndarray (type and vector-size as 1D array)")
             {
                 // create vector with two elements of the same type

tests/src/unit-bson.cpp

@@ -529,6 +529,41 @@ TEST_CASE("BSON")
             CHECK(json::from_bson(result, true, false) == j);
         }
 
+        SECTION("non-empty object with binary member without subtype")
+        {
+            const size_t N = 10;
+            const auto s = std::vector<std::uint8_t>(N, 'x');
+            json const j =
+            {
+                { "entry", json::binary(s) }
+            };
+
+            CHECK(!j.at("entry").get_binary().has_subtype());
+
+            std::vector<std::uint8_t> const expected =
+            {
+                0x1B, 0x00, 0x00, 0x00, // size (little endian)
+                0x05, // entry: binary
+                'e', 'n', 't', 'r', 'y', '\x00',
+
+                0x0A, 0x00, 0x00, 0x00, // size of binary (little endian)
+                0x00, // Generic binary subtype
+                0x78, 0x78, 0x78, 0x78, 0x78, 0x78, 0x78, 0x78, 0x78, 0x78,
+
+                0x00 // end marker
+            };
+
+            const auto result = json::to_bson(j);
+            CHECK(result == expected);
+
+            // roundtrip adds the generic binary subtype
+            const auto roundtrip = json::from_bson(result);
+            CHECK(roundtrip != j);
+            CHECK(roundtrip.at("entry").get_binary().has_subtype());
+            CHECK(roundtrip.at("entry").get_binary().subtype() == 0);
+            CHECK(json::from_bson(result, true, false) == roundtrip);
+        }
+
         SECTION("non-empty object with binary member with subtype")
         {
             // an MD5 hash
@@ -825,6 +860,41 @@ TEST_CASE("Incomplete BSON Input")
         CHECK(!json::sax_parse(incomplete_bson, &scp, json::input_format_t::bson));
     }
 
+    SECTION("Incomplete BSON Input 5")
+    {
+        std::vector<std::uint8_t> const incomplete_bson =
+        {
+            0x09, 0x00, 0x00, 0x00, // size (little endian)
+            0x08,                   // entry: boolean
+            'b', '\x00'             // key, unexpected EOF before the value
+        };
+
+        json _;
+        CHECK_THROWS_WITH_AS(_ = json::from_bson(incomplete_bson), "[json.exception.parse_error.110] parse error at byte 8: syntax error while parsing BSON number: unexpected end of input", json::parse_error&);
+        CHECK(json::from_bson(incomplete_bson, true, false).is_discarded());
+
+        SaxCountdown scp(0);
+        CHECK(!json::sax_parse(incomplete_bson, &scp, json::input_format_t::bson));
+    }
+
+    SECTION("Incomplete BSON Input 6")
+    {
+        std::vector<std::uint8_t> const incomplete_bson =
+        {
+            0x0F, 0x00, 0x00, 0x00, // size (little endian)
+            0x05,                   // entry: binary
+            'b', '\x00',            // key
+            0x00, 0x00, 0x00, 0x00  // length, unexpected EOF before the subtype
+        };
+
+        json _;
+        CHECK_THROWS_WITH_AS(_ = json::from_bson(incomplete_bson), "[json.exception.parse_error.110] parse error at byte 12: syntax error while parsing BSON number: unexpected end of input", json::parse_error&);
+        CHECK(json::from_bson(incomplete_bson, true, false).is_discarded());
+
+        SaxCountdown scp(0);
+        CHECK(!json::sax_parse(incomplete_bson, &scp, json::input_format_t::bson));
+    }
+
     SECTION("Improve coverage")
     {
         SECTION("key")

tests/src/unit-cbor.cpp

@@ -1999,6 +1999,42 @@ TEST_CASE("CBOR regressions")
 }
 #endif
 
+TEST_CASE("CBOR definite length equal to the indefinite-length sentinel")
+{
+    // A definite-length array or map whose declared element count equals the
+    // reserved unknown_size() sentinel (SIZE_MAX) must be rejected. Otherwise
+    // it is read as an indefinite-length container and the following bytes are
+    // silently accepted instead of the (impossible) count being reported.
+    json _;
+
+    SECTION("array")
+    {
+        // 0x9B: array with eight-byte length; length = 0xFFFFFFFFFFFFFFFF
+        const std::vector<uint8_t> input = {0x9B, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x01, 0x02, 0xFF};
+        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive array size", json::out_of_range&);
+    }
+
+    SECTION("map")
+    {
+        // 0xBB: map with eight-byte length; length = 0xFFFFFFFFFFFFFFFF
+        const std::vector<uint8_t> input = {0xBB, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x61, 0x61, 0x01, 0xFF};
+        CHECK_THROWS_WITH_AS(_ = json::from_cbor(input), "[json.exception.out_of_range.408] syntax error while parsing CBOR size: excessive map size", json::out_of_range&);
+    }
+
+    SECTION("indefinite-length containers are unaffected")
+    {
+        CHECK(json::from_cbor(std::vector<uint8_t>({0x9F, 0x01, 0x02, 0xFF})) == json({1, 2}));
+        CHECK(json::from_cbor(std::vector<uint8_t>({0xBF, 0x61, 0x61, 0x01, 0xFF})) == json({{"a", 1}}));
+    }
+
+    SECTION("ordinary four-byte length containers are unaffected")
+    {
+        // 0x9A/0xBA carry a four-byte length; a normal count still parses
+        CHECK(json::from_cbor(std::vector<uint8_t>({0x9A, 0x00, 0x00, 0x00, 0x02, 0x01, 0x02})) == json({1, 2}));
+        CHECK(json::from_cbor(std::vector<uint8_t>({0xBA, 0x00, 0x00, 0x00, 0x01, 0x61, 0x61, 0x01})) == json({{"a", 1}}));
+    }
+}
+
 TEST_CASE("CBOR roundtrips" * doctest::skip())
 {
     SECTION("input from flynn")
@@ -2309,7 +2345,7 @@ TEST_CASE("all CBOR first bytes")
 }
 #endif
 
-TEST_CASE("examples from RFC 7049 Appendix A")
+TEST_CASE("examples from RFC 8949 Appendix A")
 {
     SECTION("numbers")
     {

tests/src/unit-class_lexer.cpp

@@ -12,6 +12,10 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#include <sstream> // stringstream
+#include <string> // string
+#include <vector> // vector
+
 namespace
 {
 // shortcut to scan a string literal
@@ -224,3 +228,75 @@ TEST_CASE("lexer class")
         CHECK((scan_string("/**//**//**/", true) == json::lexer::token_type::end_of_input));
     }
 }
+
+TEST_CASE("lexer number fast path")
+{
+    // The contiguous fast path (used for pointer/string input) must agree with
+    // the streaming byte path (used for std::istream) on token type, numeric
+    // value, and round-trip text for every well-formed number, and reject the
+    // same malformed numbers with the same message.
+    SECTION("contiguous vs streaming parity")
+    {
+        const std::vector<std::string> numbers =
+        {
+            "0", "-0", "1", "-1", "42", "-42", "10", "100", "1234567890",
+            "0.0", "-0.0", "3.14", "-3.14", "0.5", "-0.001", "123.456789",
+            "1e0", "1E0", "1e10", "1e-10", "1e+10", "1.5e3", "-2.5E-4",
+            "9223372036854775807",             // INT64_MAX -> unsigned
+            "9223372036854775808",             // INT64_MAX + 1 -> unsigned
+            "18446744073709551615",            // UINT64_MAX -> unsigned
+            "18446744073709551616",            // UINT64_MAX + 1 -> float
+            "-9223372036854775808",            // INT64_MIN -> integer
+            "-9223372036854775809",            // INT64_MIN - 1 -> float
+            "123456789012345678901234567890",  // huge -> float
+            "0.30000000000000004", "2.2250738585072014e-308", "1e308",
+            // high-precision / wide-exponent values that exercise the
+            // std::from_chars (Eisel-Lemire) path beyond the Clinger subset
+            "1.7976931348623157e308", "1.2345678901234567e-250",
+            "9007199254740993", "5e-324", "1e-320"
+        };
+
+        for (const auto& n : numbers)
+        {
+            const std::string doc = "[" + n + "]";
+
+            // contiguous fast path
+            const json a = json::parse(doc);
+            // streaming byte path
+            std::stringstream ss(doc);
+            const json b = json::parse(ss);
+
+            CAPTURE(n);
+            CHECK(a == b);
+            CHECK(a.dump() == b.dump());
+            CHECK(a[0].type() == b[0].type());
+        }
+    }
+
+    SECTION("token type classification")
+    {
+        CHECK((scan_string("0") == json::lexer::token_type::value_unsigned));
+        CHECK((scan_string("-1") == json::lexer::token_type::value_integer));
+        CHECK((scan_string("1.5") == json::lexer::token_type::value_float));
+        CHECK((scan_string("1e5") == json::lexer::token_type::value_float));
+        CHECK((scan_string("18446744073709551615") == json::lexer::token_type::value_unsigned));
+        CHECK((scan_string("18446744073709551616") == json::lexer::token_type::value_float));
+        CHECK((scan_string("-9223372036854775808") == json::lexer::token_type::value_integer));
+        CHECK((scan_string("-9223372036854775809") == json::lexer::token_type::value_float));
+    }
+
+    SECTION("malformed numbers are rejected identically")
+    {
+        for (const char* bad :
+                {"-", "1.", "1e", "1e+", "1.2e", "01", "-01", "1..2", "1.2.3"
+                })
+        {
+            CAPTURE(bad);
+            // the contiguous fast path must decline and let the byte path report
+            const std::string doc = std::string("[") + bad + "]";
+            CHECK_FALSE(json::accept(doc));
+            std::stringstream ss(doc);
+            CHECK_FALSE(json::accept(ss));
+        }
+    }
+}

tests/src/unit-class_parser.cpp

@@ -1440,6 +1440,13 @@ TEST_CASE("parser class")
             ]
         )";
 
+        const auto* structured_object = R"(
+            {
+                "foo": [1, 2],
+                "bar": 3
+            }
+        )";
+
         SECTION("filter nothing")
         {
             const json j_object = json::parse(s_object, [](int /*unused*/, json::parse_event_t /*unused*/, const json& /*unused*/) noexcept
@@ -1515,6 +1522,48 @@ TEST_CASE("parser class")
             CHECK (j_filtered2 == json({1}));
         }
 
+        SECTION("filter array in object")
+        {
+            // the array is discarded once it is already stored under its key
+            const json j_filtered1 = json::parse(structured_object, [](int /*unused*/, json::parse_event_t e, const json& /*parsed*/) noexcept
+            {
+                return e != json::parse_event_t::array_end;
+            });
+
+            CHECK (j_filtered1 == json({{"bar", 3}}));
+
+            // the array is discarded before it is stored, leaving the
+            // placeholder the key event wrote
+            const json j_filtered2 = json::parse(structured_object, [](int /*unused*/, json::parse_event_t e, const json& /*parsed*/) noexcept
+            {
+                return e != json::parse_event_t::array_start;
+            });
+
+            CHECK (j_filtered2 == json({{"bar", 3}}));
+        }
+
+        SECTION("filter value in object")
+        {
+            // the value is discarded after its key was kept, leaving the
+            // placeholder the key event wrote
+            const json j_filtered1 = json::parse(structured_object, [](int /*unused*/, json::parse_event_t e, const json & parsed) noexcept
+            {
+                return !(e == json::parse_event_t::value && parsed == json(3));
+            });
+
+            CHECK (j_filtered1 == json({{"foo", {1, 2}}}));
+
+            // the same value is discarded together with its key, so no
+            // placeholder was stored for it
+            const json j_filtered2 = json::parse(structured_object, [](int /*unused*/, json::parse_event_t e, const json & parsed) noexcept
+            {
+                return !((e == json::parse_event_t::key && parsed == json("bar")) ||
+                         (e == json::parse_event_t::value && parsed == json(3)));
+            });
+
+            CHECK (j_filtered2 == json({{"foo", {1, 2}}}));
+        }
+
         SECTION("filter specific events")
         {
             SECTION("first closing event")

tests/src/unit-convenience.cpp

@@ -100,6 +100,7 @@ void check_escaped(const char* original, const char* escaped, const bool ensure_
     std::stringstream ss;
     json::serializer s(nlohmann::detail::output_adapter<char>(ss), ' ');
     s.dump_escaped(original, ensure_ascii);
+    s.flush(); // dump_escaped writes into the serializer's internal buffer
     CHECK(ss.str() == escaped);
 }
 } // namespace

tests/src/unit-deserialization.cpp

@@ -427,6 +427,30 @@ TEST_CASE("deserialization")
                 CHECK(l.events == std::vector<std::string>({"boolean(true)"}));
             }
 
+            SECTION("from std::vector<signed char>")
+            {
+                std::vector<signed char> const v = {'t', 'r', 'u', 'e'};
+                CHECK(json::parse(v) == json(true));
+                CHECK(json::accept(v));
+
+                SaxEventLogger l;
+                CHECK(json::sax_parse(v, &l));
+                CHECK(l.events.size() == 1);
+                CHECK(l.events == std::vector<std::string>({"boolean(true)"}));
+
+                // bytes outside ASCII are negative here and must not be sign-extended;
+                // 0xC3 and 0xA9 do not fit in signed char (MSVC C4309), so spell them as negative values
+                std::vector<signed char> const umlaut = {'"', static_cast<signed char>(0xC3 - 0x100), static_cast<signed char>(0xA9 - 0x100), '"'};
+                CHECK(json::parse(umlaut) == json("\xC3\xA9"));
+                CHECK(json::accept(umlaut));
+
+                // 0xFF (spelled as -1 to stay in range) must not be reported as end of input
+                std::vector<signed char> const trailing = {'t', 'r', 'u', 'e', static_cast<signed char>(0xFF - 0x100)};
+                json _;
+                CHECK_THROWS_WITH_AS(_ = json::parse(trailing), "[json.exception.parse_error.101] parse error at line 1, column 5: syntax error while parsing value - invalid literal; last read: 'true\xFF'; expected end of input", json::parse_error&);
+                CHECK(!json::accept(trailing));
+            }
+
             SECTION("from std::array")
             {
                 std::array<uint8_t, 5> const v { {'t', 'r', 'u', 'e'} };

tests/src/unit-regression2.cpp

@@ -1530,4 +1530,29 @@ TEST_CASE("issue #4320 - custom base class must not leak nlohmann::detail into A
     CHECK(j == json({{"x", 1.0}, {"y", 2.0}, {"z", 3.0}}));
 }
 
+TEST_CASE("issue #5338 - truncated CBOR tagged binary subtype is rejected")
+{
+    const std::vector<std::vector<std::uint8_t>> truncated_tags =
+    {
+        {0xD8},
+        {0xD9, 0x00},
+        {0xDA, 0x00, 0x00, 0x00},
+        {0xDB, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}
+    };
+
+    for (const auto& data : truncated_tags)
+    {
+        CAPTURE(data);
+        for (const auto tag_handler :
+                {
+                    json::cbor_tag_handler_t::ignore, json::cbor_tag_handler_t::store
+                })
+        {
+            CAPTURE(tag_handler);
+            const auto result = json::from_cbor(data, true, false, tag_handler);
+            CHECK(result.is_discarded());
+        }
+    }
+}
+
 DOCTEST_CLANG_SUPPRESS_WARNING_POP

tests/src/unit-serialization.cpp

@@ -382,3 +382,91 @@ TEST_CASE("dump for basic_json with long double number_float_t")
         check_same(100.0L,  100.0);
     }
 }
+
+TEST_CASE("serialization of strings (bulk fast path)")
+{
+    // These cases exercise the SWAR bulk-copy fast path in dump_escaped and the
+    // internal write buffer: long runs, escapes interrupting runs, 0x7F/DEL,
+    // multibyte UTF-8 under both ensure_ascii settings, and payloads larger than
+    // the write buffer.
+
+    SECTION("long unescaped ASCII exceeds the write buffer")
+    {
+        const std::string big(3000, 'a');
+        const json j = big;
+        CHECK(j.dump() == '"' + big + '"');
+        CHECK(j.dump(-1, ' ', true) == '"' + big + '"');
+        // round-trips
+        CHECK(json::parse(j.dump()) == j);
+    }
+
+    SECTION("runs interrupted by escapes")
+    {
+        const json j = std::string(500, 'x') + "\n\"\\" + std::string(500, 'y');
+        const std::string out = j.dump();
+        CHECK(out == '"' + std::string(500, 'x') + "\\n\\\"\\\\" + std::string(500, 'y') + '"');
+        CHECK(json::parse(out) == j);
+    }
+
+    SECTION("DEL (0x7F) depends on ensure_ascii")
+    {
+        const json j = std::string("a\x7f" "b");
+        CHECK(j.dump(-1, ' ', false) == "\"a\x7f" "b\"");   // copied verbatim
+        CHECK(j.dump(-1, ' ', true) == "\"a\\u007fb\"");    // escaped
+    }
+
+    SECTION("multibyte UTF-8 under both ensure_ascii settings")
+    {
+        const json j = std::string("A\xc3\xa9\xe4\xbd\xa0\xf0\x9f\x98\x80Z"); // A é 你 😀 Z
+        // not escaping non-ASCII: bytes are copied through the bulk validator
+        CHECK(j.dump(-1, ' ', false) == "\"A\xc3\xa9\xe4\xbd\xa0\xf0\x9f\x98\x80Z\"");
+        // ensure_ascii: escaped (with a surrogate pair for the emoji)
+        CHECK(j.dump(-1, ' ', true) == "\"A\\u00e9\\u4f60\\ud83d\\ude00Z\"");
+        CHECK(json::parse(j.dump(-1, ' ', true)) == j);
+    }
+
+    SECTION("many small structural writes exceed the write buffer")
+    {
+        json arr = json::array();
+        for (int i = 0; i < 2000; ++i)
+        {
+            arr.push_back(i);
+        }
+        const std::string out = arr.dump();
+        CHECK(out.front() == '[');
+        CHECK(out.back() == ']');
+        CHECK(json::parse(out) == arr);
+
+        json obj = json::object();
+        for (int i = 0; i < 500; ++i)
+        {
+            obj["key" + std::to_string(i)] = i;
+        }
+        CHECK(json::parse(obj.dump()) == obj);
+        CHECK(json::parse(obj.dump(2)) == obj);
+
+        // an array of many empty strings emits a long run of single-character
+        // writes ('"', '"', ',') at shallow nesting depth, so the write buffer
+        // fills and flushes mid-run without the deep recursion that would
+        // overflow the stack on some debug builds
+        json many_empty = json::array();
+        for (int i = 0; i < 500; ++i)
+        {
+            many_empty.push_back("");
+        }
+        const std::string out2 = many_empty.dump();
+        CHECK(out2.size() > 1024); // spans multiple write-buffer flushes
+        CHECK(out2.front() == '[');
+        CHECK(out2.back() == ']');
+        CHECK(json::parse(out2) == many_empty);
+    }
+
+    SECTION("invalid UTF-8 handling is unaffected by the fast path")
+    {
+        const json j = std::string("valid\xff" "more");
+        CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0xFF", json::type_error&);
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"valid\xef\xbf\xbd" "more\"");
+        CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"valid\\ufffdmore\"");
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"validmore\"");
+    }
+}

tests/src/unit-type_traits.cpp

@@ -53,4 +53,34 @@ TEST_CASE("type traits")
             // NOLINTEND(hicpp-avoid-c-arrays,modernize-avoid-c-arrays,cppcoreguidelines-avoid-c-arrays)
         }
     }
+
+    SECTION("char_traits")
+    {
+        SECTION("to_int_type does not sign-extend")
+        {
+            using unsigned_traits = nlohmann::detail::char_traits<unsigned char>;
+            using signed_traits = nlohmann::detail::char_traits<signed char>;
+
+            CHECK(unsigned_traits::to_int_type(static_cast<unsigned char>(0x7F)) == 0x7F);
+            CHECK(unsigned_traits::to_int_type(static_cast<unsigned char>(0x80)) == 0x80);
+            CHECK(unsigned_traits::to_int_type(static_cast<unsigned char>(0xFF)) == 0xFF);
+
+            CHECK(signed_traits::to_int_type(static_cast<signed char>(0x7F)) == 0x7F);
+            // 0x80 and 0xFF do not fit in signed char (MSVC C4309), so spell them as negative values
+            CHECK(signed_traits::to_int_type(static_cast<signed char>(0x80 - 0x100)) == 0x80);
+            CHECK(signed_traits::to_int_type(static_cast<signed char>(0xFF - 0x100)) == 0xFF);
+        }
+
+        SECTION("no byte value collides with eof")
+        {
+            using unsigned_traits = nlohmann::detail::char_traits<unsigned char>;
+            using signed_traits = nlohmann::detail::char_traits<signed char>;
+
+            for (int i = 0; i < 256; ++i)
+            {
+                CHECK(unsigned_traits::to_int_type(static_cast<unsigned char>(i)) != unsigned_traits::eof());
+                CHECK(signed_traits::to_int_type(static_cast<signed char>(i)) != signed_traits::eof());
+            }
+        }
+    }
 }

tests/src/unit-ubjson.cpp

@@ -819,6 +819,8 @@ TEST_CASE("UBJSON")
                     CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vec2), "[json.exception.parse_error.115] parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1A", json::parse_error);
                     std::vector<uint8_t> const vec3 = {'H', 'i', 2, '1', '.'};
                     CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vec3), "[json.exception.parse_error.115] parse error at byte 5: syntax error while parsing UBJSON high-precision number: invalid number text: 1.", json::parse_error);
+                    std::vector<uint8_t> const vec_overflow = {'H', 'i', 5, '1', 'e', '4', '0', '0'};
+                    CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vec_overflow), "[json.exception.out_of_range.406] number overflow parsing '1e400'", json::out_of_range&);
                     std::vector<uint8_t> const vec4 = {'H', 2, '1', '0'};
                     CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vec4), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing UBJSON size: expected length type specification (U, i, I, l, L) after '#'; last byte: 0x02", json::parse_error);
                 }