Merge branch 'develop' into claude/fix-3669-fa2492

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Use the #3669 fixture's optional member in to_json
2026-09-30 11:40:30 +00:00 · 2026-09-27 20:57:59 +02:00 · 2026-09-27 18:38:52 +02:00 · 2026-09-27 17:07:13 +02:00
21 changed files with 563 additions and 1016 deletions
@@ -80,8 +80,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
  the end of the file was not reached when `strict` was set to true
 - Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from CBOR were
  used in the given input or if the input is not valid CBOR
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of other
-  types are not supported, as JSON object keys are always strings) or a string is malformed
+- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string was expected as a map key,
+  but not found

 ## Complexity

@@ -73,8 +73,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
  the end of the file was not reached when `strict` was set to true
 - Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from
  MessagePack were used in the given input or if the input is not valid MessagePack
- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of other
-  types are not supported, as JSON object keys are always strings) or a string is malformed
+- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string was expected as a map key,
+  but not found

 ## Complexity

@@ -79,6 +79,7 @@ Some important things:
 * When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). (There is a way to bypass this requirement described later.)
 * In function `from_json`, use function [`at()`](../api/basic_json/at.md) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
 * You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
+* If you control the type, consider defining `to_json`/`from_json` as `friend` functions inside the class ("hidden friends"). Argument-dependent lookup then only finds them for your type, which also avoids a [GCC < 11 compilation error](../home/faq.md#incomplete-detector-type-with-gcc-11).


 ## Simplify your life with macros
@@ -174,20 +174,7 @@ The library maps CBOR types to JSON value types as follows:

 !!! warning "Object keys"

-    CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps
-    with keys other than text strings (major type 3) are rejected with a
-    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with `allow_exceptions` set
-    to `false`, a discarded value) naming the type of the key that was found, for instance:
-
-    ```
-    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR object key: only string keys are supported, but found an unsigned integer; last byte: 0x01
-    ```
-
-    This applies to the [SAX interface](../parsing/sax_interface.md) as well, as the key is read before it is passed
-    on. This is a deliberate restriction of the library's JSON value model, not an oversight: formats built on CBOR
-    maps with integer keys, such as COSE ([RFC 9052](https://www.rfc-editor.org/rfc/rfc9052.html)) or CWT
-    ([RFC 8392](https://www.rfc-editor.org/rfc/rfc8392.html)), cannot be read with this library and need a
-    general-purpose CBOR library instead.
+    CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected.

 !!! warning "UTF-8 validation of text strings"

@@ -138,21 +138,6 @@ The library maps MessagePack types to JSON value types as follows:

    Any MessagePack output created by `to_msgpack` can be successfully parsed by `from_msgpack`.

-!!! warning "Object keys"
-
-    MessagePack allows map keys of any type, whereas JSON only allows strings as keys in object values. Like the
-    JSON-compatible [profile](https://github.com/msgpack/msgpack/blob/master/spec.md#profile) sketched in the
-    MessagePack specification, this library restricts map keys to `str` values. Maps with keys of any other type are
-    rejected with a [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with
-    `allow_exceptions` set to `false`, a discarded value) naming the type of the key that was found, for instance:
-
-    ```
-    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack object key: only string keys are supported, but found nil; last byte: 0xC0
-    ```
-
-    This applies to the [SAX interface](../parsing/sax_interface.md) as well, as the key is read before it is passed
-    on. Such input needs a general-purpose MessagePack library instead.
-
 !!! warning "UTF-8 validation of string values"

    The MessagePack specification requires `str` values (`fixstr`, `str 8`, `str 16`, `str 32`) to be valid UTF-8.
@@ -343,20 +343,13 @@ A string could not be read from a [binary format](../features/binary_formats/ind
 string was read where one was required (for instance as a map key), the string's length specification is invalid, or
 the string's bytes are not valid UTF-8.

-CBOR and MessagePack allow map keys of any type, but JSON object keys are always strings. Maps with keys of any other
-type (for instance integers or `null`) are therefore not supported; see the notes on
-[CBOR](../features/binary_formats/cbor.md) and [MessagePack](../features/binary_formats/messagepack.md).
-
 !!! failure "Example messages"

    ```
-    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR object key: only string keys are supported, but found an unsigned integer; last byte: 0x01
+    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xFF
    ```
    ```
-    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack object key: only string keys are supported, but found nil; last byte: 0xC0
-    ```
-    ```
-    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x7C
+    [json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack string: expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0xFF
    ```
    ```
    [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
@@ -307,6 +307,51 @@ APP_CPPFLAGS += -frtti -fexceptions
 The code compiles successfully with [Android NDK](https://developer.android.com/ndk/index.html?hl=ml), Revision 9 - 11 (and possibly later) and [CrystaX's Android NDK](https://www.crystax.net/en/android/ndk) version 10.


+### Incomplete `detector` type with GCC < 11
+
+!!! question
+
+    Why does GCC 10 or older fail with `invalid use of incomplete type 'struct nlohmann::detail::detector<..., to_json_function, ...>'` for a type that holds an `optional` member?
+
+This happens with GCC 10 and older in C++11/C++14 mode when all of these hold:
+
+- a class `Holder` has an `optional<Dummy>` member (e.g., `boost::optional`),
+- `Dummy` has a constructor taking a `json` value, and
+- `to_json` for `Holder` is a free function in the namespace of `Dummy`.
+
+```cpp
+class Dummy {
+  public:
+    explicit Dummy(const nlohmann::json& j);
+};
+
+class Holder {
+    boost::optional<Dummy> d;
+};
+
+void to_json(nlohmann::json& j, const Holder& h);  // triggers the error
+```
+
+To decide whether `Dummy` is copyable, the compiler checks whether a `Dummy` can be converted to `json`. That check
+looks up `to_json` via argument-dependent lookup, finds the unrelated `to_json` for `Holder`, and eventually asks again
+whether `Dummy` is copyable. GCC before version 11 turns this cycle into a hard error; GCC 11 and later, Clang, and
+C++17 mode compile the code. The same error shows up without this library whenever a constrained converting constructor
+is involved, so the library can't avoid it.
+
+To work around this, define `to_json` (and `from_json`) as a *hidden friend* inside the class. That way,
+argument-dependent lookup only finds it for `Holder`:
+
+```cpp
+class Holder {
+    boost::optional<Dummy> d;
+
+    friend void to_json(nlohmann::json& j, const Holder& h) { /* ... */ }
+};
+```
+
+The [`NLOHMANN_DEFINE_TYPE_INTRUSIVE`](../api/macros/nlohmann_define_type_intrusive.md) macros define hidden friends as
+well. See [#3669](https://github.com/nlohmann/json/issues/3669) for details.
+
 ### Missing STL function

 !!! question "Questions"
@@ -1324,80 +1324,6 @@ class binary_reader
        }
    }

-    /*!
-    @brief reads a CBOR object key
-
-    RFC 8949 allows any data item as a map key, but only strings have a
-    counterpart in JSON. A key of any other type is rejected with a message
-    naming that type, rather than the one @ref get_cbor_string gives for a
-    malformed string.
-
-    @param[out] result  created key
-
-    @return whether key creation completed
-    */
-    bool get_cbor_object_key(string_t& result)
-    {
-        // EOF and major type 3 (text string) are left to get_cbor_string
-        if (current == char_traits<char_type>::eof() || (static_cast<unsigned int>(current) & 0xE0u) == 0x60u)
-        {
-            return get_cbor_string(result);
-        }
-
-        const char* found = nullptr;
-        switch (static_cast<unsigned int>(current) >> 5u)
-        {
-            case 0:
-                found = "an unsigned integer";
-                break;
-            case 1:
-                found = "a negative integer";
-                break;
-            case 2:
-                found = "a byte string";
-                break;
-            case 4:
-                found = "an array";
-                break;
-            case 5:
-                found = "a map";
-                break;
-            case 6:
-                found = "a tag";
-                break;
-            default: // major type 7
-                switch (current)
-                {
-                    case 0xF4:
-                    case 0xF5:
-                        found = "a boolean";
-                        break;
-                    case 0xF6:
-                        found = "null";
-                        break;
-                    case 0xF7:
-                        found = "undefined";
-                        break;
-                    case 0xF9:
-                    case 0xFA:
-                    case 0xFB:
-                        found = "a floating-point number";
-                        break;
-                    case 0xFF:
-                        found = "a break stop code";
-                        break;
-                    default:
-                        found = "a simple value";
-                        break;
-                }
-                break;
-        }
-
-        auto last_token = get_token_string();
-        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
-                                exception_message(input_format_t::cbor, concat("only string keys are supported, but found ", found, "; last byte: 0x", last_token), "object key"), nullptr));
-    }
-
    /*!
    @brief reads a definite-length CBOR byte array

@@ -1642,7 +1568,7 @@ class binary_reader
                if (top.is_object)
                {
                    key.clear();
-                    if (JSON_HEDLEY_UNLIKELY(!get_cbor_object_key(key) || !sax->key(key)))
+                    if (JSON_HEDLEY_UNLIKELY(!get_cbor_string(key) || !sax->key(key)))
                    {
                        return false;
                    }
@@ -2143,98 +2069,6 @@ class binary_reader
        }
    }

-    /*!
-    @brief reads a MessagePack object key
-
-    The MessagePack specification allows any type as a map key, but only
-    strings have a counterpart in JSON. A key of any other type is rejected
-    with a message naming that type, rather than the one @ref
-    get_msgpack_string gives for a malformed string.
-
-    @param[out] result  created key
-
-    @return whether key creation completed
-    */
-    bool get_msgpack_object_key(string_t& result)
-    {
-        const char* found = nullptr;
-        switch (current)
-        {
-            case 0xC0:
-                found = "nil";
-                break;
-            case 0xC2:
-            case 0xC3:
-                found = "a boolean";
-                break;
-            case 0xCA:
-            case 0xCB:
-                found = "a float";
-                break;
-            case 0xC4:
-            case 0xC5:
-            case 0xC6:
-                found = "a bin";
-                break;
-            case 0xC7:
-            case 0xC8:
-            case 0xC9:
-            case 0xD4:
-            case 0xD5:
-            case 0xD6:
-            case 0xD7:
-            case 0xD8:
-                found = "an ext";
-                break;
-            case 0xCC:
-            case 0xCD:
-            case 0xCE:
-            case 0xCF:
-            case 0xD0:
-            case 0xD1:
-            case 0xD2:
-            case 0xD3:
-                found = "an integer";
-                break;
-            case 0xDC:
-            case 0xDD:
-                found = "an array";
-                break;
-            case 0xDE:
-            case 0xDF:
-                found = "a map";
-                break;
-            default:
-                // fixint, fixmap, and fixarray; strings, EOF, and the unused
-                // byte 0xC1 are left to get_msgpack_string
-                if (current == char_traits<char_type>::eof())
-                {
-                    return get_msgpack_string(result);
-                }
-                if (current <= 0x7F || current >= 0xE0)
-                {
-                    found = "an integer";
-                }
-                else if (current <= 0x8F)
-                {
-                    found = "a map";
-                }
-                else if (current <= 0x9F)
-                {
-                    found = "an array";
-                }
-                else
-                {
-                    return get_msgpack_string(result);
-                }
-                break;
-        }
-
-        auto last_token = get_token_string();
-        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
-                                exception_message(input_format_t::msgpack, concat("only string keys are supported, but found ", found, "; last byte: 0x", last_token), "object key"), nullptr));
-    }
-
    /*!
    @brief reads a MessagePack byte array

@@ -2397,7 +2231,7 @@ class binary_reader
                {
                    get();
                    key.clear();
-                    if (JSON_HEDLEY_UNLIKELY(!get_msgpack_object_key(key) || !sax->key(key)))
+                    if (JSON_HEDLEY_UNLIKELY(!get_msgpack_string(key) || !sax->key(key)))
                    {
                        return false;
                    }
@@ -206,6 +206,7 @@ class lexer : public lexer_base<BasicJsonType>
    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false, bool discard_number_values_ = false) noexcept
        : ia(std::move(adapter))
        , ignore_comments(ignore_comments_)
+        , decimal_point_char(static_cast<char_int_type>(get_decimal_point()))
        , discard_number_values(discard_number_values_)
    {}

@@ -221,7 +222,8 @@ class lexer : public lexer_base<BasicJsonType>
    // locales
    /////////////////////

-    /// return the decimal point of the current locale
+    /// return the locale-dependent decimal point
+    JSON_HEDLEY_PURE
    static char get_decimal_point() noexcept
    {
        const auto* loc = localeconv();
@@ -1090,10 +1092,9 @@ class lexer : public lexer_base<BasicJsonType>
            token_type::value_float if number could be successfully scanned,
            token_type::parse_error otherwise

-    @note The scanner is independent of the current locale: token_buffer
-          always holds `.`. Only the std::strtod fallback of convert_number()
-          depends on the locale, and it looks up the decimal point right
-          before converting (see convert_float_locale_aware()).
+    @note The scanner is independent of the current locale. Internally, the
+          locale's decimal point is used instead of `.` to work with the
+          locale-dependent converters.
    */
    token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
    {
@@ -1182,7 +1183,7 @@ scan_number_zero:
        {
            case '.':
            {
-                add(current);
+                add(decimal_point_char);
                decimal_point_position = token_buffer.size() - 1;
                goto scan_number_decimal1;
            }
@@ -1219,7 +1220,7 @@ scan_number_any1:

            case '.':
            {
-                add(current);
+                add(decimal_point_char);
                decimal_point_position = token_buffer.size() - 1;
                goto scan_number_decimal1;
            }
@@ -1461,9 +1462,9 @@ scan_number_done:

        // Only a number below 1 can carry further insignificant zeros, and only
        // while the count stays at the limit does removing them change the
-        // answer - so this loop is skipped for all but a few tokens. The
-        // fraction is located through decimal_point_position rather than by
-        // searching '.'.
+        // answer - so this loop is skipped for all but a few tokens. Note
+        // token_buffer holds the locale's decimal point, so the fraction is
+        // located through decimal_point_position rather than by searching '.'.
        if (lead_zero != 0)
        {
            JSON_ASSERT(has_dot != 0); // an integer "0" cannot reach the limit
@@ -1481,8 +1482,8 @@ scan_number_done:
    @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 '.'
-    as decimal point, independent of the locale. Integers are parsed first and fall
+    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.

@@ -1562,7 +1563,7 @@ scan_number_done:
        // 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/strtold.
+        // locale-aware strtof/strtod.
        if (parse_float_from_chars(num_begin, num_end, value_float))
        {
            return token_type::value_float;
@@ -1571,75 +1572,26 @@ scan_number_done:
        // extra pass over the token's bytes, which otherwise shows up on
        // high-precision inputs such as canada.json
        if (mantissa_fits_clinger(mantissa_end)
-                && parse_float_fast(num_begin, num_end, value_float))
+                && parse_float_fast(num_begin, num_end, decimal_point_char, value_float))
        {
            return token_type::value_float;
        }

-        convert_float_locale_aware();
+        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
+        JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
+
        return token_type::value_float;
    }

-    /*!
-    @brief convert the float in token_buffer with strtof/strtod/strtold
-
-    These functions expect the decimal point of the *current* locale, so it is
-    looked up right before the conversion instead of once when the lexer is
-    constructed: a locale change in between (by a parser callback, a SAX
-    handler, or another thread) must not truncate the value (#5198). The
-    token has been validated before, so if the conversion stops early and the
-    decimal point changed in the meantime, the locale changed between the
-    lookup and the call, and the conversion is repeated with the new decimal
-    point. If the decimal point did not change, a retry cannot succeed: the
-    locale's decimal point is not a single character (e.g., the two-byte
-    U+066B of ar_EG.UTF-8 or fa_IR.UTF-8) and cannot be substituted in place.
-    The value strtod parsed up to that point is kept, as before this change.
-
-    Note that changing the locale in another thread *while* strtod runs is
-    undefined behavior of the C library, which this function cannot prevent.
-    */
-    void convert_float_locale_aware()
-    {
-        const bool has_dot = decimal_point_position != std::string::npos;
-        char decimal_point = get_decimal_point();
-        for (;;)
-        {
-            const bool substitute = has_dot && decimal_point != '.';
-            if (substitute)
-            {
-                token_buffer[decimal_point_position] = static_cast<typename string_t::value_type>(decimal_point);
-            }
-
-            char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-            strtof(value_float, token_buffer.data(), &endptr);
-
-            if (substitute)
-            {
-                // get_string() hands the token to the SAX interface with '.'
-                token_buffer[decimal_point_position] = '.';
-            }
-
-            if (JSON_HEDLEY_LIKELY(endptr == token_buffer.data() + token_buffer.size()))
-            {
-                return;
-            }
-
-            // retry only if the locale changed; otherwise, this would loop forever
-            const char current_decimal_point = get_decimal_point();
-            if (current_decimal_point == decimal_point)
-            {
-                return;
-            }
-            decimal_point = current_decimal_point;
-        }
-    }
-
    /*!
    @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
-    (as scan_number() does) and
+    (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
@@ -1755,11 +1707,16 @@ scan_number_done:
        }
 #endif

-        // materialize the token exactly as scan_number() would. reset() already
-        // cleared token_buffer, so append() fills it (assign() is avoided
-        // because custom string_t types need not provide it)
+        // 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)
        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), len);
-        decimal_point_position = dot_index;
+        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;
+        }

        ia.bulk_skip(len - 1);
        position.chars_read_total += (len - 1);
@@ -2026,7 +1983,11 @@ scan_number_done:
    /// return current string value (implicitly resets the token; useful only once)
    string_t& get_string()
    {
-        // a number token holds '.' regardless of the locale (#4084)
+        // translate decimal points from locale back to '.' (#4084)
+        if (decimal_point_char != '.' && decimal_point_position != std::string::npos)
+        {
+            token_buffer[decimal_point_position] = '.';
+        }
        return token_buffer;
    }

@@ -2322,7 +2283,9 @@ scan_number_done:
    number_unsigned_t value_unsigned = 0;
    number_float_t value_float = 0;

-    /// the position of the decimal point in token_buffer
+    /// the decimal point
+    const char_int_type decimal_point_char = '.';
+    /// the position of the decimal point in the input
    std::size_t decimal_point_position = std::string::npos;

    /// whether the caller (e.g. accept()/json_sax_acceptor) only needs the
@@ -118,12 +118,14 @@ 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[out] out    the parsed value on success
+@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
 */
-inline bool parse_float_fast(const char* first, const char* last, double& out) noexcept
+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
@@ -134,6 +136,7 @@ inline bool parse_float_fast(const char* first, const char* last, double& out) n
    // 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
@@ -172,7 +175,7 @@ inline bool parse_float_fast(const char* first, const char* last, double& out) n
            ++num_digits;
            fractional_digits += static_cast<int>(seen_dot);
        }
-        else if (c == '.')
+        else if (static_cast<DecimalPointType>(c) == decimal_point)
        {
            if (JSON_HEDLEY_UNLIKELY(seen_dot))
            {
@@ -257,8 +260,8 @@ inline bool parse_float_fast(const char* first, const char* last, double& out) n
 }

 /// fast float path is only exact for `double`; decline for float/long double
-template<typename FloatType>
-bool parse_float_fast(const char* /*first*/, const char* /*last*/, FloatType& /*out*/) noexcept
+template<typename DecimalPointType, typename FloatType>
+bool parse_float_fast(const char* /*first*/, const char* /*last*/, DecimalPointType /*decimal_point*/, FloatType& /*out*/) noexcept
 {
    return false;
 }
@@ -270,7 +273,9 @@ 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)). An under-/overflow (result_out_of_range) also declines, so
+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).

@@ -29,7 +29,6 @@
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/output/output_adapters.hpp>
 #include <nlohmann/detail/string_concat.hpp>
-#include <nlohmann/detail/string_utils.hpp>

 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -2279,10 +2278,20 @@ class binary_writer
        const std::size_t valid = valid_utf8_prefix(data, s.size());
        if (JSON_HEDLEY_UNLIKELY(valid != s.size()))
        {
-            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(valid), ": 0x", detail::hex_byte(data[valid])), &context));
+            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(valid), ": 0x", hex_byte(data[valid])), &context));
        }
    }

+    /// @return a byte as two uppercase hexadecimal digits
+    static std::string hex_byte(const std::uint8_t byte)
+    {
+        std::string result = "00";
+        constexpr const char* nibble_to_hex = "0123456789ABCDEF";
+        result[0] = nibble_to_hex[byte / 16];
+        result[1] = nibble_to_hex[byte % 16];
+        return result;
+    }
+
    /*!
    @brief write an integer in the shortest encoding

@@ -8,7 +8,9 @@

 #pragma once

+#include <algorithm> // copy
 #include <cstddef> // size_t
+#include <iterator> // back_inserter
 #include <memory> // shared_ptr, make_shared
 #include <string> // basic_string
 #include <utility> // move
@@ -29,10 +31,6 @@ namespace detail
 template<typename CharType> struct output_adapter_protocol
 {
    virtual void write_character(CharType c) = 0;
-    /// @param[in] s      pointer to the characters to write; binary_writer legitimately
-    ///                   passes a null pointer together with length 0 for an empty
-    ///                   string or binary value, so implementations must tolerate that
-    /// @param[in] length number of characters at @a s
    virtual void write_characters(const CharType* s, std::size_t length) = 0;
    virtual ~output_adapter_protocol() = default;

@@ -99,6 +97,7 @@ class output_vector_adapter : public output_adapter_protocol<CharType>
        sink.write_character(c);
    }

+    JSON_HEDLEY_NON_NULL(2)
    void write_characters(const CharType* s, std::size_t length) override
    {
        sink.write_characters(s, length);
@@ -123,6 +122,7 @@ class output_stream_adapter : public output_adapter_protocol<CharType>
        stream.put(c);
    }

+    JSON_HEDLEY_NON_NULL(2)
    void write_characters(const CharType* s, std::size_t length) override
    {
        stream.write(s, static_cast<std::streamsize>(length));
@@ -147,6 +147,7 @@ class output_string_adapter : public output_adapter_protocol<CharType>
        str.push_back(c);
    }

+    JSON_HEDLEY_NON_NULL(2)
    void write_characters(const CharType* s, std::size_t length) override
    {
        str.append(s, length);
@@ -3,23 +3,24 @@
 // |  |  |__   |  |  | | | |  version 3.12.0
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
+// SPDX-FileCopyrightText: 2008, 2009 Björn Hoehrmann <bjoern@hoehrmann.de>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT

 #pragma once

-#include <algorithm> // remove, fill, find, none_of, min
+#include <algorithm> // reverse, remove, fill, find, none_of, min
 #include <array> // array
 #include <clocale> // localeconv, lconv
-#include <cmath> // isfinite
+#include <cmath> // labs, isfinite, isnan, signbit
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // uint8_t
 #include <cstdio> // snprintf
 #include <cstring> // memcpy, memset
-#include <iterator> // next
 #include <limits> // numeric_limits
 #include <string> // string, char_traits
 #include <type_traits> // is_same
+#include <utility> // move
 #include <vector> // vector

 #include <nlohmann/detail/conversions/to_chars.hpp>
@@ -27,6 +28,7 @@
 #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>
 #include <nlohmann/detail/output/output_adapters.hpp>
 #include <nlohmann/detail/recursion_depth_limit.hpp>
 #include <nlohmann/detail/string_concat.hpp>
@@ -104,10 +106,9 @@ class serializer
    additional parameter. Arrays and objects are serialized without recursion,
    however deeply they are nested.

-    - strings and object keys are escaped using @ref dump_escaped
-    - integer numbers are converted using a digit-pair lookup table (@ref dump_integer)
-    - floating-point numbers are converted to a string using @ref dump_float, which
-      uses `to_chars` for IEEE-754 types and `snprintf` otherwise
+    - strings and object keys are escaped using `escape_string()`
+    - integer numbers are converted implicitly via `operator<<`
+    - floating-point numbers are converted to a string using `"%g"` format
    - binary values are serialized as objects containing the subtype and the
      byte array

@@ -282,16 +283,127 @@ class serializer
            }

            case value_t::string:
-            case value_t::binary:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::discarded:
-            case value_t::null:
-            default:
-                dump_scalar(val, current_indent);
+            {
+                put_char('"');
+                dump_escaped(*val.m_data.m_value.string);
+                put_char('"');
                return;
+            }
+
+            case value_t::binary:
+            {
+                if (pretty_print)
+                {
+                    put_literal("{\n");
+
+                    // variable to hold indentation for recursive calls
+                    const auto new_indent = next_indent(current_indent, indent_step);
+
+                    put_indent(new_indent);
+
+                    put_literal("\"bytes\": [");
+
+                    if (!val.m_data.m_value.binary->empty())
+                    {
+                        for (auto i = val.m_data.m_value.binary->cbegin();
+                                i != val.m_data.m_value.binary->cend() - 1; ++i)
+                        {
+                            dump_byte(*i);
+                            put_literal(", ");
+                        }
+                        dump_byte(val.m_data.m_value.binary->back());
+                    }
+
+                    put_literal("],\n");
+                    put_indent(new_indent);
+
+                    put_literal("\"subtype\": ");
+                    if (val.m_data.m_value.binary->has_subtype())
+                    {
+                        dump_integer(val.m_data.m_value.binary->subtype());
+                    }
+                    else
+                    {
+                        put_literal("null");
+                    }
+                    put_char('\n');
+                    put_indent(current_indent);
+                    put_char('}');
+                }
+                else
+                {
+                    put_literal("{\"bytes\":[");
+
+                    if (!val.m_data.m_value.binary->empty())
+                    {
+                        for (auto i = val.m_data.m_value.binary->cbegin();
+                                i != val.m_data.m_value.binary->cend() - 1; ++i)
+                        {
+                            dump_byte(*i);
+                            put_char(',');
+                        }
+                        dump_byte(val.m_data.m_value.binary->back());
+                    }
+
+                    put_literal("],\"subtype\":");
+                    if (val.m_data.m_value.binary->has_subtype())
+                    {
+                        dump_integer(val.m_data.m_value.binary->subtype());
+                        put_char('}');
+                    }
+                    else
+                    {
+                        put_literal("null}");
+                    }
+                }
+                return;
+            }
+
+            case value_t::boolean:
+            {
+                if (val.m_data.m_value.boolean)
+                {
+                    put_literal("true");
+                }
+                else
+                {
+                    put_literal("false");
+                }
+                return;
+            }
+
+            case value_t::number_integer:
+            {
+                dump_integer(val.m_data.m_value.number_integer);
+                return;
+            }
+
+            case value_t::number_unsigned:
+            {
+                dump_integer(val.m_data.m_value.number_unsigned);
+                return;
+            }
+
+            case value_t::number_float:
+            {
+                dump_float(val.m_data.m_value.number_float);
+                return;
+            }
+
+            case value_t::discarded:
+            {
+                put_literal("<discarded>");
+                return;
+            }
+
+            case value_t::null:
+            {
+                put_literal("null");
+                return;
+            }
+
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
        }
    }

@@ -448,9 +560,9 @@ class serializer
    @brief serialize the value @a val, but not the elements of a container

    An object or array with elements is opened and pushed onto @a stack for
-    @ref dump_iteratively to walk; everything else - including a binary value,
+    @ref dump_internal to walk; everything else - including a binary value,
    which looks like an object but has no elements to descend into - is written
-    out in full by @ref dump_scalar.
+    out here in full.
    */
    void dump_value(const BasicJsonType& val,
                    const std::size_t current_indent,
@@ -508,35 +620,6 @@ class serializer
                return;
            }

-            case value_t::string:
-            case value_t::binary:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::discarded:
-            case value_t::null:
-            default:
-                dump_scalar(val, current_indent);
-                return;
-        }
-    }
-
-    /*!
-    @brief serialize the value @a val, which is neither an object nor an array
-
-    Shared by @ref dump_internal and @ref dump_value, so that a value is written
-    the same way however deeply it is nested. A binary value is written out here
-    in full: it looks like an object, but has no elements to descend into.
-
-    @param[in] val             value to serialize; not an object or array
-    @param[in] current_indent  the indentation of @a val, used for a
-                               pretty-printed binary value
-    */
-    void dump_scalar(const BasicJsonType& val, const std::size_t current_indent)
-    {
-        switch (val.m_data.m_type)
-        {
            case value_t::string:
            {
                put_char('"');
@@ -657,8 +740,6 @@ class serializer
                return;
            }

-            case value_t::object: // LCOV_EXCL_LINE
-            case value_t::array:  // LCOV_EXCL_LINE
            default:            // LCOV_EXCL_LINE
                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
        }
@@ -687,7 +768,7 @@ class serializer
    Escape a string by replacing certain special characters by a sequence of an
    escape character (backslash) and another character and other control
    characters by a sequence of "\u" followed by a four-digit hex
-    representation. The escaped string is appended to @ref write_buffer.
+    representation. The escaped string is written to output stream @a o.

    @param[in] s  the string to escape

@@ -881,7 +962,7 @@ class serializer
                    {
                        case error_handler_t::strict:
                        {
-                            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", detail::hex_byte(byte)), nullptr));
+                            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", hex_bytes(byte | 0)), nullptr));
                        }

                        case error_handler_t::ignore:
@@ -914,9 +995,9 @@ class serializer
                                }
                                else
                                {
-                                    string_buffer[bytes++] = '\xEF';
-                                    string_buffer[bytes++] = '\xBF';
-                                    string_buffer[bytes++] = '\xBD';
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xEF');
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBF');
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBD');
                                }

                                // write buffer and reset index; there must be 13 bytes
@@ -973,7 +1054,7 @@ class serializer
            {
                case error_handler_t::strict:
                {
-                    JSON_THROW(type_error::create(316, concat("incomplete UTF-8 string; last byte: 0x", detail::hex_byte(static_cast<std::uint8_t>(s[s.size() - 1]))), nullptr));
+                    JSON_THROW(type_error::create(316, concat("incomplete UTF-8 string; last byte: 0x", hex_bytes(static_cast<std::uint8_t>(s[s.size() - 1] | 0))), nullptr));
                }

                case error_handler_t::ignore:
@@ -1194,6 +1275,20 @@ class serializer
        }
    }

+    /*!
+     * @brief convert a byte to a uppercase hex representation
+     * @param[in] byte byte to represent
+     * @return representation ("00".."FF")
+     */
+    static std::string hex_bytes(std::uint8_t byte)
+    {
+        std::string result = "FF";
+        constexpr const char* nibble_to_hex = "0123456789ABCDEF";
+        result[0] = nibble_to_hex[byte / 16];
+        result[1] = nibble_to_hex[byte % 16];
+        return result;
+    }
+
    /*!
     * @brief write a lowercase "\uXXXX" escape sequence into @a string_buffer
     *
@@ -1307,7 +1402,7 @@ class serializer
    /*!
    @brief dump an integer

-    Dump a given integer, appending it to @ref write_buffer. Works internally with
+    Dump a given integer to output stream @a o. Works internally with
    @a number_buffer.

    @param[in] x  integer number (signed or unsigned) to dump
@@ -1344,7 +1439,7 @@ class serializer
        }

        // use a pointer to fill the buffer
-        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto)
+        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto,cppcoreguidelines-pro-type-vararg,hicpp-vararg)

        number_unsigned_t abs_value;

@@ -1398,7 +1493,7 @@ class serializer
    /*!
    @brief dump a floating-point number

-    Dump a given floating-point number, appending it to @ref write_buffer. Works internally
+    Dump a given floating-point number to output stream @a o. Works internally
    with @a number_buffer.

    @param[in] x  floating-point number to dump
@@ -1518,7 +1613,7 @@ class serializer
     */
    number_unsigned_t remove_sign(number_integer_t x) noexcept
    {
-        JSON_ASSERT(x < 0);
+        JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)()); // NOLINT(misc-redundant-expression)
        return static_cast<number_unsigned_t>(-(x + 1)) + 1;
    }

@@ -3,7 +3,6 @@
 // |  |  |__   |  |  | | | |  version 3.12.0
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
-// SPDX-FileCopyrightText: 2008, 2009 Björn Hoehrmann <bjoern@hoehrmann.de>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT

@@ -37,16 +36,6 @@ StringType to_string(std::size_t value)
    return result;
 }

-/// @return a byte as two uppercase hexadecimal digits
-inline std::string hex_byte(const std::uint8_t byte)
-{
-    std::string result = "00";
-    constexpr const char* nibble_to_hex = "0123456789ABCDEF";
-    result[0] = nibble_to_hex[byte / 16];
-    result[1] = nibble_to_hex[byte % 16];
-    return result;
-}
-
 ///////////////////
 // UTF-8 decoding //
 ///////////////////
@@ -6199,7 +6199,6 @@ NLOHMANN_JSON_NAMESPACE_END
 // |  |  |__   |  |  | | | |  version 3.12.0
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
-// SPDX-FileCopyrightText: 2008, 2009 Björn Hoehrmann <bjoern@hoehrmann.de>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT

@@ -6235,16 +6234,6 @@ StringType to_string(std::size_t value)
    return result;
 }

-/// @return a byte as two uppercase hexadecimal digits
-inline std::string hex_byte(const std::uint8_t byte)
-{
-    std::string result = "00";
-    constexpr const char* nibble_to_hex = "0123456789ABCDEF";
-    result[0] = nibble_to_hex[byte / 16];
-    result[1] = nibble_to_hex[byte % 16];
-    return result;
-}
-
 ///////////////////
 // UTF-8 decoding //
 ///////////////////
@@ -8616,12 +8605,14 @@ 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[out] out    the parsed value on success
+@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
 */
-inline bool parse_float_fast(const char* first, const char* last, double& out) noexcept
+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
@@ -8632,6 +8623,7 @@ inline bool parse_float_fast(const char* first, const char* last, double& out) n
    // 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
@@ -8670,7 +8662,7 @@ inline bool parse_float_fast(const char* first, const char* last, double& out) n
            ++num_digits;
            fractional_digits += static_cast<int>(seen_dot);
        }
-        else if (c == '.')
+        else if (static_cast<DecimalPointType>(c) == decimal_point)
        {
            if (JSON_HEDLEY_UNLIKELY(seen_dot))
            {
@@ -8755,8 +8747,8 @@ inline bool parse_float_fast(const char* first, const char* last, double& out) n
 }

 /// fast float path is only exact for `double`; decline for float/long double
-template<typename FloatType>
-bool parse_float_fast(const char* /*first*/, const char* /*last*/, FloatType& /*out*/) noexcept
+template<typename DecimalPointType, typename FloatType>
+bool parse_float_fast(const char* /*first*/, const char* /*last*/, DecimalPointType /*decimal_point*/, FloatType& /*out*/) noexcept
 {
    return false;
 }
@@ -8768,7 +8760,9 @@ 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)). An under-/overflow (result_out_of_range) also declines, so
+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).

@@ -9309,6 +9303,7 @@ class lexer : public lexer_base<BasicJsonType>
    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false, bool discard_number_values_ = false) noexcept
        : ia(std::move(adapter))
        , ignore_comments(ignore_comments_)
+        , decimal_point_char(static_cast<char_int_type>(get_decimal_point()))
        , discard_number_values(discard_number_values_)
    {}

@@ -9324,7 +9319,8 @@ class lexer : public lexer_base<BasicJsonType>
    // locales
    /////////////////////

-    /// return the decimal point of the current locale
+    /// return the locale-dependent decimal point
+    JSON_HEDLEY_PURE
    static char get_decimal_point() noexcept
    {
        const auto* loc = localeconv();
@@ -10193,10 +10189,9 @@ class lexer : public lexer_base<BasicJsonType>
            token_type::value_float if number could be successfully scanned,
            token_type::parse_error otherwise

-    @note The scanner is independent of the current locale: token_buffer
-          always holds `.`. Only the std::strtod fallback of convert_number()
-          depends on the locale, and it looks up the decimal point right
-          before converting (see convert_float_locale_aware()).
+    @note The scanner is independent of the current locale. Internally, the
+          locale's decimal point is used instead of `.` to work with the
+          locale-dependent converters.
    */
    token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
    {
@@ -10285,7 +10280,7 @@ scan_number_zero:
        {
            case '.':
            {
-                add(current);
+                add(decimal_point_char);
                decimal_point_position = token_buffer.size() - 1;
                goto scan_number_decimal1;
            }
@@ -10322,7 +10317,7 @@ scan_number_any1:

            case '.':
            {
-                add(current);
+                add(decimal_point_char);
                decimal_point_position = token_buffer.size() - 1;
                goto scan_number_decimal1;
            }
@@ -10564,9 +10559,9 @@ scan_number_done:

        // Only a number below 1 can carry further insignificant zeros, and only
        // while the count stays at the limit does removing them change the
-        // answer - so this loop is skipped for all but a few tokens. The
-        // fraction is located through decimal_point_position rather than by
-        // searching '.'.
+        // answer - so this loop is skipped for all but a few tokens. Note
+        // token_buffer holds the locale's decimal point, so the fraction is
+        // located through decimal_point_position rather than by searching '.'.
        if (lead_zero != 0)
        {
            JSON_ASSERT(has_dot != 0); // an integer "0" cannot reach the limit
@@ -10584,8 +10579,8 @@ scan_number_done:
    @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 '.'
-    as decimal point, independent of the locale. Integers are parsed first and fall
+    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.

@@ -10665,7 +10660,7 @@ scan_number_done:
        // 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/strtold.
+        // locale-aware strtof/strtod.
        if (parse_float_from_chars(num_begin, num_end, value_float))
        {
            return token_type::value_float;
@@ -10674,75 +10669,26 @@ scan_number_done:
        // extra pass over the token's bytes, which otherwise shows up on
        // high-precision inputs such as canada.json
        if (mantissa_fits_clinger(mantissa_end)
-                && parse_float_fast(num_begin, num_end, value_float))
+                && parse_float_fast(num_begin, num_end, decimal_point_char, value_float))
        {
            return token_type::value_float;
        }

-        convert_float_locale_aware();
+        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
+        JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
+
        return token_type::value_float;
    }

-    /*!
-    @brief convert the float in token_buffer with strtof/strtod/strtold
-
-    These functions expect the decimal point of the *current* locale, so it is
-    looked up right before the conversion instead of once when the lexer is
-    constructed: a locale change in between (by a parser callback, a SAX
-    handler, or another thread) must not truncate the value (#5198). The
-    token has been validated before, so if the conversion stops early and the
-    decimal point changed in the meantime, the locale changed between the
-    lookup and the call, and the conversion is repeated with the new decimal
-    point. If the decimal point did not change, a retry cannot succeed: the
-    locale's decimal point is not a single character (e.g., the two-byte
-    U+066B of ar_EG.UTF-8 or fa_IR.UTF-8) and cannot be substituted in place.
-    The value strtod parsed up to that point is kept, as before this change.
-
-    Note that changing the locale in another thread *while* strtod runs is
-    undefined behavior of the C library, which this function cannot prevent.
-    */
-    void convert_float_locale_aware()
-    {
-        const bool has_dot = decimal_point_position != std::string::npos;
-        char decimal_point = get_decimal_point();
-        for (;;)
-        {
-            const bool substitute = has_dot && decimal_point != '.';
-            if (substitute)
-            {
-                token_buffer[decimal_point_position] = static_cast<typename string_t::value_type>(decimal_point);
-            }
-
-            char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-            strtof(value_float, token_buffer.data(), &endptr);
-
-            if (substitute)
-            {
-                // get_string() hands the token to the SAX interface with '.'
-                token_buffer[decimal_point_position] = '.';
-            }
-
-            if (JSON_HEDLEY_LIKELY(endptr == token_buffer.data() + token_buffer.size()))
-            {
-                return;
-            }
-
-            // retry only if the locale changed; otherwise, this would loop forever
-            const char current_decimal_point = get_decimal_point();
-            if (current_decimal_point == decimal_point)
-            {
-                return;
-            }
-            decimal_point = current_decimal_point;
-        }
-    }
-
    /*!
    @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
-    (as scan_number() does) and
+    (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
@@ -10858,11 +10804,16 @@ scan_number_done:
        }
 #endif

-        // materialize the token exactly as scan_number() would. reset() already
-        // cleared token_buffer, so append() fills it (assign() is avoided
-        // because custom string_t types need not provide it)
+        // 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)
        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), len);
-        decimal_point_position = dot_index;
+        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;
+        }

        ia.bulk_skip(len - 1);
        position.chars_read_total += (len - 1);
@@ -11129,7 +11080,11 @@ scan_number_done:
    /// return current string value (implicitly resets the token; useful only once)
    string_t& get_string()
    {
-        // a number token holds '.' regardless of the locale (#4084)
+        // translate decimal points from locale back to '.' (#4084)
+        if (decimal_point_char != '.' && decimal_point_position != std::string::npos)
+        {
+            token_buffer[decimal_point_position] = '.';
+        }
        return token_buffer;
    }

@@ -11425,7 +11380,9 @@ scan_number_done:
    number_unsigned_t value_unsigned = 0;
    number_float_t value_float = 0;

-    /// the position of the decimal point in token_buffer
+    /// the decimal point
+    const char_int_type decimal_point_char = '.';
+    /// the position of the decimal point in the input
    std::size_t decimal_point_position = std::string::npos;

    /// whether the caller (e.g. accept()/json_sax_acceptor) only needs the
@@ -14102,80 +14059,6 @@ class binary_reader
        }
    }

-    /*!
-    @brief reads a CBOR object key
-
-    RFC 8949 allows any data item as a map key, but only strings have a
-    counterpart in JSON. A key of any other type is rejected with a message
-    naming that type, rather than the one @ref get_cbor_string gives for a
-    malformed string.
-
-    @param[out] result  created key
-
-    @return whether key creation completed
-    */
-    bool get_cbor_object_key(string_t& result)
-    {
-        // EOF and major type 3 (text string) are left to get_cbor_string
-        if (current == char_traits<char_type>::eof() || (static_cast<unsigned int>(current) & 0xE0u) == 0x60u)
-        {
-            return get_cbor_string(result);
-        }
-
-        const char* found = nullptr;
-        switch (static_cast<unsigned int>(current) >> 5u)
-        {
-            case 0:
-                found = "an unsigned integer";
-                break;
-            case 1:
-                found = "a negative integer";
-                break;
-            case 2:
-                found = "a byte string";
-                break;
-            case 4:
-                found = "an array";
-                break;
-            case 5:
-                found = "a map";
-                break;
-            case 6:
-                found = "a tag";
-                break;
-            default: // major type 7
-                switch (current)
-                {
-                    case 0xF4:
-                    case 0xF5:
-                        found = "a boolean";
-                        break;
-                    case 0xF6:
-                        found = "null";
-                        break;
-                    case 0xF7:
-                        found = "undefined";
-                        break;
-                    case 0xF9:
-                    case 0xFA:
-                    case 0xFB:
-                        found = "a floating-point number";
-                        break;
-                    case 0xFF:
-                        found = "a break stop code";
-                        break;
-                    default:
-                        found = "a simple value";
-                        break;
-                }
-                break;
-        }
-
-        auto last_token = get_token_string();
-        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
-                                exception_message(input_format_t::cbor, concat("only string keys are supported, but found ", found, "; last byte: 0x", last_token), "object key"), nullptr));
-    }
-
    /*!
    @brief reads a definite-length CBOR byte array

@@ -14420,7 +14303,7 @@ class binary_reader
                if (top.is_object)
                {
                    key.clear();
-                    if (JSON_HEDLEY_UNLIKELY(!get_cbor_object_key(key) || !sax->key(key)))
+                    if (JSON_HEDLEY_UNLIKELY(!get_cbor_string(key) || !sax->key(key)))
                    {
                        return false;
                    }
@@ -14921,98 +14804,6 @@ class binary_reader
        }
    }

-    /*!
-    @brief reads a MessagePack object key
-
-    The MessagePack specification allows any type as a map key, but only
-    strings have a counterpart in JSON. A key of any other type is rejected
-    with a message naming that type, rather than the one @ref
-    get_msgpack_string gives for a malformed string.
-
-    @param[out] result  created key
-
-    @return whether key creation completed
-    */
-    bool get_msgpack_object_key(string_t& result)
-    {
-        const char* found = nullptr;
-        switch (current)
-        {
-            case 0xC0:
-                found = "nil";
-                break;
-            case 0xC2:
-            case 0xC3:
-                found = "a boolean";
-                break;
-            case 0xCA:
-            case 0xCB:
-                found = "a float";
-                break;
-            case 0xC4:
-            case 0xC5:
-            case 0xC6:
-                found = "a bin";
-                break;
-            case 0xC7:
-            case 0xC8:
-            case 0xC9:
-            case 0xD4:
-            case 0xD5:
-            case 0xD6:
-            case 0xD7:
-            case 0xD8:
-                found = "an ext";
-                break;
-            case 0xCC:
-            case 0xCD:
-            case 0xCE:
-            case 0xCF:
-            case 0xD0:
-            case 0xD1:
-            case 0xD2:
-            case 0xD3:
-                found = "an integer";
-                break;
-            case 0xDC:
-            case 0xDD:
-                found = "an array";
-                break;
-            case 0xDE:
-            case 0xDF:
-                found = "a map";
-                break;
-            default:
-                // fixint, fixmap, and fixarray; strings, EOF, and the unused
-                // byte 0xC1 are left to get_msgpack_string
-                if (current == char_traits<char_type>::eof())
-                {
-                    return get_msgpack_string(result);
-                }
-                if (current <= 0x7F || current >= 0xE0)
-                {
-                    found = "an integer";
-                }
-                else if (current <= 0x8F)
-                {
-                    found = "a map";
-                }
-                else if (current <= 0x9F)
-                {
-                    found = "an array";
-                }
-                else
-                {
-                    return get_msgpack_string(result);
-                }
-                break;
-        }
-
-        auto last_token = get_token_string();
-        return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
-                                exception_message(input_format_t::msgpack, concat("only string keys are supported, but found ", found, "; last byte: 0x", last_token), "object key"), nullptr));
-    }
-
    /*!
    @brief reads a MessagePack byte array

@@ -15175,7 +14966,7 @@ class binary_reader
                {
                    get();
                    key.clear();
-                    if (JSON_HEDLEY_UNLIKELY(!get_msgpack_object_key(key) || !sax->key(key)))
+                    if (JSON_HEDLEY_UNLIKELY(!get_msgpack_string(key) || !sax->key(key)))
                    {
                        return false;
                    }
@@ -20157,7 +19948,9 @@ NLOHMANN_JSON_NAMESPACE_END



+#include <algorithm> // copy
 #include <cstddef> // size_t
+#include <iterator> // back_inserter
 #include <memory> // shared_ptr, make_shared
 #include <string> // basic_string
 #include <utility> // move
@@ -20179,10 +19972,6 @@ namespace detail
 template<typename CharType> struct output_adapter_protocol
 {
    virtual void write_character(CharType c) = 0;
-    /// @param[in] s      pointer to the characters to write; binary_writer legitimately
-    ///                   passes a null pointer together with length 0 for an empty
-    ///                   string or binary value, so implementations must tolerate that
-    /// @param[in] length number of characters at @a s
    virtual void write_characters(const CharType* s, std::size_t length) = 0;
    virtual ~output_adapter_protocol() = default;

@@ -20249,6 +20038,7 @@ class output_vector_adapter : public output_adapter_protocol<CharType>
        sink.write_character(c);
    }

+    JSON_HEDLEY_NON_NULL(2)
    void write_characters(const CharType* s, std::size_t length) override
    {
        sink.write_characters(s, length);
@@ -20273,6 +20063,7 @@ class output_stream_adapter : public output_adapter_protocol<CharType>
        stream.put(c);
    }

+    JSON_HEDLEY_NON_NULL(2)
    void write_characters(const CharType* s, std::size_t length) override
    {
        stream.write(s, static_cast<std::streamsize>(length));
@@ -20297,6 +20088,7 @@ class output_string_adapter : public output_adapter_protocol<CharType>
        str.push_back(c);
    }

+    JSON_HEDLEY_NON_NULL(2)
    void write_characters(const CharType* s, std::size_t length) override
    {
        str.append(s, length);
@@ -20369,8 +20161,6 @@ NLOHMANN_JSON_NAMESPACE_END

 // #include <nlohmann/detail/string_concat.hpp>

-// #include <nlohmann/detail/string_utils.hpp>
-

 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -22620,10 +22410,20 @@ class binary_writer
        const std::size_t valid = valid_utf8_prefix(data, s.size());
        if (JSON_HEDLEY_UNLIKELY(valid != s.size()))
        {
-            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(valid), ": 0x", detail::hex_byte(data[valid])), &context));
+            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(valid), ": 0x", hex_byte(data[valid])), &context));
        }
    }

+    /// @return a byte as two uppercase hexadecimal digits
+    static std::string hex_byte(const std::uint8_t byte)
+    {
+        std::string result = "00";
+        constexpr const char* nibble_to_hex = "0123456789ABCDEF";
+        result[0] = nibble_to_hex[byte / 16];
+        result[1] = nibble_to_hex[byte % 16];
+        return result;
+    }
+
    /*!
    @brief write an integer in the shortest encoding

@@ -22956,23 +22756,24 @@ NLOHMANN_JSON_NAMESPACE_END
 // |  |  |__   |  |  | | | |  version 3.12.0
 // |_____|_____|_____|_|___|  https://github.com/nlohmann/json
 //
+// SPDX-FileCopyrightText: 2008, 2009 Björn Hoehrmann <bjoern@hoehrmann.de>
 // SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
 // SPDX-License-Identifier: MIT



-#include <algorithm> // remove, fill, find, none_of, min
+#include <algorithm> // reverse, remove, fill, find, none_of, min
 #include <array> // array
 #include <clocale> // localeconv, lconv
-#include <cmath> // isfinite
+#include <cmath> // labs, isfinite, isnan, signbit
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // uint8_t
 #include <cstdio> // snprintf
 #include <cstring> // memcpy, memset
-#include <iterator> // next
 #include <limits> // numeric_limits
 #include <string> // string, char_traits
 #include <type_traits> // is_same
+#include <utility> // move
 #include <vector> // vector

 // #include <nlohmann/detail/conversions/to_chars.hpp>
@@ -24104,6 +23905,8 @@ NLOHMANN_JSON_NAMESPACE_END

 // #include <nlohmann/detail/meta/cpp_future.hpp>

+// #include <nlohmann/detail/output/binary_writer.hpp>
+
 // #include <nlohmann/detail/output/output_adapters.hpp>

 // #include <nlohmann/detail/recursion_depth_limit.hpp>
@@ -24186,10 +23989,9 @@ class serializer
    additional parameter. Arrays and objects are serialized without recursion,
    however deeply they are nested.

-    - strings and object keys are escaped using @ref dump_escaped
-    - integer numbers are converted using a digit-pair lookup table (@ref dump_integer)
-    - floating-point numbers are converted to a string using @ref dump_float, which
-      uses `to_chars` for IEEE-754 types and `snprintf` otherwise
+    - strings and object keys are escaped using `escape_string()`
+    - integer numbers are converted implicitly via `operator<<`
+    - floating-point numbers are converted to a string using `"%g"` format
    - binary values are serialized as objects containing the subtype and the
      byte array

@@ -24364,16 +24166,127 @@ class serializer
            }

            case value_t::string:
-            case value_t::binary:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::discarded:
-            case value_t::null:
-            default:
-                dump_scalar(val, current_indent);
+            {
+                put_char('"');
+                dump_escaped(*val.m_data.m_value.string);
+                put_char('"');
                return;
+            }
+
+            case value_t::binary:
+            {
+                if (pretty_print)
+                {
+                    put_literal("{\n");
+
+                    // variable to hold indentation for recursive calls
+                    const auto new_indent = next_indent(current_indent, indent_step);
+
+                    put_indent(new_indent);
+
+                    put_literal("\"bytes\": [");
+
+                    if (!val.m_data.m_value.binary->empty())
+                    {
+                        for (auto i = val.m_data.m_value.binary->cbegin();
+                                i != val.m_data.m_value.binary->cend() - 1; ++i)
+                        {
+                            dump_byte(*i);
+                            put_literal(", ");
+                        }
+                        dump_byte(val.m_data.m_value.binary->back());
+                    }
+
+                    put_literal("],\n");
+                    put_indent(new_indent);
+
+                    put_literal("\"subtype\": ");
+                    if (val.m_data.m_value.binary->has_subtype())
+                    {
+                        dump_integer(val.m_data.m_value.binary->subtype());
+                    }
+                    else
+                    {
+                        put_literal("null");
+                    }
+                    put_char('\n');
+                    put_indent(current_indent);
+                    put_char('}');
+                }
+                else
+                {
+                    put_literal("{\"bytes\":[");
+
+                    if (!val.m_data.m_value.binary->empty())
+                    {
+                        for (auto i = val.m_data.m_value.binary->cbegin();
+                                i != val.m_data.m_value.binary->cend() - 1; ++i)
+                        {
+                            dump_byte(*i);
+                            put_char(',');
+                        }
+                        dump_byte(val.m_data.m_value.binary->back());
+                    }
+
+                    put_literal("],\"subtype\":");
+                    if (val.m_data.m_value.binary->has_subtype())
+                    {
+                        dump_integer(val.m_data.m_value.binary->subtype());
+                        put_char('}');
+                    }
+                    else
+                    {
+                        put_literal("null}");
+                    }
+                }
+                return;
+            }
+
+            case value_t::boolean:
+            {
+                if (val.m_data.m_value.boolean)
+                {
+                    put_literal("true");
+                }
+                else
+                {
+                    put_literal("false");
+                }
+                return;
+            }
+
+            case value_t::number_integer:
+            {
+                dump_integer(val.m_data.m_value.number_integer);
+                return;
+            }
+
+            case value_t::number_unsigned:
+            {
+                dump_integer(val.m_data.m_value.number_unsigned);
+                return;
+            }
+
+            case value_t::number_float:
+            {
+                dump_float(val.m_data.m_value.number_float);
+                return;
+            }
+
+            case value_t::discarded:
+            {
+                put_literal("<discarded>");
+                return;
+            }
+
+            case value_t::null:
+            {
+                put_literal("null");
+                return;
+            }
+
+            default:            // LCOV_EXCL_LINE
+                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
        }
    }

@@ -24530,9 +24443,9 @@ class serializer
    @brief serialize the value @a val, but not the elements of a container

    An object or array with elements is opened and pushed onto @a stack for
-    @ref dump_iteratively to walk; everything else - including a binary value,
+    @ref dump_internal to walk; everything else - including a binary value,
    which looks like an object but has no elements to descend into - is written
-    out in full by @ref dump_scalar.
+    out here in full.
    */
    void dump_value(const BasicJsonType& val,
                    const std::size_t current_indent,
@@ -24590,35 +24503,6 @@ class serializer
                return;
            }

-            case value_t::string:
-            case value_t::binary:
-            case value_t::boolean:
-            case value_t::number_integer:
-            case value_t::number_unsigned:
-            case value_t::number_float:
-            case value_t::discarded:
-            case value_t::null:
-            default:
-                dump_scalar(val, current_indent);
-                return;
-        }
-    }
-
-    /*!
-    @brief serialize the value @a val, which is neither an object nor an array
-
-    Shared by @ref dump_internal and @ref dump_value, so that a value is written
-    the same way however deeply it is nested. A binary value is written out here
-    in full: it looks like an object, but has no elements to descend into.
-
-    @param[in] val             value to serialize; not an object or array
-    @param[in] current_indent  the indentation of @a val, used for a
-                               pretty-printed binary value
-    */
-    void dump_scalar(const BasicJsonType& val, const std::size_t current_indent)
-    {
-        switch (val.m_data.m_type)
-        {
            case value_t::string:
            {
                put_char('"');
@@ -24739,8 +24623,6 @@ class serializer
                return;
            }

-            case value_t::object: // LCOV_EXCL_LINE
-            case value_t::array:  // LCOV_EXCL_LINE
            default:            // LCOV_EXCL_LINE
                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
        }
@@ -24769,7 +24651,7 @@ class serializer
    Escape a string by replacing certain special characters by a sequence of an
    escape character (backslash) and another character and other control
    characters by a sequence of "\u" followed by a four-digit hex
-    representation. The escaped string is appended to @ref write_buffer.
+    representation. The escaped string is written to output stream @a o.

    @param[in] s  the string to escape

@@ -24963,7 +24845,7 @@ class serializer
                    {
                        case error_handler_t::strict:
                        {
-                            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", detail::hex_byte(byte)), nullptr));
+                            JSON_THROW(type_error::create(316, concat("invalid UTF-8 byte at index ", std::to_string(i), ": 0x", hex_bytes(byte | 0)), nullptr));
                        }

                        case error_handler_t::ignore:
@@ -24996,9 +24878,9 @@ class serializer
                                }
                                else
                                {
-                                    string_buffer[bytes++] = '\xEF';
-                                    string_buffer[bytes++] = '\xBF';
-                                    string_buffer[bytes++] = '\xBD';
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xEF');
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBF');
+                                    string_buffer[bytes++] = detail::binary_writer<BasicJsonType, char>::to_char_type('\xBD');
                                }

                                // write buffer and reset index; there must be 13 bytes
@@ -25055,7 +24937,7 @@ class serializer
            {
                case error_handler_t::strict:
                {
-                    JSON_THROW(type_error::create(316, concat("incomplete UTF-8 string; last byte: 0x", detail::hex_byte(static_cast<std::uint8_t>(s[s.size() - 1]))), nullptr));
+                    JSON_THROW(type_error::create(316, concat("incomplete UTF-8 string; last byte: 0x", hex_bytes(static_cast<std::uint8_t>(s[s.size() - 1] | 0))), nullptr));
                }

                case error_handler_t::ignore:
@@ -25276,6 +25158,20 @@ class serializer
        }
    }

+    /*!
+     * @brief convert a byte to a uppercase hex representation
+     * @param[in] byte byte to represent
+     * @return representation ("00".."FF")
+     */
+    static std::string hex_bytes(std::uint8_t byte)
+    {
+        std::string result = "FF";
+        constexpr const char* nibble_to_hex = "0123456789ABCDEF";
+        result[0] = nibble_to_hex[byte / 16];
+        result[1] = nibble_to_hex[byte % 16];
+        return result;
+    }
+
    /*!
     * @brief write a lowercase "\uXXXX" escape sequence into @a string_buffer
     *
@@ -25389,7 +25285,7 @@ class serializer
    /*!
    @brief dump an integer

-    Dump a given integer, appending it to @ref write_buffer. Works internally with
+    Dump a given integer to output stream @a o. Works internally with
    @a number_buffer.

    @param[in] x  integer number (signed or unsigned) to dump
@@ -25426,7 +25322,7 @@ class serializer
        }

        // use a pointer to fill the buffer
-        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto)
+        auto buffer_ptr = number_buffer.begin(); // NOLINT(llvm-qualified-auto,readability-qualified-auto,cppcoreguidelines-pro-type-vararg,hicpp-vararg)

        number_unsigned_t abs_value;

@@ -25480,7 +25376,7 @@ class serializer
    /*!
    @brief dump a floating-point number

-    Dump a given floating-point number, appending it to @ref write_buffer. Works internally
+    Dump a given floating-point number to output stream @a o. Works internally
    with @a number_buffer.

    @param[in] x  floating-point number to dump
@@ -25600,7 +25496,7 @@ class serializer
     */
    number_unsigned_t remove_sign(number_integer_t x) noexcept
    {
-        JSON_ASSERT(x < 0);
+        JSON_ASSERT(x < 0 && x < (std::numeric_limits<number_integer_t>::max)()); // NOLINT(misc-redundant-expression)
        return static_cast<number_unsigned_t>(-(x + 1)) + 1;
    }

@@ -1830,51 +1830,10 @@ TEST_CASE("CBOR")
        SECTION("invalid string in map")
        {
            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xa1, 0xff, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR object key: only string keys are supported, but found a break stop code; last byte: 0xFF", json::parse_error&);
+            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xa1, 0xff, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xFF", json::parse_error&);
            CHECK(json::from_cbor(std::vector<uint8_t>({0xa1, 0xff, 0x01}), true, false).is_discarded());
        }

-        SECTION("non-string key (see #2766 and #3381)")
-        {
-            // only text strings map to JSON object keys; any other key is
-            // rejected with a message naming its type
-            const std::vector<std::pair<std::vector<std::uint8_t>, std::string>> cases =
-            {
-                {{0xA1, 0x01, 0x01}, "an unsigned integer; last byte: 0x01"},
-                {{0xA1, 0x20, 0x01}, "a negative integer; last byte: 0x20"},
-                {{0xA1, 0x41, 0x61, 0x01}, "a byte string; last byte: 0x41"},
-                {{0xA1, 0x80, 0x01}, "an array; last byte: 0x80"},
-                {{0xA1, 0xA0, 0x01}, "a map; last byte: 0xA0"},
-                {{0xA1, 0xC0, 0x61, 0x61, 0x01}, "a tag; last byte: 0xC0"},
-                {{0xA1, 0xF4, 0x01}, "a boolean; last byte: 0xF4"},
-                {{0xA1, 0xF5, 0x01}, "a boolean; last byte: 0xF5"},
-                {{0xA1, 0xF6, 0x01}, "null; last byte: 0xF6"},
-                {{0xA1, 0xF7, 0x01}, "undefined; last byte: 0xF7"},
-                {{0xA1, 0xF9, 0x3C, 0x00, 0x01}, "a floating-point number; last byte: 0xF9"},
-                {{0xA1, 0xFA, 0x3F, 0x80, 0x00, 0x00, 0x01}, "a floating-point number; last byte: 0xFA"},
-                {{0xA1, 0xFB, 0x3F, 0xF0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "a floating-point number; last byte: 0xFB"},
-                {{0xA1, 0xE0, 0x01}, "a simple value; last byte: 0xE0"},
-                {{0xA1, 0xF8, 0x20, 0x01}, "a simple value; last byte: 0xF8"},
-                // indefinite-length map
-                {{0xBF, 0x01, 0x01, 0xFF}, "an unsigned integer; last byte: 0x01"},
-            };
-
-            for (const auto& c : cases)
-            {
-                CAPTURE(c.first)
-                const std::string expected = "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR object key: only string keys are supported, but found " + c.second;
-                json _;
-                CHECK_THROWS_WITH_AS(_ = json::from_cbor(c.first), expected.c_str(), json::parse_error&);
-                CHECK(json::from_cbor(c.first, true, false).is_discarded());
-            }
-
-            // a key of major type 3 with a reserved length is still reported as
-            // a malformed string, and a missing key as the end of input
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1})), "[json.exception.parse_error.110] parse error at byte 2: syntax error while parsing CBOR string: unexpected end of input", json::parse_error&);
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1, 0x7C, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x7C", json::parse_error&);
-        }
-
        SECTION("invalid UTF-8 in string (see #5529)")
        {
            // a two-character text string (major type 3) whose bytes are not
@@ -2325,7 +2284,7 @@ TEST_CASE("CBOR indefinite-length strings do not recurse per chunk")
    SECTION("a break marker outside an indefinite-length string is not a string")
    {
        // 0xFF only closes a string that was opened; on its own it is not one
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1, 0xFF, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR object key: only string keys are supported, but found a break stop code; last byte: 0xFF", json::parse_error&);
+        CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1, 0xFF, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xFF", json::parse_error&);
    }
 }

@@ -666,7 +666,7 @@ TEST_CASE("parse_float_fast declines what it cannot convert exactly")
    // always safe: the caller then falls back to a slower, exact conversion.
    const auto fast = [](const std::string & s, double & out)
    {
-        return nlohmann::detail::parse_float_fast(s.data(), s.data() + s.size(), out);
+        return nlohmann::detail::parse_float_fast(s.data(), s.data() + s.size(), '.', out);
    };
    double out = 0;

@@ -12,12 +12,7 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;

-#include <array>
 #include <clocale>
-#include <map>
-#include <string>
-#include <utility>
-#include <vector>

 struct ParserImpl final: public nlohmann::json_sax<json>
 {
@@ -180,208 +175,3 @@ TEST_CASE("locale-dependent test (LC_NUMERIC=de_DE)")
        MESSAGE("locale de_DE is not usable");
    }
 }
-
-namespace
-{
-// records the numbers of a flat array and switches LC_NUMERIC to the given
-// locale once the array opens - after the lexer was constructed, but before
-// any number in the array is lexed
-struct LocaleSwitchingSax final: public nlohmann::json_sax<json>
-{
-    explicit LocaleSwitchingSax(const char* switch_to)
-        : locale_after_open(switch_to)
-    {}
-
-    bool null() override
-    {
-        return true;
-    }
-    bool boolean(bool /*val*/) override
-    {
-        return true;
-    }
-    bool number_integer(json::number_integer_t /*val*/) override
-    {
-        return true;
-    }
-    bool number_unsigned(json::number_unsigned_t /*val*/) override
-    {
-        return true;
-    }
-    bool number_float(json::number_float_t val, const json::string_t& s) override
-    {
-        values.push_back(val);
-        strings.push_back(s);
-        return true;
-    }
-    bool string(json::string_t& /*val*/) override
-    {
-        return true;
-    }
-    bool binary(json::binary_t& /*val*/) override
-    {
-        return true;
-    }
-    bool start_object(std::size_t /*val*/) override
-    {
-        return true;
-    }
-    bool key(json::string_t& /*val*/) override
-    {
-        return true;
-    }
-    bool end_object() override
-    {
-        return true;
-    }
-    bool start_array(std::size_t /*val*/) override
-    {
-        switched = std::setlocale(LC_NUMERIC, locale_after_open.c_str()) != nullptr;
-        return true;
-    }
-    bool end_array() override
-    {
-        return true;
-    }
-    bool parse_error(std::size_t /*val*/, const std::string& /*val*/, const nlohmann::detail::exception& /*val*/) override
-    {
-        return false;
-    }
-
-    std::string locale_after_open;
-    bool switched = false;
-    std::vector<json::number_float_t> values {}; // NOLINT(readability-redundant-member-init)
-    std::vector<json::string_t> strings {}; // NOLINT(readability-redundant-member-init)
-};
-} // namespace
-
-TEST_CASE("locale changes between lexer construction and number conversion (#5198)")
-{
-    // The numbers are chosen so that the conversion also takes the strtod
-    // fallback, which honors the locale that is current at conversion time:
-    // too many significant digits for Clinger's fast path, an underflow that
-    // std::from_chars rejects, and a plain value.
-    const std::vector<std::string> numbers = {"3.14159265358979323846", "1.5e-400", "12.34", "-0.000123456789012345678"};
-    std::string text = "[";
-    for (const auto& n : numbers)
-    {
-        text += (text.size() == 1 ? "" : ",") + n;
-    }
-    text += "]";
-
-    using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
-
-    // reference values, parsed without a locale switch
-    REQUIRE(std::setlocale(LC_NUMERIC, "C") != nullptr);
-    const json expected = json::parse(text);
-    const long_double_json expected_ld = long_double_json::parse(text);
-
-    const std::array<std::pair<const char*, const char*>, 2> transitions =
-    {
-        {
-            {"C", "de_DE"},
-            {"de_DE", "C"}
-        }
-    };
-
-    for (const auto& transition : transitions)
-    {
-        CAPTURE(transition.first);
-        CAPTURE(transition.second);
-
-        if (std::setlocale(LC_NUMERIC, transition.first) == nullptr)
-        {
-            MESSAGE("locale is not usable");
-            continue;
-        }
-
-        // SAX parsing
-        {
-            LocaleSwitchingSax sax(transition.second);
-            CHECK(json::sax_parse(text, &sax));
-            if (sax.switched)
-            {
-                CHECK(sax.values == expected.get<std::vector<json::number_float_t>>());
-                CHECK(sax.strings == numbers);
-            }
-        }
-
-        // DOM parsing with a callback
-        {
-            bool switched = false;
-            const auto cb = [&](int /*depth*/, json::parse_event_t event, json& /*parsed*/) noexcept
-            {
-                if (event == json::parse_event_t::array_start)
-                {
-                    switched = std::setlocale(LC_NUMERIC, transition.second) != nullptr;
-                }
-                return true;
-            };
-            const json j = json::parse(text, cb);
-            if (switched)
-            {
-                CHECK(j == expected);
-            }
-        }
-
-        // a long double goes through std::strtold unless std::from_chars supports it
-        {
-            bool switched = false;
-            const auto cb = [&](int /*depth*/, long_double_json::parse_event_t event, long_double_json& /*parsed*/) noexcept
-            {
-                if (event == long_double_json::parse_event_t::array_start)
-                {
-                    switched = std::setlocale(LC_NUMERIC, transition.second) != nullptr;
-                }
-                return true;
-            };
-            const long_double_json j = long_double_json::parse(text, cb);
-            if (switched)
-            {
-                CHECK(j == expected_ld);
-            }
-        }
-    }
-
-    CHECK(std::setlocale(LC_NUMERIC, "C") != nullptr);
-}
-
-TEST_CASE("locale with a multi-byte decimal point")
-{
-    // Some locales use a decimal point that is not a single character, e.g.
-    // U+066B ARABIC DECIMAL SEPARATOR (two bytes in UTF-8). It cannot be
-    // substituted in place for '.', so the strtod fallback stops early. The
-    // conversion must still terminate rather than retry forever.
-    const std::array<const char*, 6> names = {{"ar_EG.UTF-8", "ar_SA.UTF-8", "fa_IR.UTF-8", "ps_AF.UTF-8", "ar_EG", "fa_IR"}};
-    bool tested = false;
-    for (const char* name : names)
-    {
-        if (std::setlocale(LC_NUMERIC, name) == nullptr)
-        {
-            continue;
-        }
-        const std::string decimal_point = std::localeconv()->decimal_point;
-        if (decimal_point.size() < 2)
-        {
-            continue;
-        }
-        CAPTURE(name);
-        tested = true;
-
-        // too many significant digits for Clinger's fast path, and an underflow
-        // that std::from_chars rejects: both reach the strtod fallback
-        json j;
-        CHECK_NOTHROW(j = json::parse("[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]"));
-        CHECK(j.is_array());
-        CHECK(json::accept("3.14159265358979323846"));
-
-        // a value the locale-independent paths convert is not affected
-        CHECK(json::parse("12.5") == 12.5);
-    }
-    if (!tested)
-    {
-        MESSAGE("no locale with a multi-byte decimal point is usable");
-    }
-
-    CHECK(std::setlocale(LC_NUMERIC, "C") != nullptr);
-}
@@ -1551,69 +1551,10 @@ TEST_CASE("MessagePack")
        SECTION("invalid string in map")
        {
            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81, 0xff, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack object key: only string keys are supported, but found an integer; last byte: 0xFF", json::parse_error&);
+            CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81, 0xff, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack string: expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0xFF", json::parse_error&);
            CHECK(json::from_msgpack(std::vector<uint8_t>({0x81, 0xff, 0x01}), true, false).is_discarded());
        }

-        SECTION("non-string key (see #3381)")
-        {
-            // only strings map to JSON object keys; any other key is rejected
-            // with a message naming its type
-            const std::vector<std::pair<std::vector<std::uint8_t>, std::string>> cases =
-            {
-                {{0x81, 0xC0, 0x01}, "nil; last byte: 0xC0"},
-                {{0x81, 0xC2, 0x01}, "a boolean; last byte: 0xC2"},
-                {{0x81, 0xC3, 0x01}, "a boolean; last byte: 0xC3"},
-                {{0x81, 0xCA, 0x3F, 0x80, 0x00, 0x00, 0x01}, "a float; last byte: 0xCA"},
-                {{0x81, 0xCB, 0x3F, 0xF0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "a float; last byte: 0xCB"},
-                {{0x81, 0xC4, 0x00, 0x01}, "a bin; last byte: 0xC4"},
-                {{0x81, 0xC5, 0x00, 0x00, 0x01}, "a bin; last byte: 0xC5"},
-                {{0x81, 0xC6, 0x00, 0x00, 0x00, 0x00, 0x01}, "a bin; last byte: 0xC6"},
-                {{0x81, 0xC7, 0x00, 0x01, 0x01}, "an ext; last byte: 0xC7"},
-                {{0x81, 0xC8, 0x00, 0x00, 0x01, 0x01}, "an ext; last byte: 0xC8"},
-                {{0x81, 0xC9, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01}, "an ext; last byte: 0xC9"},
-                {{0x81, 0xD4, 0x01, 0x00, 0x01}, "an ext; last byte: 0xD4"},
-                {{0x81, 0xD5, 0x01, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD5"},
-                {{0x81, 0xD6, 0x01, 0x00, 0x00, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD6"},
-                {{0x81, 0xD7, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD7"},
-                {{0x81, 0xD8, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01}, "an ext; last byte: 0xD8"},
-                {{0x81, 0xCC, 0x01, 0x01}, "an integer; last byte: 0xCC"},
-                {{0x81, 0xCD, 0x00, 0x01, 0x01}, "an integer; last byte: 0xCD"},
-                {{0x81, 0xCE, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xCE"},
-                {{0x81, 0xCF, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xCF"},
-                {{0x81, 0xD0, 0x01, 0x01}, "an integer; last byte: 0xD0"},
-                {{0x81, 0xD1, 0x00, 0x01, 0x01}, "an integer; last byte: 0xD1"},
-                {{0x81, 0xD2, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xD2"},
-                {{0x81, 0xD3, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01}, "an integer; last byte: 0xD3"},
-                {{0x81, 0x00, 0x01}, "an integer; last byte: 0x00"},
-                {{0x81, 0x7F, 0x01}, "an integer; last byte: 0x7F"},
-                {{0x81, 0xE0, 0x01}, "an integer; last byte: 0xE0"},
-                {{0x81, 0x80, 0x01}, "a map; last byte: 0x80"},
-                {{0x81, 0x8F, 0x01}, "a map; last byte: 0x8F"},
-                {{0x81, 0xDE, 0x00, 0x00, 0x01}, "a map; last byte: 0xDE"},
-                {{0x81, 0xDF, 0x00, 0x00, 0x00, 0x00, 0x01}, "a map; last byte: 0xDF"},
-                {{0x81, 0x90, 0x01}, "an array; last byte: 0x90"},
-                {{0x81, 0x9F, 0x01}, "an array; last byte: 0x9F"},
-                {{0x81, 0xDC, 0x00, 0x00, 0x01}, "an array; last byte: 0xDC"},
-                {{0x81, 0xDD, 0x00, 0x00, 0x00, 0x00, 0x01}, "an array; last byte: 0xDD"},
-            };
-
-            for (const auto& c : cases)
-            {
-                CAPTURE(c.first)
-                const std::string expected = "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack object key: only string keys are supported, but found " + c.second;
-                json _;
-                CHECK_THROWS_WITH_AS(_ = json::from_msgpack(c.first), expected.c_str(), json::parse_error&);
-                CHECK(json::from_msgpack(c.first, true, false).is_discarded());
-            }
-
-            json _;
-            // the unused byte 0xC1 is still reported as a malformed string
-            CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81, 0xC1, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack string: expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0xC1", json::parse_error&);
-            // a missing key is still reported as the end of input
-            CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81})), "[json.exception.parse_error.110] parse error at byte 2: syntax error while parsing MessagePack string: unexpected end of input", json::parse_error&);
-        }
-
        SECTION("invalid UTF-8 in string (see #5529)")
        {
            // a fixstr of length 2 (0xA0 | 2) whose bytes are not valid UTF-8
@@ -1018,7 +1018,7 @@ TEST_CASE("regression tests 1")
        };

        json _;
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(vec), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR object key: only string keys are supported, but found an array; last byte: 0x98", json::parse_error&);
+        CHECK_THROWS_WITH_AS(_ = json::from_cbor(vec), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x98", json::parse_error&);

        // related test case: nonempty UTF-8 string (indefinite length)
        std::vector<uint8_t> const vec1 {0x7f, 0x61, 0x61};
@@ -1065,7 +1065,7 @@ TEST_CASE("regression tests 1")
        };

        json _;
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(vec1), "[json.exception.parse_error.113] parse error at byte 13: syntax error while parsing CBOR object key: only string keys are supported, but found a map; last byte: 0xB4", json::parse_error&);
+        CHECK_THROWS_WITH_AS(_ = json::from_cbor(vec1), "[json.exception.parse_error.113] parse error at byte 13: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xB4", json::parse_error&);

        // related test case: double-precision
        std::vector<uint8_t> const vec2
@@ -1077,7 +1077,7 @@ TEST_CASE("regression tests 1")
            0x96, 0x96, 0xb4, 0xb4, 0xfa, 0x94, 0x94, 0x61,
            0x61, 0x61, 0x61, 0x61, 0x61, 0x61, 0x61, 0xfb
        };
-        CHECK_THROWS_WITH_AS(_ = json::from_cbor(vec2), "[json.exception.parse_error.113] parse error at byte 13: syntax error while parsing CBOR object key: only string keys are supported, but found a map; last byte: 0xB4", json::parse_error&);
+        CHECK_THROWS_WITH_AS(_ = json::from_cbor(vec2), "[json.exception.parse_error.113] parse error at byte 13: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xB4", json::parse_error&);
    }

    SECTION("issue #452 - Heap-buffer-overflow (OSS-Fuzz issue 585)")
@@ -241,6 +241,52 @@ class my_allocator : public std::allocator<T>
    };
 };

+/////////////////////////////////////////////////////////////////////
+// for #3669
+/////////////////////////////////////////////////////////////////////
+
+// mimics boost::optional's converting constructor, whose SFINAE check asks
+// whether T is constructible from const U&
+template<class T, class Arg>
+struct issue3669_is_constructible
+{
+    template<class T2, class A2, class = decltype(T2(std::declval<A2>()))>
+    static char test(int);
+    template<class, class>
+    static long test(...);
+    static constexpr bool value = sizeof(test<T, Arg>(0)) == 1;
+};
+
+template<class T>
+class issue3669_optional
+{
+  public:
+    issue3669_optional() = default;
+    template<class U>
+    issue3669_optional(const issue3669_optional<U>& /*unused*/, // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+                       typename std::enable_if<issue3669_is_constructible<T, const U&>::value, bool>::type /*unused*/ = true) {}
+};
+
+class Issue3669Dummy
+{
+  public:
+    explicit Issue3669Dummy(const json& /*unused*/) {}
+};
+
+class Issue3669Holder
+{
+    issue3669_optional<Issue3669Dummy> d{};
+
+    // GCC < 11 (C++11/14) rejects a free to_json(json&, const Issue3669Holder&)
+    // here, because ADL for Issue3669Dummy finds it and closes an instantiation
+    // cycle; a hidden friend is only visible to ADL for Issue3669Holder
+    friend void to_json(json& j, const Issue3669Holder& h)
+    {
+        static_cast<void>(h.d); // silence -Wunused-private-field
+        j = "holder";
+    }
+};
+
 TEST_CASE("regression tests 2")
 {
    SECTION("issue #1001 - Fix memory leak during parser callback")
@@ -766,6 +812,14 @@ TEST_CASE("regression tests 2")
        CHECK(j == k);
    }

+    SECTION("issue #3669 - invalid use of incomplete type with optional member and to_json")
+    {
+        const Issue3669Holder h{};
+        const Issue3669Holder h2(h); // NOLINT(performance-unnecessary-copy-initialization)
+        const json j = h2;
+        CHECK(j == "holder");
+    }
+
 }

 TEST_CASE("regression test - parser callback must not lose a duplicate key's prior value")