Reserve output capacity up front for binary serialization

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

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

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

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

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

docs/mkdocs/docs/api/basic_json/sax_parse.md

@@ -69,8 +69,7 @@ The SAX event lister must follow the interface of [`json_sax`](../json_sax/index
      [`input_format_t`](input_format_t.md) for more information
 
 `strict` (in)
-:   whether the input has to be consumed completely (optional, `#!cpp true` by default); when `#!cpp false` and the
-    input is a `#!cpp std::istream`, the stream is left positioned right after the parsed value
+:   whether the input has to be consumed completely (optional, `#!cpp true` by default)
 
 `ignore_comments` (in)
 :   whether comments should be ignored and treated like whitespace (`#!cpp true`) or yield a parse error
@@ -137,8 +136,6 @@ A UTF-8 byte order mark is silently ignored.
 - Added `ignore_trailing_commas` in version 3.13.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
-- Changed in version 4.0.0 to leave a `#!cpp std::istream` positioned right after the parsed value when `strict` is
-  `#!cpp false`; see [`operator>>`](../operator_gtgt.md#notes).
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/operator_gtgt.md

@@ -33,26 +33,41 @@ A UTF-8 byte order mark is silently ignored.
 Invalid Unicode escapes and unpaired surrogates in the input are reported as
 [`parse_error.101`](../home/exceptions.md#jsonexceptionparse_error101) with a detailed message.
 
-`operator>>` parses exactly one JSON value and leaves the stream positioned right after it, so it can be called
-repeatedly to read a sequence of concatenated JSON values from the same stream:
+`operator>>` parses exactly one JSON value, so it can be called repeatedly to read a sequence of concatenated JSON
+values from the same stream:
 
 ```cpp
-std::istringstream input("1true[2]");
-json j1, j2, j3;
-input >> j1;  // j1 == 1,      stream now positioned right after it
-input >> j2;  // j2 == true
-input >> j3;  // j3 == [2]
+json j1, j2;
+input >> j1;  // parses the first value
+input >> j2;  // parses the next value
 ```
 
-!!! note "Changed behavior for numbers"
+!!! warning "A number must be followed by whitespace"
 
-    A number is the only value whose end can be detected solely by reading the character that follows it. Up to
-    version 3.13.0 that character was consumed and not put back, so the stream was left one byte too far whenever a
-    number was immediately followed by another value: reading `1true` yielded `1` and left the stream at `rue`.
-    Values had to be separated by whitespace to work around this.
+    A number is only terminated by the character that follows it. That character is read from the stream to detect the
+    end of the number, and it is **not** put back. When a value that is a number is immediately followed by the next
+    value, the first character of that next value is lost:
 
-    The terminating character is now only looked at and left in the stream, so no separator is required. Code that
-    relied on the extra byte being swallowed will observe it again.
+    ```cpp
+    std::istringstream input("1true");
+    json j1, j2;
+    input >> j1;  // j1 == 1
+    input >> j2;  // throws parse_error.101: the stream now starts at "rue"
+    ```
+
+    Separating the values with whitespace avoids this, because the character that is eaten is then the separator:
+
+    ```cpp
+    std::istringstream input("1 true");
+    json j1, j2;
+    input >> j1;  // j1 == 1
+    input >> j2;  // j2 == true
+    ```
+
+    Only numbers are affected. Values ending in a self-delimiting character do not read past themselves, so
+    `truefalse`, `[1][2]`, `{"a":1}{"b":2}`, and `"a""b"` can be read back to back without a separator.
+
+    This is tracked in [#5340](https://github.com/nlohmann/json/issues/5340).
 
 Note that reading concatenated values does **not** work for [JSON Lines](../features/parsing/json_lines.md)
 (newline-delimited JSON) input -- see that page for why and for the recommended alternative.
@@ -87,5 +102,3 @@ Note that reading concatenated values does **not** work for [JSON Lines](../feat
 ## Version history
 
 - Added in version 1.0.0.
-- Changed in version 4.0.0 to leave the character that terminates a number in the stream, so that the stream is
-  positioned right after the parsed value for every value type.

include/nlohmann/detail/input/input_adapters.hpp

@@ -101,9 +101,6 @@ class input_stream_adapter
         // maintain ifstream flags, except eof
         if (is != nullptr)
         {
-            // consume the character last returned by get_character() unless it
-            // was given back with release_lookahead()
-            commit_lookahead();
             is->clear(is->rdstate() & std::ios::eofbit);
         }
     }
@@ -118,60 +115,29 @@ class input_stream_adapter
     input_stream_adapter& operator=(input_stream_adapter&&) = delete;
 
     input_stream_adapter(input_stream_adapter&& rhs) noexcept
-        : is(rhs.is), sb(rhs.sb), lookahead(rhs.lookahead)
+        : is(rhs.is), sb(rhs.sb)
     {
         rhs.is = nullptr;
         rhs.sb = nullptr;
-        rhs.lookahead = false;
     }
 
-    // Whether the character last returned by get_character() can be given back
-    // to the input with release_lookahead().
-    static constexpr bool supports_lookahead = true;
-
     // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
     // ensure that std::char_traits<char>::eof() and the character 0xFF do not
     // end up as the same value, e.g., 0xFFFFFFFF.
-    //
-    // The character is peeked rather than consumed: it is only stepped over
-    // once the next character is requested, or when the adapter is destroyed.
-    // Until then, release_lookahead() can leave it in the input.
     std::char_traits<char>::int_type get_character()
     {
-        if (lookahead)
-        {
-            // step over the character returned by the previous call
-            sb->sbumpc();
-        }
-
-        auto res = sb->sgetc();
+        auto res = sb->sbumpc();
         // set eof manually, as we don't use the istream interface.
         if (JSON_HEDLEY_UNLIKELY(res == std::char_traits<char>::eof()))
         {
-            // there is nothing to step over next time
-            lookahead = false;
             is->clear(is->rdstate() | std::ios::eofbit);
         }
-        else
-        {
-            lookahead = true;
-        }
         return res;
     }
 
-    // Leave the character last returned by get_character() in the input, so
-    // that the next read from the stream - by this adapter or by the caller
-    // once parsing is done - sees it again. Unlike putting a consumed
-    // character back, this cannot fail.
-    void release_lookahead() noexcept
-    {
-        lookahead = false;
-    }
-
     template<class T>
     std::size_t get_elements(T* dest, std::size_t count = 1)
     {
-        commit_lookahead();
         auto res = static_cast<std::size_t>(sb->sgetn(reinterpret_cast<char*>(dest), static_cast<std::streamsize>(count * sizeof(T))));
         if (JSON_HEDLEY_UNLIKELY(res < count * sizeof(T)))
         {
@@ -181,23 +147,9 @@ class input_stream_adapter
     }
 
   private:
-    // Step over the character last returned by get_character(). The character
-    // has already been peeked successfully, so for every streambuf with a get
-    // area this is a pointer increment that cannot fail.
-    void commit_lookahead()
-    {
-        if (lookahead)
-        {
-            lookahead = false;
-            sb->sbumpc();
-        }
-    }
-
     /// the associated input stream
     std::istream* is = nullptr;
     std::streambuf* sb = nullptr;
-    /// whether get_character() peeked a character that is not consumed yet
-    bool lookahead = false;
 };
 #endif  // JSON_NO_IO
 

include/nlohmann/detail/input/lexer.hpp

@@ -125,24 +125,6 @@ constexpr bool input_adapter_supports_seek(std::false_type /*detected*/)
     return false;
 }
 
-// Detect whether an input adapter reads with one character of lookahead that
-// can be left in the input (see input_stream_adapter::supports_lookahead),
-// detected like supports_seek above.
-template<typename InputAdapterType>
-using detect_supports_lookahead = decltype(InputAdapterType::supports_lookahead);
-
-template<typename InputAdapterType>
-constexpr bool input_adapter_supports_lookahead(std::true_type /*detected*/)
-{
-    return InputAdapterType::supports_lookahead;
-}
-
-template<typename InputAdapterType>
-constexpr bool input_adapter_supports_lookahead(std::false_type /*detected*/)
-{
-    return false;
-}
-
 /*!
 @brief lexical analysis
 
@@ -164,12 +146,6 @@ class lexer : public lexer_base<BasicJsonType>
     static constexpr bool lazy_token_string =
         input_adapter_supports_seek<InputAdapterType>(is_detected<detect_supports_seek, InputAdapterType> {});
 
-    /// whether a simulated unget can be passed on to the input adapter, which
-    /// then leaves the character in the input; see
-    /// input_adapter_supports_lookahead
-    static constexpr bool can_release_lookahead =
-        input_adapter_supports_lookahead<InputAdapterType>(is_detected<detect_supports_lookahead, InputAdapterType> {});
-
   public:
     using token_type = typename lexer_base<BasicJsonType>::token_type;
 
@@ -1480,21 +1456,6 @@ scan_number_done:
         uncapture_char(std::integral_constant<bool, lazy_token_string> {});
     }
 
-    /// adapter without lookahead: nothing to do (see release_lookahead)
-    void release_lookahead_impl(std::false_type /*can_release*/) const noexcept {}
-
-    /// adapter with lookahead: leave the character in the input instead
-    void release_lookahead_impl(std::true_type /*can_release*/)
-    {
-        if (next_unget)
-        {
-            // the character is read from the input again rather than replayed
-            // from current, so the adapter must not step over it
-            next_unget = false;
-            ia.release_lookahead();
-        }
-    }
-
     /// seekable adapter: nothing was captured, so nothing to undo
     void uncapture_char(std::true_type /*lazy*/) const noexcept {}
 
@@ -1558,29 +1519,6 @@ scan_number_done:
         return position;
     }
 
-    /*!
-    @brief pass a pending simulated unget on to the input
-
-    unget() only rewinds the lexer's own bookkeeping, so the character that
-    terminated the last token (e.g. the character after a number) would still
-    be stepped over when the input adapter is done. Callers that hand the
-    input back to the user afterwards - operator>> and non-strict sax_parse -
-    call this once when scanning is done, so that the input is positioned
-    right after the value.
-
-    Adapters without lookahead (see input_adapter_supports_lookahead) are not
-    handed back to the user, so this is a no-op for them.
-
-    Scanning may continue after this call: @a next_unget is cleared, and the
-    character is read from the input again instead of being replayed from
-    @a current. A pending unget of EOF needs no special case, because reaching
-    EOF leaves no lookahead to release.
-    */
-    void release_lookahead()
-    {
-        release_lookahead_impl(std::integral_constant<bool, can_release_lookahead> {});
-    }
-
     /// seekable adapter: rebuild the last read token from the input on demand
     const std::vector<char_type>& collect_token_chars(std::vector<char_type>& out, std::true_type /*lazy*/) const
     {

include/nlohmann/detail/input/parser.hpp

@@ -99,14 +99,8 @@ class parser
             json_sax_dom_callback_parser<BasicJsonType, InputAdapterType> sdp(result, callback, allow_exceptions, &m_lexer);
             sax_parse_internal(&sdp);
 
-            if (!strict)
-            {
-                // the caller keeps using the input: position it right after
-                // the value by leaving the character that terminated it
-                m_lexer.release_lookahead();
-            }
             // in strict mode, input must be completely read
-            else if (get_token() != token_type::end_of_input)
+            if (strict && (get_token() != token_type::end_of_input))
             {
                 sdp.parse_error(m_lexer.get_position(),
                                 m_lexer.get_token_string(),
@@ -133,13 +127,8 @@ class parser
             json_sax_dom_parser<BasicJsonType, InputAdapterType> sdp(result, allow_exceptions, &m_lexer);
             sax_parse_internal(&sdp);
 
-            if (!strict)
-            {
-                // see above
-                m_lexer.release_lookahead();
-            }
             // in strict mode, input must be completely read
-            else if (get_token() != token_type::end_of_input)
+            if (strict && (get_token() != token_type::end_of_input))
             {
                 sdp.parse_error(m_lexer.get_position(),
                                 m_lexer.get_token_string(),
@@ -176,14 +165,8 @@ class parser
         (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
         const bool result = sax_parse_internal(sax);
 
-        if (result && !strict)
-        {
-            // the caller keeps using the input: position it right after the
-            // value by leaving the character that terminated it
-            m_lexer.release_lookahead();
-        }
         // strict mode: next byte must be EOF
-        else if (result && strict && (get_token() != token_type::end_of_input))
+        if (result && strict && (get_token() != token_type::end_of_input))
         {
             return sax->parse_error(m_lexer.get_position(),
                                     m_lexer.get_token_string(),

include/nlohmann/detail/output/output_adapters.hpp

@@ -13,6 +13,7 @@
 #include <iterator> // back_inserter
 #include <memory> // shared_ptr, make_shared
 #include <string> // basic_string
+#include <utility> // move
 #include <vector> // vector
 
 #ifndef JSON_NO_IO
@@ -118,6 +119,72 @@ class output_string_adapter : public output_adapter_protocol<CharType>
     StringType& str;
 };
 
+/// @brief non-virtual output sink writing into a std::vector
+///
+/// Unlike output_vector_adapter, this sink is not part of the virtual
+/// output_adapter_protocol hierarchy: it is passed to binary_writer by value as
+/// a template parameter, so write_character()/write_characters() are ordinary
+/// (inlinable) calls with no vtable lookup and no shared_ptr. It is used for the
+/// common `to_cbor`/`to_msgpack`/... into a std::vector.
+template<typename CharType, typename AllocatorType = std::allocator<CharType>>
+class output_vector_sink
+{
+  public:
+    explicit output_vector_sink(std::vector<CharType, AllocatorType>& vec) noexcept
+        : v(vec)
+    {}
+
+    void write_character(CharType c)
+    {
+        v.push_back(c);
+    }
+
+    // no JSON_HEDLEY_NON_NULL here: binary_writer legitimately passes a null
+    // pointer with length 0 for empty strings/binary values. Appending an empty
+    // range is a no-op; the type-erased path tolerates this via the (unattributed)
+    // virtual base, and the concrete sink must do the same.
+    void write_characters(const CharType* s, std::size_t length)
+    {
+        v.insert(v.end(), s, s + length);
+    }
+
+  private:
+    std::vector<CharType, AllocatorType>& v;
+};
+
+/// @brief output sink forwarding to a type-erased output adapter
+///
+/// Wraps the polymorphic output_adapter_t so the same binary_writer template can
+/// also target arbitrary adapters (output streams, strings, user-provided
+/// adapters) via the `output_adapter`-based overloads. Each write still goes
+/// through one virtual call, exactly as before; only the concrete sinks above
+/// avoid it.
+template<typename CharType>
+class output_adapter_sink
+{
+  public:
+    explicit output_adapter_sink(output_adapter_t<CharType> adapter)
+        : oa(std::move(adapter))
+    {
+        JSON_ASSERT(oa);
+    }
+
+    void write_character(CharType c)
+    {
+        oa->write_character(c);
+    }
+
+    // no JSON_HEDLEY_NON_NULL: forwards (null, 0) for empty payloads, exactly as
+    // the type-erased path already did before this sink existed
+    void write_characters(const CharType* s, std::size_t length)
+    {
+        oa->write_characters(s, length);
+    }
+
+  private:
+    output_adapter_t<CharType> oa = nullptr;
+};
+
 template<typename CharType, typename StringType = std::basic_string<CharType>>
 class output_adapter
 {

include/nlohmann/json.hpp

@@ -140,7 +140,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     friend ::nlohmann::detail::serializer<basic_json>;
     template<typename BasicJsonType>
     friend class ::nlohmann::detail::iter_impl;
-    template<typename BasicJsonType, typename CharType>
+    template<typename BasicJsonType, typename CharType, typename OutputSinkType>
     friend class ::nlohmann::detail::binary_writer;
     template<typename BasicJsonType, typename InputType, typename SAX>
     friend class ::nlohmann::detail::binary_reader;
@@ -4327,7 +4327,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_cbor(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        to_cbor(j, result);
+        result.reserve(detail::binary_reserve_hint(j));
+        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
+            detail::output_vector_sink<std::uint8_t>(result)).write_cbor(j);
         return result;
     }
 
@@ -4350,7 +4352,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_msgpack(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        to_msgpack(j, result);
+        result.reserve(detail::binary_reserve_hint(j));
+        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
+            detail::output_vector_sink<std::uint8_t>(result)).write_msgpack(j);
         return result;
     }
 
@@ -4375,7 +4379,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             const bool use_type = false)
     {
         std::vector<std::uint8_t> result;
-        to_ubjson(j, result, use_size, use_type);
+        result.reserve(detail::binary_reserve_hint(j));
+        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
+            detail::output_vector_sink<std::uint8_t>(result)).write_ubjson(j, use_size, use_type);
         return result;
     }
 
@@ -4403,7 +4409,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
             const bjdata_version_t version = bjdata_version_t::draft2)
     {
         std::vector<std::uint8_t> result;
-        to_bjdata(j, result, use_size, use_type, version);
+        result.reserve(detail::binary_reserve_hint(j));
+        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
+            detail::output_vector_sink<std::uint8_t>(result)).write_ubjson(j, use_size, use_type, true, true, version);
         return result;
     }
 
@@ -4430,7 +4438,9 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_bson(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        to_bson(j, result);
+        result.reserve(detail::binary_reserve_hint(j));
+        detail::binary_writer<basic_json, std::uint8_t, detail::output_vector_sink<std::uint8_t>>(
+            detail::output_vector_sink<std::uint8_t>(result)).write_bson(j);
         return result;
     }
 

tests/src/unit-deserialization.cpp

@@ -14,15 +14,10 @@ using nlohmann::json;
     using namespace nlohmann::literals; // NOLINT(google-build-using-namespace)
 #endif
 
-#include <cstddef>
 #include <iostream>
 #include <iterator>
 #include <sstream>
-#include <streambuf>
-#include <string>
-#include <utility>
 #include <valarray>
-#include <vector>
 
 #if defined(_WIN32)
     #define NOMINMAX
@@ -224,58 +219,6 @@ class proxy_iterator
     iterator* m_it = nullptr;
 };
 
-// A streambuf that keeps no get area at all and refuses every putback: with an
-// empty get area, sungetc() always ends up in pbackfail(). Used to check that
-// the character terminating a number is left in the input without relying on
-// the streambuf being able to put a consumed character back.
-class no_putback_streambuf : public std::streambuf
-{
-  public:
-    explicit no_putback_streambuf(std::string s) : m_data(std::move(s)) {}
-
-  protected:
-    // peek at the next character without consuming it
-    int_type underflow() override
-    {
-        if (m_pos >= m_data.size())
-        {
-            return traits_type::eof();
-        }
-        return traits_type::to_int_type(m_data[m_pos]);
-    }
-
-    // consume the next character
-    int_type uflow() override
-    {
-        if (m_pos >= m_data.size())
-        {
-            return traits_type::eof();
-        }
-        return traits_type::to_int_type(m_data[m_pos++]);
-    }
-
-    int_type pbackfail(int_type /*c*/) override
-    {
-        return traits_type::eof();
-    }
-
-  private:
-    std::string m_data;
-    std::size_t m_pos = 0;
-};
-
-// read the characters that are left in a stream
-std::string remaining(std::istream& is)
-{
-    std::string result;
-    char c = 0;
-    while (is.get(c))
-    {
-        result += c;
-    }
-    return result;
-}
-
 // JSON_HAS_CPP_20
 #if defined(__cpp_char8_t)
 bool check_utf8()
@@ -1238,122 +1181,6 @@ TEST_CASE("deserialization")
         }
     }
 
-    SECTION("stream position after extraction (#5340)")
-    {
-        SECTION("a number does not consume the character that terminates it")
-        {
-            // a number is only terminated by the character following it; that
-            // character must be given back so the stream is positioned right
-            // after the value
-            const std::vector<std::pair<std::string, std::string>> tests =
-            {
-                {"1true", "true"},
-                {"1[2]", "[2]"},
-                {"1{}", "{}"},
-                {R"(1"a")", R"("a")"},
-                {"1 true", " true"},
-                {"12,", ","},
-                {"-0.5e3x", "x"},
-                {"1null", "null"}
-            };
-
-            for (const auto& test : tests)
-            {
-                CAPTURE(test.first);
-                std::istringstream ss(test.first);
-                json j;
-                ss >> j;
-                CHECK(j == json::parse(test.first.substr(0, test.first.size() - test.second.size())));
-                CHECK(remaining(ss) == test.second);
-            }
-        }
-
-        SECTION("values that are self-delimiting are unaffected")
-        {
-            const std::vector<std::pair<std::string, std::string>> tests =
-            {
-                {"truefalse", "false"},
-                {"[1][2]", "[2]"},
-                {R"({"a":1}{"b":2})", R"({"b":2})"},
-                {R"("a""b")", R"("b")"},
-                {"null null", " null"}
-            };
-
-            for (const auto& test : tests)
-            {
-                CAPTURE(test.first);
-                std::istringstream ss(test.first);
-                json j;
-                ss >> j;
-                CHECK(remaining(ss) == test.second);
-            }
-        }
-
-        SECTION("a number at the end of the input leaves nothing behind")
-        {
-            for (const std::string s :
-                    {"1", "12", "-3.5e2", " 7 "
-                    })
-            {
-                CAPTURE(s);
-                std::istringstream ss(s);
-                json j;
-                ss >> j;
-                CHECK(remaining(ss).find_first_not_of(" \t\n\r") == std::string::npos);
-            }
-        }
-
-        SECTION("repeated extraction of concatenated values")
-        {
-            std::istringstream ss(R"(1true[2]3"x"{"a":4}5)");
-            const std::vector<json> expected =
-            {
-                json(1), json(true), json::parse("[2]"), json(3),
-                json("x"), json::parse(R"({"a":4})"), json(5)
-            };
-
-            for (const auto& e : expected)
-            {
-                json j;
-                ss >> j;
-                CHECK(j == e);
-            }
-        }
-
-        SECTION("sax_parse with strict == false")
-        {
-            std::istringstream ss("1true");
-            SaxEventLogger l;
-            CHECK(json::sax_parse(ss, &l, nlohmann::detail::input_format_t::json, false));
-            CHECK(l.events.size() == 1);
-            CHECK(l.events[0] == "number_unsigned(1)");
-            CHECK(remaining(ss) == "true");
-        }
-
-        SECTION("strict parsing still rejects trailing data")
-        {
-            std::istringstream ss("1true");
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::parse(ss),
-                                 "[json.exception.parse_error.101] parse error at line 1, column 5: syntax error while parsing value - unexpected true literal; expected end of input", json::parse_error&);
-
-            std::istringstream ss2("1true");
-            CHECK_FALSE(json::accept(ss2));
-        }
-
-        SECTION("a streambuf that cannot put back is not needed")
-        {
-            // the terminating character is never consumed, so no putback
-            // position is required
-            no_putback_streambuf buf("1true");
-            std::istream is(&buf);
-            json j;
-            is >> j;
-            CHECK(j == json(1));
-            CHECK(remaining(is) == "true");
-        }
-    }
-
     // build with C++20
     // JSON_HAS_CPP_20
 #if defined(__cpp_char8_t)