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Fix GCC narrowing warning and address review feedback

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- get_bytes(): replace `len -= static_cast<NumberType>(wanted)` with an
  explicit `len = static_cast<NumberType>(len - ...)`. The compound
  assignment promoted the operands to int and narrowed back, which GCC
  rejects under -Werror=arith-conversion when NumberType is narrower than
  int (e.g. UBJSON's int16 length). This also fixes the CodeQL build.
- get_bytes(): add JSON_ASSERT(read == wanted) documenting that
  get_elements() never returns more than requested (per review).
- iterator_input_adapter: de-duplicate the iterator_is_contiguous
  definition with the #if inside the initializer (per review).
- Add a comment explaining why the memcpy source is &*current (needed for
  non-pointer contiguous iterators), and drop the redundant parentheses.
- Run astyle on the new unit test so the amalgamation/format check passes.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Niels Lohmann
2026-07-04 08:57:45 +02:00
co-authored by Claude Opus 4.8
parent 9eee7a7b9b
commit 282ff6ce5c
4 changed files with 26 additions and 16 deletions
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single_include/nlohmann/json.hpp
+11 -6
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@@ -7023,11 +7023,11 @@ class iterator_input_adapter
// whether IteratorType refers to a contiguous range and therefore supports
// a std::memcpy fast path (pointers always do; in C++20 we can also detect
// library iterators such as those of std::vector and std::string)
static constexpr bool iterator_is_contiguous =
#if defined(__cpp_lib_concepts) && defined(JSON_HAS_CPP_20)
static constexpr bool iterator_is_contiguous = std::is_pointer<IteratorType>::value || std::contiguous_iterator<IteratorType>;
#else
static constexpr bool iterator_is_contiguous = std::is_pointer<IteratorType>::value;
std::contiguous_iterator<IteratorType> ||
#endif
std::is_pointer<IteratorType>::value;
// contiguous fast path: bulk copy the remaining range with std::memcpy
template<class T>
@@ -7038,7 +7038,9 @@ class iterator_input_adapter
const std::size_t copied = (std::min)(wanted, available);
if (JSON_HEDLEY_LIKELY(copied != 0))
{
std::memcpy(dest, &(*current), copied);
// &*current yields the raw address for both raw pointers and
// non-pointer contiguous iterators (e.g. std::vector's iterator)
std::memcpy(dest, &*current, copied);
std::advance(current, static_cast<typename std::iterator_traits<IteratorType>::difference_type>(copied / sizeof(char_type)));
}
return copied;
@@ -13174,13 +13176,16 @@ class binary_reader
if (JSON_HEDLEY_UNLIKELY(read < wanted))
{
// premature end of input: shrink to what was actually read and
// report the failure at the first missing byte
// report the failure at the first missing byte (same position
// accounting as get_to() for partial number reads)
result.resize(old_size + read);
++chars_read;
current = char_traits<char_type>::eof();
return unexpect_eof(format, context);
}
len -= static_cast<NumberType>(wanted);
// a full chunk was read; get_elements() never returns more than requested
JSON_ASSERT(read == wanted);
len = static_cast<NumberType>(len - static_cast<NumberType>(wanted));
}
return true;
}