<vector>: Avoid off-by-default warning C4365 in vector<bool> copy algorithms with /J
#6013
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…char` (when treated as unsigned under `/J`).
…on`. Add lots of `static_cast<ptrdiff_t>` and a few `static_cast<size_t>`. prefix.lst is what adds `/w14365`. Cleanup: Avoid unnecessary `next()`.
davidmrdavid
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Jan 15, 2026
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LGTM, but will re-approve if/when this is applied: 655e813#r2695480146
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@davidmrdavid I've pushed a commit to use |
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Reported by a major customer.
Our policy is that we attempt to be
/W4clean but not/Wallclean, as/Wallcontains a large number of extremely noisy warnings, many of which aren't suitable for using in production (some are intended for focused investigations, or were added for one unusual scenario, or were just way noisier than their value proved to be).However, we generally do attempt to keep the codebase clean with respect to the off-by-default warning C4365, as we build our tests with
/w14365:STL/tests/std/tests/prefix.lst
Line 6 in 4634ad4
Under the extremely obscure compiler option
/J,charis treated as an unsigned type. This triggers C4365 signed/unsigned mismatch warnings when assigning promotedinttocharin thevector<bool>optimization forcopy()implemented by #3353 (merged 2023-09-21, shipped in MSVC Build Tools 14.39 / VS 2022 17.9).Avoiding those warnings is easy, so even though
/Jis rarely used, and we don't officially support being C4365 clean, we may as well silence them and add test coverage.Enabling the test coverage is significantly more obnoxious but all of the issues were in the test itself and are avoidable with repetitive casts.