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4276.front() and back() are not hardened for zero-length std::arrays
Section: 23.3.3.5 [array.zero] Status: New Submitter: Jan Schultke Opened: 2025-06-08 Last modified: 2025-06-14
Priority: Not Prioritized
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Discussion:
The intent of P3471 "Standard library hardening" is clearly to provide hardened preconditions for members of sequence containers, including std::array. However, a zero-length std::array dodges this hardening by having undefined behavior for front() and back() explicitly specified in 23.3.3.5 [array.zero] paragraph 3.
front() and back() would be hardened as well, as specified in 23.2.4 [sequence.reqmts].
Proposed resolution:
This wording is relative to N5008.
Modify 23.3.3.5 [array.zero] as indicated:
-3- The effect of calling
front()orback()for a zero-sized array is undefined.
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