This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of Tentatively Ready status.

4276. front() and back() are not hardened for zero-length std::arrays

Section: 23.3.3.5 [array.zero] Status: Tentatively Ready Submitter: Jan Schultke Opened: 2025-06-08 Last modified: 2025-08-26

Priority: Not Prioritized

View other active issues in [array.zero].

View all other issues in [array.zero].

View all issues with Tentatively Ready status.

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.

Without this paragraph, front() and back() would be hardened as well, as specified in 23.2.4 [sequence.reqmts].

[2025-08-21; Reflector poll]

Set status to Tentatively Ready after eight votes in favour during reflector poll.

Proposed resolution:

This wording is relative to N5008.

1. Modify 23.3.3.5 [array.zero] as indicated:

   -3- The effect of calling front() or back() for a zero-sized array is undefined.