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69. Must elements of a vector be contiguous?

Section: 23.3.13[vector]Status:TC1Submitter: Andrew KoenigOpened: 1998-07-29Last modified: 2016-01-28

Priority:Not Prioritized

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Discussion:

The issue is this: Must the elements of a vector be in contiguous memory?

(Please note that this is entirely separate from the question ofwhether a vector iterator is required to be a pointer; the answer tothat question is clearly "no," as it would rule outdebugging implementations)

Proposed resolution:

Add the following text to the end of 23.3.13[vector],paragraph 1.

The elements of a vector are stored contiguously, meaning that if v is avector<T, Allocator> where T is some type other thanbool, then it obeys the identity&v[n] == &v[0] + n for all0 <= n < v.size().

Rationale:

The LWG feels that as a practical matter the answer is clearly"yes". There was considerable discussion as to the best wayto express the concept of "contiguous", which is notdirectly defined in the standard. Discussion included:

• An operational definition similar to the above proposed resolution is already used for valarray (29.6.2.4[valarray.access]).
• There is no need to explicitly consider a user-defined operator& because elements must be copyconstructible (23.2[container.requirements] para 3) and copyconstructible (16.4.4.2[utility.arg.requirements]) specifies requirements for operator&.
• There is no issue of one-past-the-end because of language rules.