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### 199. What does `allocate(0)` return?

Section: 16.4.4.6 [allocator.requirements] Status: TC1 Submitter: Matt Austern Opened: 1999-11-19 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

Suppose that `A` is a class that conforms to the Allocator requirements of Table 32, and `a` is an object of class `A` What should be the return value of `a.allocate(0)`? Three reasonable possibilities: forbid the argument `0`, return a null pointer, or require that the return value be a unique non-null pointer.

Proposed resolution:

Add a note to the `allocate` row of Table 32: "[Note: If `n == 0`, the return value is unspecified. --end note]"

Rationale:

A key to understanding this issue is that the ultimate use of allocate() is to construct an iterator, and that iterator for zero length sequences must be the container's past-the-end representation. Since this already implies special case code, it would be over-specification to mandate the return value.