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### 352. missing fpos requirements

Section: 23.2.3 [char.traits.typedefs] Status: CD1 Submitter: Martin Sebor Opened: 2001-12-02 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

(1) There are no requirements on the `stateT` template parameter of `fpos` listed in 27.4.3. The interface appears to require that the type be at least Assignable and CopyConstructible (27.4.3.1, p1), and I think also DefaultConstructible (to implement the operations in Table 88).

21.1.2, p3, however, only requires that `char_traits<charT>::state_type` meet the requirements of CopyConstructible types.

(2) Additionally, the `stateT` template argument has no corresponding typedef in fpos which might make it difficult to use in generic code.

Proposed resolution:

Modify 21.1.2, p4 from

Requires: `state_type` shall meet the requirements of CopyConstructible types (20.1.3).

Requires: state_type shall meet the requirements of Assignable (23.1, p4), CopyConstructible (20.1.3), and DefaultConstructible (20.1.4) types.

Rationale:

The LWG feels this is two issues, as indicated above. The first is a defect---std::basic_fstream is unimplementable without these additional requirements---and the proposed resolution fixes it. The second is questionable; who would use that typedef? The class template fpos is used only in a very few places, all of which know the state type already. Unless motivation is provided, the second should be considered NAD.