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### 664. `do_unshift` for `codecvt<char, char, mbstate_t>`

Section: 28.4.2.5.3 [locale.codecvt.virtuals] Status: CD1 Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

28.4.2.5.3 [locale.codecvt.virtuals], para 7 says (regarding `do_unshift`):

> Effects: Places characters starting at to that should be appended to terminate a sequence when the current `stateT` is given by `state`.237) Stores no more than `(to_limit - to)` destination elements, and leaves the `to_next` pointer pointing one beyond the last element successfully stored. `codecvt<char, char, mbstate_t>` stores no characters.

The following objection has been raised:

> Since the C++ Standard permits a nontrivial conversion for the required instantiations of `codecvt`, it is overly restrictive to say that `do_unshift` must store no characters and return `noconv`.

[Plum ref _222152Y50]

Proposed resolution:

Change 28.4.2.5.3 [locale.codecvt.virtuals], p7:

> Effects: Places characters starting at to that should be appended to terminate a sequence when the current `stateT` is given by state.237) Stores no more than (to_limit -to) destination elements, and leaves the to_next pointer pointing one beyond the last element successfully stored. `codecvt<char, char, mbstate_t>` stores no characters.