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2600. ios_base must store inaccessible iostate flags

Section: 31.5.2.6 [ios.base.storage] Status: NAD Submitter: David Krauss Opened: 2016-03-14 Last modified: 2019-02-26

Priority: Not Prioritized

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Discussion:

DR 41⁽ⁱ⁾, "Ios_base needs clear(), exceptions()" stopped short of providing the interface suggested in its title, but it did require the underlying state to be stored in ios_base. Because rdstate() is also missing, ios_base manipulators relying on iword and pword cannot detect failure. The only safe alternative is to manipulate a derived class, which must be a template.

libc++ already provides the interface as a nonconforming extension. libstdc++ implements the internal state but leaves it frustratingly inaccessible, as specified. Any conforming implementation should be able to provide the interface without ABI problems.

[2016-04, Issues Telecon]

This is really a request for an (feature) API. Passing to LEWG.

[LEWG Kona 2017]

Recommend NAD: iostreams aren't used in this way enough to spend committee time on it. However, a paper could change our minds.

Proposed resolution: