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397. ostream::sentry dtor throws exceptions

Section: 31.7.6.2.4 [ostream.sentry] Status: NAD Editorial Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2021-06-06

Priority: Not Prioritized

View all other issues in [ostream.sentry].

View all issues with NAD Editorial status.

Discussion:

17.4.4.8, p3 prohibits library dtors from throwing exceptions.

27.6.2.3, p4 says this about the ostream::sentry dtor: 

    -4- If ((os.flags() & ios_base::unitbuf) && !uncaught_exception())
        is true, calls os.flush().

27.6.2.6, p7 that describes ostream::flush() says: 

    -7- If rdbuf() is not a null pointer, calls rdbuf()->pubsync().
        If that function returns ?-1 calls setstate(badbit) (which
        may throw ios_base::failure (27.4.4.3)).

That seems like a defect, since both pubsync() and setstate() can throw an exception.

[ The contradiction is real. Clause 17 says destructors may never throw exceptions, and clause 27 specifies a destructor that does throw. In principle we might change either one. We're leaning toward changing clause 17: putting in an "unless otherwise specified" clause, and then putting in a footnote saying the sentry destructor is the only one that can throw. PJP suggests specifying that sentry::~sentry() should internally catch any exceptions it might cause. ]

[ See 418(i) and 622(i) for related issues. ]

[ 2009-07 Frankfurt ]

Move to Review. Add "Throws: nothing" to the specification of ostream::sentry::~sentry().

[ 2009-10-13 Daniel adds: ]

The proposed resolution of 835(i) is written to match the outcome of this issue.

[ 2009 Santa Cruz: ]

Move to Open. Our intent is to solve this issue with 835(i).

[ 2010-03-06 Martin updates wording. ]

[ 2010 Pittsburgh: ]

Moved to NAD Editorial.

Rationale:

Solved by 835(i).

Proposed resolution:

Add after [ostream::sentry] p17: 

~sentry();

-17- If (os.flags() & ios_base::unitbuf) is true, calls os.flush().

Throws: Nothing.