3199. istream >> bitset<0> fails

Section: 22.9.4 [bitset.operators] Status: C++20 Submitter: Davis Herring Opened: 2019-04-05 Last modified: 2021-02-25

Priority: Not Prioritized

View all other issues in [bitset.operators].

View all issues with C++20 status.

Discussion:

From a StackOverflow question:

[bitset.operators]/5.1 says that extracting a bitset<0> stops after reading 0 characters. /6 then says that, since no characters were stored, failbit is set.

[2019-06-09; Priority to 0 and Status to Tentatively Ready after five positive votes on the reflector.]

Proposed resolution:

This wording is relative to N4810.

  1. Modify 22.9.4 [bitset.operators] as indicated:

    template<class charT, class traits, size_t N>
  basic_istream<charT, traits>&
    operator>>(basic_istream<charT, traits>& is, bitset<N>& x);

    […]

    -6- If N > 0 and no characters are stored in str, calls is.setstate(ios_base::failbit) (which may throw ios_base::failure (31.5.4.4 [iostate.flags])).