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211. operator>>(istream&, string&) doesn't set failbit

Section: 20.3.3.9 [string.io] Status: TC1 Submitter: Scott Snyder Opened: 2000-02-04 Last modified: 2016-12-23

Priority: Not Prioritized

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Discussion:

The description of the stream extraction operator for std::string (section 21.3.7.9 [lib.string.io]) does not contain a requirement that failbit be set in the case that the operator fails to extract any characters from the input stream.

This implies that the typical construction

std::istream is;
std::string str;
...
while (is >> str) ... ;

(which tests failbit) is not required to terminate at EOF.

Furthermore, this is inconsistent with other extraction operators, which do include this requirement. (See sections 27.7.4.2 [istream.formatted] and 27.7.4.3 [istream.unformatted]), where this requirement is present, either explicitly or implicitly, for the extraction operators. It is also present explicitly in the description of getline (istream&, string&, charT) in section 20.3.3.9 [string.io] paragraph 8.)

Proposed resolution:

Insert new paragraph after paragraph 2 in section 20.3.3.9 [string.io]:

If the function extracts no characters, it calls is.setstate(ios::failbit) which may throw ios_base::failure (27.4.4.3).