From: Martin Sebor <sebor@roguewave.com>
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Date: Tue, 05 Feb 2008 18:42:06 -0700
Organization: Rogue Wave Software, Inc.
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Subject: ambiguity in [istream.iterator]
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To: C++ libraries mailing list
Message c++std-lib-20221

The description of how an istream_iterator object becomes an
end-of-stream iterator is a) ambiguous and b) out of date WRT
issue 468:

   istream_iterator reads (using operator>>) successive elements
   from the input stream for which it was constructed. After it
   is constructed, and every time ++ is used, the iterator reads
   and stores a value of T. If the end of stream is reached
   (operator void*() on the stream returns false), the iterator
   becomes equal to the end-of-stream iterator value.

istream::operator void*() returns null if istream::fail() is true,
otherwise non-null. istream::fail() returns true if failbit or
badbit is set in rdstate(). Reaching the end of stream doesn't
necessarily imply that failbit or badbit is set (e.g., after
extracting an int from stringstream("123") the stream object will
have reached the end of stream but fail() is false and operator
void*() will return a non-null value).

Proposed fix:

   An object of type istream_iterator extracts (using operator>>)
   successive elements from the input stream for which it was
   constructed. After it is constructed, and every time operator++
   is called, the object extracts and stores a value of type T. If
   the end of stream is reached (calling eof() on the associated
   stream returns true), the object becomes the end-of-stream
   iterator.

Issue 468:
http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#468