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<title>Issue 531: array forms of unformatted input functions</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#CD1">CD1</a> status.</em></p>
<h3 id="531"><a href="lwg-defects.html#531">531</a>. array forms of unformatted input functions</h3>
<p><b>Section:</b> 31.7.5.4 <a href="https://wg21.link/istream.unformatted">[istream.unformatted]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2005-11-23 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#istream.unformatted">issues</a> in [istream.unformatted].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The array forms of unformatted input functions don't seem to have well-defined
semantics for zero-element arrays in a couple of cases. The affected ones
(<code>istream::get()</code> and <code>istream::getline()</code>) are supposed to
terminate when <code>(n - 1)</code> characters are stored, which obviously can
never be true when <code>(n == 0)</code> holds to start with. See
c++std-lib-16071.
</p>


<p id="res-531"><b>Proposed resolution:</b></p>
<p>
I suggest changing 27.6.1.3, p7 (<code>istream::get()</code>), bullet 1 to read:
</p>
            <ul>
                <li>
                    <code>(n &lt; 1)</code> is true or <code>(n - 1)</code> characters
                    are stored;
                </li>
            </ul>
<p>
Change 27.6.1.3, p9:
</p>

<blockquote><p>
If the function stores no characters, it calls <code>setstate(failbit)</code> (which
may throw <code>ios_base::failure</code> (27.4.4.3)).  In any case, <ins>if <code>(n
&gt; 0)</code> is true</ins> it then stores a null character into the next
successive location of the array.
</p></blockquote>

        <p>

and similarly p17 (<code>istream::getline()</code>), bullet 3 to:

        </p>
            <ul>
                <li>
                    <code>(n &lt; 1)</code> is true or <code>(n - 1)</code> characters
                    are stored (in which case the function calls
                    <code>setstate(failbit)</code>).
                </li>
            </ul>

        <p>

In addition, to clarify that <code>istream::getline()</code> must not store the
terminating NUL character unless the the array has non-zero size, Robert
Klarer suggests in c++std-lib-16082 to change 27.6.1.3, p20 to read:

        </p>
            <blockquote><p>

In any case, provided <code>(n &gt; 0)</code> is true, it then stores a null character
(using charT()) into the next successive location of the array.

            </p></blockquote>

<p><i>[
post-Redmond:  Pete noticed that the current resolution for <code>get</code> requires
writing to out of bounds memory when <code>n == 0</code>.  Martin provided fix.
]</i></p>







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