<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 3083: What should ios::iword(-1) do?</title>
<meta property="og:title" content="Issue 3083: What should ios::iword(-1) do?">
<meta property="og:description" content="C++ library issue. Status: C++20">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue3083.html">
<meta property="og:type" content="website">
<meta property="og:image" content="http://cplusplus.github.io/LWG/images/cpp_logo.png">
<meta property="og:image:alt" content="C++ logo">
<style>
  p {text-align:justify}
  li {text-align:justify}
  pre code.backtick::before { content: "`" }
  pre code.backtick::after { content: "`" }
  blockquote.note
  {
    background-color:#E0E0E0;
    padding-left: 15px;
    padding-right: 15px;
    padding-top: 1px;
    padding-bottom: 1px;
  }
  ins {background-color:#A0FFA0}
  del {background-color:#FFA0A0}
  table.issues-index { border: 1px solid; border-collapse: collapse; }
  table.issues-index th { text-align: center; padding: 4px; border: 1px solid; }
  table.issues-index td { padding: 4px; border: 1px solid; }
  table.issues-index td:nth-child(1) { text-align: right; }
  table.issues-index td:nth-child(2) { text-align: left; }
  table.issues-index td:nth-child(3) { text-align: left; }
  table.issues-index td:nth-child(4) { text-align: left; }
  table.issues-index td:nth-child(5) { text-align: center; }
  table.issues-index td:nth-child(6) { text-align: center; }
  table.issues-index td:nth-child(7) { text-align: left; }
  table.issues-index td:nth-child(5) span.no-pr { color: red; }
  @media (prefers-color-scheme: dark) {
     html {
        color: #ddd;
        background-color: black;
     }
     ins {
        background-color: #225522
     }
     del {
        background-color: #662222
     }
     a {
        color: #6af
     }
     a:visited {
        color: #6af
     }
     blockquote.note
     {
        background-color: rgba(255, 255, 255, .10)
     }
  }
</style>
</head>
<body>
<hr>
<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#C++20">C++20</a> status.</em></p>
<h3 id="3083"><a href="lwg-defects.html#3083">3083</a>. What should <code>ios::iword(-1)</code> do?</h3>
<p><b>Section:</b> 31.5.2.6 <a href="https://wg21.link/ios.base.storage">[ios.base.storage]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2018-03-16 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#ios.base.storage">issues</a> in [ios.base.storage].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Is calling <code>iword</code> and <code>pword</code> with a negative argument undefined, or should it cause 
a failure condition (and return a valid reference)? What about <code>INT_MAX</code>? What about <code>0</code>?
<p/>
Using arbitrary indices isn't safe, because the implementation could be already using them for 
something else. Some replies on the reflector suggested the only reliable argument is one obtained from 
<code>ios_base::xalloc()</code>. Others pointed out that the iwords and pwords could be stored in sparse 
arrays, so that any value from <code>INT_MIN</code> to <code>INT_MAX</code> could be a valid key (which might 
require the implementation to use keys outside that range for its own entries in the arrays).
<p/>
If it's undefined we should add a <i>Requires</i> element to the spec. If invalid indices are supposed 
to cause a failure we need to define which indices are invalid (and ensure that's something the 
implementation can check), and specify that it causes a failure.
</p>

<p><i>[
2018-03-27 Moved to Tentatively Ready after 5 positive votes on c++std-lib.
]</i></p>


<p><i>[2018-06 Rapperswil: Adopted]</i></p>



<p id="res-3083"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4727">N4727</a>.
</p>

<ol>
<li>
<p>Edit 31.5.2.6 <a href="https://wg21.link/ios.base.storage">[ios.base.storage]</a> as indicated:</p>
<blockquote>
<pre>
long&amp; iword(int idx);
</pre>
<blockquote>
<p>
<ins>-?- <i>Requires:</i> <code>idx</code> is a value obtained by a call to <code>xalloc</code>.</ins>
<p/>
-3- <i>Effects:</i> If <code>iarray</code> is a null pointer, [&hellip;]
<p/>
[&hellip;]
</p>
</blockquote>
<pre>
void*&amp; pword(int idx);
</pre>
<blockquote>
<p>
<ins>-?- <i>Requires:</i> <code>idx</code> is a value obtained by a call to <code>xalloc</code>.</ins>
<p/>
-5- <i>Effects:</i> If <code>iarray</code> is a null pointer, [&hellip;]
<p/>
[&hellip;]
</p>
</blockquote>
</blockquote>
</li>
</ol>





</body>
</html>
