<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 352: missing fpos requirements</title>
<meta property="og:title" content="Issue 352: missing fpos requirements">
<meta property="og:description" content="C++ library issue. Status: CD1">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue352.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#CD1">CD1</a> status.</em></p>
<h3 id="352"><a href="lwg-defects.html#352">352</a>. missing fpos requirements</h3>
<p><b>Section:</b> 27.2.3 <a href="https://wg21.link/char.traits.typedefs">[char.traits.typedefs]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2001-12-02 <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#char.traits.typedefs">issues</a> in [char.traits.typedefs].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<i>(1)</i>
There are no requirements on the <code>stateT</code> template parameter of
<code>fpos</code> listed in 27.4.3. The interface appears to require that
the type be at least Assignable and CopyConstructible (27.4.3.1, p1),
and I think also DefaultConstructible (to implement the operations in
Table 88).
</p>
<p>
21.1.2, p3, however, only requires that
<code>char_traits&lt;charT&gt;::state_type</code> meet the requirements of
CopyConstructible types.
</p>
<p>
<i>(2)</i>
Additionally, the <code>stateT</code> template argument has no
corresponding typedef in fpos which might make it difficult to use in
generic code.
</p>


<p id="res-352"><b>Proposed resolution:</b></p>
<p>
Modify 21.1.2, p4 from
</p>
<p>
    Requires: <code>state_type</code> shall meet the requirements of
              CopyConstructible types (20.1.3).
</p>
<p>
    Requires: state_type shall meet the requirements of Assignable
              (23.1, p4), CopyConstructible (20.1.3), and
              DefaultConstructible  (20.1.4) types.
</p>



<p><b>Rationale:</b></p>
<p>The LWG feels this is two issues, as indicated above. The first is
a defect---std::basic_fstream is unimplementable without these
additional requirements---and the proposed resolution fixes it.  The
second is questionable; who would use that typedef?  The class
template fpos is used only in a very few places, all of which know the
state type already.  Unless motivation is provided, the second should
be considered NAD.</p>





</body>
</html>
