<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Issue 393: do_in/do_out operation on state unclear</title>
<meta property="og:title" content="Issue 393: do_in/do_out operation on state unclear">
<meta property="og:description" content="C++ library issue. Status: NAD Editorial">
<meta property="og:url" content="https://cplusplus.github.io/LWG/issue393.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#NAD_Editorial">NAD Editorial</a> status.</em></p>
<h3 id="393"><a href="lwg-closed.html#393">393</a>. do_in/do_out operation on state unclear</h3>
<p><b>Section:</b> 28.3.4.2.5.3 <a href="https://wg21.link/locale.codecvt.virtuals">[locale.codecvt.virtuals]</a> <b>Status:</b> <a href="lwg-active.html#NAD_Editorial">NAD Editorial</a>
 <b>Submitter:</b> Alberto Barbati <b>Opened:</b> 2002-12-24 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#locale.codecvt.virtuals">active issues</a> in [locale.codecvt.virtuals].</p>
<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt.virtuals">issues</a> in [locale.codecvt.virtuals].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p>
<p><b>Discussion:</b></p>
<p>
this DR follows the discussion on the previous thread "codecvt::do_in
not consuming external characters". It's just a clarification issue
and not a request for a change.
</p>
<p>
Can do_in()/do_out() produce output characters without consuming input 
characters as a result of operation on state?
</p>


<p id="res-393"><b>Proposed resolution:</b></p>
<p>
Add a note at the end of 28.3.4.2.5.3 <a href="https://wg21.link/locale.codecvt.virtuals">[locale.codecvt.virtuals]</a>, 
paragraph 3:
</p>

<p>
[Note: As a result of operations on state, it can return ok or partial 
and set from_next == from and to_next != to. --end note]
</p>


<p><b>Rationale:</b></p>
<p>
The submitter believes that standard already provides an affirmative
answer to the question. However, the current wording has induced a few
library implementors to make the incorrect assumption that
do_in()/do_out() always consume at least one internal character when
they succeed.
</p>

<p>
The submitter also believes that the proposed resolution is not in
conflict with the related issue 76. Moreover, by explicitly allowing
operations on state to produce characters, a codecvt implementation
may effectively implement N-to-M translations without violating the
"one character at a time" principle described in such issue. On a side
note, the footnote in the proposed resolution of issue 76 that
informally rules out N-to-M translations for basic_filebuf should be
removed if this issue is accepted as valid.
</p>


<p><i>[
Kona (2007): The proposed resolution is to add a note. Since this is
non-normative, the issue is editorial, but we believe that the note is
correct. Proposed Disposition: NAD, Editorial
]</i></p>






</body>
</html>
