<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang xml:lang>
<head>
  <meta charset="utf-8" />
  <meta name="generator" content="mpark/wg21" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
  <meta name="dcterms.date" content="2023-05-15" />
  <title>Native handles and file streams</title>
  <style>
      code{white-space: pre-wrap;}
      span.smallcaps{font-variant: small-caps;}
      span.underline{text-decoration: underline;}
      div.column{display: inline-block; vertical-align: top; width: 50%;}
      div.csl-block{margin-left: 1.5em;}
      ul.task-list{list-style: none;}
      pre > code.sourceCode { white-space: pre; position: relative; }
      pre > code.sourceCode > span { display: inline-block; line-height: 1.25; }
      pre > code.sourceCode > span:empty { height: 1.2em; }
      .sourceCode { overflow: visible; }
      code.sourceCode > span { color: inherit; text-decoration: inherit; }
      div.sourceCode { margin: 1em 0; }
      pre.sourceCode { margin: 0; }
      @media screen {
      div.sourceCode { overflow: auto; }
      }
      @media print {
      pre > code.sourceCode { white-space: pre-wrap; }
      pre > code.sourceCode > span { text-indent: -5em; padding-left: 5em; }
      }
      pre.numberSource code
        { counter-reset: source-line 0; }
      pre.numberSource code > span
        { position: relative; left: -4em; counter-increment: source-line; }
      pre.numberSource code > span > a:first-child::before
        { content: counter(source-line);
          position: relative; left: -1em; text-align: right; vertical-align: baseline;
          border: none; display: inline-block;
          -webkit-touch-callout: none; -webkit-user-select: none;
          -khtml-user-select: none; -moz-user-select: none;
          -ms-user-select: none; user-select: none;
          padding: 0 4px; width: 4em;
          color: #aaaaaa;
        }
      pre.numberSource { margin-left: 3em; border-left: 1px solid #aaaaaa;  padding-left: 4px; }
      div.sourceCode
        {  background-color: #f6f8fa; }
      @media screen {
      pre > code.sourceCode > span > a:first-child::before { text-decoration: underline; }
      }
      code span { } /* Normal */
      code span.al { color: #ff0000; } /* Alert */
      code span.an { } /* Annotation */
      code span.at { } /* Attribute */
      code span.bn { color: #9f6807; } /* BaseN */
      code span.bu { color: #9f6807; } /* BuiltIn */
      code span.cf { color: #00607c; } /* ControlFlow */
      code span.ch { color: #9f6807; } /* Char */
      code span.cn { } /* Constant */
      code span.co { color: #008000; font-style: italic; } /* Comment */
      code span.cv { color: #008000; font-style: italic; } /* CommentVar */
      code span.do { color: #008000; } /* Documentation */
      code span.dt { color: #00607c; } /* DataType */
      code span.dv { color: #9f6807; } /* DecVal */
      code span.er { color: #ff0000; font-weight: bold; } /* Error */
      code span.ex { } /* Extension */
      code span.fl { color: #9f6807; } /* Float */
      code span.fu { } /* Function */
      code span.im { } /* Import */
      code span.in { color: #008000; } /* Information */
      code span.kw { color: #00607c; } /* Keyword */
      code span.op { color: #af1915; } /* Operator */
      code span.ot { } /* Other */
      code span.pp { color: #6f4e37; } /* Preprocessor */
      code span.re { } /* RegionMarker */
      code span.sc { color: #9f6807; } /* SpecialChar */
      code span.ss { color: #9f6807; } /* SpecialString */
      code span.st { color: #9f6807; } /* String */
      code span.va { } /* Variable */
      code span.vs { color: #9f6807; } /* VerbatimString */
      code span.wa { color: #008000; font-weight: bold; } /* Warning */
      code.diff {color: #898887}
      code.diff span.va {color: #006e28}
      code.diff span.st {color: #bf0303}
  </style>
  <style type="text/css">
body {
margin: 5em;
font-family: serif;

hyphens: auto;
line-height: 1.35;
text-align: justify;
}
@media screen and (max-width: 30em) {
body {
margin: 1.5em;
}
}
div.wrapper {
max-width: 60em;
margin: auto;
}
ul {
list-style-type: none;
padding-left: 2em;
margin-top: -0.2em;
margin-bottom: -0.2em;
}
a {
text-decoration: none;
color: #4183C4;
}
a.hidden_link {
text-decoration: none;
color: inherit;
}
li {
margin-top: 0.6em;
margin-bottom: 0.6em;
}
h1, h2, h3, h4 {
position: relative;
line-height: 1;
}
a.self-link {
position: absolute;
top: 0;
left: calc(-1 * (3.5rem - 26px));
width: calc(3.5rem - 26px);
height: 2em;
text-align: center;
border: none;
transition: opacity .2s;
opacity: .5;
font-family: sans-serif;
font-weight: normal;
font-size: 83%;
}
a.self-link:hover { opacity: 1; }
a.self-link::before { content: "§"; }
ul > li:before {
content: "\2014";
position: absolute;
margin-left: -1.5em;
}
:target { background-color: #C9FBC9; }
:target .codeblock { background-color: #C9FBC9; }
:target ul { background-color: #C9FBC9; }
.abbr_ref { float: right; }
.folded_abbr_ref { float: right; }
:target .folded_abbr_ref { display: none; }
:target .unfolded_abbr_ref { float: right; display: inherit; }
.unfolded_abbr_ref { display: none; }
.secnum { display: inline-block; min-width: 35pt; }
.header-section-number { display: inline-block; min-width: 35pt; }
.annexnum { display: block; }
div.sourceLinkParent {
float: right;
}
a.sourceLink {
position: absolute;
opacity: 0;
margin-left: 10pt;
}
a.sourceLink:hover {
opacity: 1;
}
a.itemDeclLink {
position: absolute;
font-size: 75%;
text-align: right;
width: 5em;
opacity: 0;
}
a.itemDeclLink:hover { opacity: 1; }
span.marginalizedparent {
position: relative;
left: -5em;
}
li span.marginalizedparent { left: -7em; }
li ul > li span.marginalizedparent { left: -9em; }
li ul > li ul > li span.marginalizedparent { left: -11em; }
li ul > li ul > li ul > li span.marginalizedparent { left: -13em; }
div.footnoteNumberParent {
position: relative;
left: -4.7em;
}
a.marginalized {
position: absolute;
font-size: 75%;
text-align: right;
width: 5em;
}
a.enumerated_item_num {
position: relative;
left: -3.5em;
display: inline-block;
margin-right: -3em;
text-align: right;
width: 3em;
}
div.para { margin-bottom: 0.6em; margin-top: 0.6em; text-align: justify; }
div.section { text-align: justify; }
div.sentence { display: inline; }
span.indexparent {
display: inline;
position: relative;
float: right;
right: -1em;
}
a.index {
position: absolute;
display: none;
}
a.index:before { content: "⟵"; }

a.index:target {
display: inline;
}
.indexitems {
margin-left: 2em;
text-indent: -2em;
}
div.itemdescr {
margin-left: 3em;
}
.bnf {
font-family: serif;
margin-left: 40pt;
margin-top: 0.5em;
margin-bottom: 0.5em;
}
.ncbnf {
font-family: serif;
margin-top: 0.5em;
margin-bottom: 0.5em;
margin-left: 40pt;
}
.ncsimplebnf {
font-family: serif;
font-style: italic;
margin-top: 0.5em;
margin-bottom: 0.5em;
margin-left: 40pt;
background: inherit; 
}
span.textnormal {
font-style: normal;
font-family: serif;
white-space: normal;
display: inline-block;
}
span.rlap {
display: inline-block;
width: 0px;
}
span.descr { font-style: normal; font-family: serif; }
span.grammarterm { font-style: italic; }
span.term { font-style: italic; }
span.terminal { font-family: monospace; font-style: normal; }
span.nonterminal { font-style: italic; }
span.tcode { font-family: monospace; font-style: normal; }
span.textbf { font-weight: bold; }
span.textsc { font-variant: small-caps; }
a.nontermdef { font-style: italic; font-family: serif; }
span.emph { font-style: italic; }
span.techterm { font-style: italic; }
span.mathit { font-style: italic; }
span.mathsf { font-family: sans-serif; }
span.mathrm { font-family: serif; font-style: normal; }
span.textrm { font-family: serif; }
span.textsl { font-style: italic; }
span.mathtt { font-family: monospace; font-style: normal; }
span.mbox { font-family: serif; font-style: normal; }
span.ungap { display: inline-block; width: 2pt; }
span.textit { font-style: italic; }
span.texttt { font-family: monospace; }
span.tcode_in_codeblock { font-family: monospace; font-style: normal; }
span.phantom { color: white; }

span.math { font-style: normal; }
span.mathblock {
display: block;
margin-left: auto;
margin-right: auto;
margin-top: 1.2em;
margin-bottom: 1.2em;
text-align: center;
}
span.mathalpha {
font-style: italic;
}
span.synopsis {
font-weight: bold;
margin-top: 0.5em;
display: block;
}
span.definition {
font-weight: bold;
display: block;
}
.codeblock {
margin-left: 1.2em;
line-height: 127%;
}
.outputblock {
margin-left: 1.2em;
line-height: 127%;
}
div.itemdecl {
margin-top: 2ex;
}
code.itemdeclcode {
white-space: pre;
display: block;
}
span.textsuperscript {
vertical-align: super;
font-size: smaller;
line-height: 0;
}
.footnotenum { vertical-align: super; font-size: smaller; line-height: 0; }
.footnote {
font-size: small;
margin-left: 2em;
margin-right: 2em;
margin-top: 0.6em;
margin-bottom: 0.6em;
}
div.minipage {
display: inline-block;
margin-right: 3em;
}
div.numberedTable {
text-align: center;
margin: 2em;
}
div.figure {
text-align: center;
margin: 2em;
}
table {
border: 1px solid black;
border-collapse: collapse;
margin-left: auto;
margin-right: auto;
margin-top: 0.8em;
text-align: left;
hyphens: none; 
}
td, th {
padding-left: 1em;
padding-right: 1em;
vertical-align: top;
}
td.empty {
padding: 0px;
padding-left: 1px;
}
td.left {
text-align: left;
}
td.right {
text-align: right;
}
td.center {
text-align: center;
}
td.justify {
text-align: justify;
}
td.border {
border-left: 1px solid black;
}
tr.rowsep, td.cline {
border-top: 1px solid black;
}
tr.even, tr.odd {
border-bottom: 1px solid black;
}
tr.capsep {
border-top: 3px solid black;
border-top-style: double;
}
tr.header {
border-bottom: 3px solid black;
border-bottom-style: double;
}
th {
border-bottom: 1px solid black;
}
span.centry {
font-weight: bold;
}
div.table {
display: block;
margin-left: auto;
margin-right: auto;
text-align: center;
width: 90%;
}
span.indented {
display: block;
margin-left: 2em;
margin-bottom: 1em;
margin-top: 1em;
}
ol.enumeratea { list-style-type: none; background: inherit; }
ol.enumerate { list-style-type: none; background: inherit; }

code.sourceCode > span { display: inline; }
</style>
  <link href="data:image/x-icon;base64,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" rel="icon" />
  
  <!--[if lt IE 9]>
    <script src="//cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv-printshiv.min.js"></script>
  <![endif]-->
</head>
<body>
<div class="wrapper">
<header id="title-block-header">
<h1 class="title" style="text-align:center">Native handles and file
streams</h1>
<table style="border:none;float:right">
  <tr>
    <td>Document #:</td>
    <td>P1759R6</td>
  </tr>
  <tr>
    <td>Date:</td>
    <td>2023-05-15</td>
  </tr>
  <tr>
    <td style="vertical-align:top">Project:</td>
    <td>Programming Language C++</td>
  </tr>
  <tr>
    <td style="vertical-align:top">Audience:</td>
    <td>
      Library<br>
    </td>
  </tr>
  <tr>
    <td style="vertical-align:top">Reply-to:</td>
    <td>
      Elias Kosunen<br>&lt;<a href="mailto:isocpp@eliaskosunen.com" class="email">isocpp@eliaskosunen.com</a>&gt;<br>
    </td>
  </tr>
</table>
</header>
<div style="clear:both">
<div id="TOC" role="doc-toc">
<h1 id="toctitle">Contents</h1>
<ul>
<li><a href="#abstract" id="toc-abstract"><span class="toc-section-number">1</span> Abstract<span></span></a></li>
<li><a href="#history" id="toc-history"><span class="toc-section-number">2</span> Revision
History<span></span></a></li>
<li><a href="#motivation" id="toc-motivation"><span class="toc-section-number">3</span> Motivation<span></span></a></li>
<li><a href="#scope" id="toc-scope"><span class="toc-section-number">4</span> Scope<span></span></a></li>
<li><a href="#design" id="toc-design"><span class="toc-section-number">5</span> Design
Discussion<span></span></a></li>
<li><a href="#implementation" id="toc-implementation"><span class="toc-section-number">6</span> Implementation<span></span></a></li>
<li><a href="#specification" id="toc-specification"><span class="toc-section-number">7</span> Technical
Specifications<span></span></a></li>
<li><a href="#acknowledgements" id="toc-acknowledgements"><span class="toc-section-number">8</span>
Acknowledgements<span></span></a></li>
<li><a href="#bibliography" id="toc-bibliography"><span class="toc-section-number">9</span> References<span></span></a></li>
</ul>
</div>
<h1 data-number="1" id="abstract"><span class="header-section-number">1</span> Abstract<a href="#abstract" class="self-link"></a></h1>
<p>This paper proposes adding a new typedef to standard file streams:
<code class="sourceCode default">native_handle_type</code>. This type is
an alias to whatever type the platform uses for its file descriptors:
<code class="sourceCode default">int</code> on POSIX,
<code class="sourceCode default">HANDLE</code>
(<code class="sourceCode default">void*</code>) on Windows, and
something else on other platforms. This type is a non-owning handle and
has generally sane semantics: default constructability and trivial
copyability.</p>
<p>Alongside this, this paper proposes adding a concrete member
function: <code class="sourceCode default">.native_handle()</code>,
returning a <code class="sourceCode default">native_handle_type</code>,
to the following class templates:</p>
<ul>
<li><code class="sourceCode default">basic_filebuf</code></li>
<li><code class="sourceCode default">basic_ifstream</code></li>
<li><code class="sourceCode default">basic_ofstream</code></li>
<li><code class="sourceCode default">basic_fstream</code></li>
</ul>
<h1 data-number="2" id="history"><span class="header-section-number">2</span> Revision History<a href="#history" class="self-link"></a></h1>
<h2 data-number="2.1" id="r6"><span class="header-section-number">2.1</span> R6<a href="#r6" class="self-link"></a></h2>
<ul>
<li>Update wording per LWG feedback
<ul>
<li>Make <code class="sourceCode default">native_handle()</code>
<code class="sourceCode default">const</code> and
<code class="sourceCode default">noexcept</code></li>
<li>Add explicit <code class="sourceCode default">#define</code> for
feature test macro, and specify, that it should also appear in
<code class="sourceCode default">&lt;fstream&gt;</code></li>
<li>Do not require
<code class="sourceCode default">native_handle_type</code> to be
standard-layout</li>
<li><em>Returns</em> -&gt; <em>Effects</em></li>
<li>Other minor changes</li>
</ul></li>
</ul>
<h2 data-number="2.2" id="r5"><span class="header-section-number">2.2</span> R5<a href="#r5" class="self-link"></a></h2>
<ul>
<li>Update design discussion
<ul>
<li>Add <code class="sourceCode default">std::stacktrace_handle</code>
as a type that has a
<code class="sourceCode default">.native_handle()</code>, and
comparisons to it</li>
</ul></li>
<li>Update wording:
<ul>
<li>Update wording to reference <span class="citation" data-cites="N4928">[<a href="#ref-N4928" role="doc-biblioref">N4928</a>]</span></li>
<li><em>Expects</em> -&gt; <em>Preconditions</em></li>
<li>Other minor changes based on LEWG feedback</li>
</ul></li>
</ul>
<h2 data-number="2.3" id="r4"><span class="header-section-number">2.3</span> R4<a href="#r4" class="self-link"></a></h2>
<ul>
<li>Update wording:
<ul>
<li><code class="sourceCode default">native_handle_type</code> constexpr
default constructor -&gt; default constructor</li>
<li>Add wording as to how the handle returned by
<code class="sourceCode default">.native_handle()</code> is valid only
when the file is open</li>
</ul></li>
<li>Update wording to reference the latest standard draft <span class="citation" data-cites="N4892">[<a href="#ref-N4892" role="doc-biblioref">N4892</a>]</span></li>
</ul>
<h2 data-number="2.4" id="r3"><span class="header-section-number">2.4</span> R3<a href="#r3" class="self-link"></a></h2>
<ul>
<li>Add <code class="sourceCode default">std::condition_variable</code>
and <span class="citation" data-cites="P2146">[<a href="#ref-P2146" role="doc-biblioref">P2146R2</a>]</span> to list of standard types
having a <code class="sourceCode default">.native_handle()</code> member
function</li>
<li>Update wording to reference the latest standard draft <span class="citation" data-cites="N4849">[<a href="#ref-N4849" role="doc-biblioref">N4849</a>]</span>, and update references to other
P-numbered papers</li>
<li>Change paper title</li>
</ul>
<h2 data-number="2.5" id="r2"><span class="header-section-number">2.5</span> R2<a href="#r2" class="self-link"></a></h2>
<ul>
<li>Minor touches to wording
<ul>
<li>Refine requirements on
<code class="sourceCode default">native_handle_type</code> (remove
<code class="sourceCode default">equality_comparable</code>, add
constexpr default constructability)</li>
<li>Fix some broken references using section numbers in the WD</li>
<li>Update reference to the WD</li>
</ul></li>
<li>Editorial fixes</li>
</ul>
<h2 data-number="2.6" id="r1"><span class="header-section-number">2.6</span> R1<a href="#r1" class="self-link"></a></h2>
<ul>
<li>Make <code class="sourceCode default">native_handle_type</code> be
standard layout</li>
<li>Add precondition
(<code class="sourceCode default">is_open() == true</code>) to
<code class="sourceCode default">.native_handle()</code></li>
<li>Add feature test macro
<code class="sourceCode default">__cpp_lib_fstream_native_handle</code></li>
<li>Fix errors with opening the file with POSIX APIs in Motivation (see,
we need this paper, fstreams are easier to open correctly!)</li>
<li>Add additional motivating use case in vectored/scatter-gather
IO</li>
<li><code class="sourceCode default">Regular</code> -&gt;
<code class="sourceCode default">regular</code></li>
</ul>
<p>Incorporate LEWGI feedback from Cologne (July 2019):</p>
<ul>
<li>Move to a member function and member typedef</li>
<li>Make <code class="sourceCode default">native_handle</code> return
value not be mandated to be unique</li>
<li>Add note about how the presence of the members is required, and not
implementation-defined (like for thread)</li>
</ul>
<h2 data-number="2.7" id="r0"><span class="header-section-number">2.7</span> R0<a href="#r0" class="self-link"></a></h2>
<p>Initial revision.</p>
<h1 data-number="3" id="motivation"><span class="header-section-number">3</span> Motivation<a href="#motivation" class="self-link"></a></h1>
<p>For some operations, using OS/platform-specific file APIs is
necessary. If a user wanted to use these APIs, they’re unable to use
iostreams without reopening the file.</p>
<p>For example, if one wanted to query the time a file was last modified
on POSIX, one would use <code class="sourceCode default">fstat</code>,
which takes a file descriptor:</p>
<div class="sourceCode" id="cb1"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="dt">int</span> fd <span class="op">=</span> <span class="op">::</span>open<span class="op">(</span><span class="st">&quot;~/foo.txt&quot;</span>, O_RDONLY<span class="op">)</span>;</span>
<span id="cb1-2"><a href="#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="op">::</span>stat s<span class="op">{}</span>;</span>
<span id="cb1-3"><a href="#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="dt">int</span> err <span class="op">=</span> <span class="op">::</span>fstat<span class="op">(</span>fd, <span class="op">&amp;</span>s<span class="op">)</span>;</span>
<span id="cb1-4"><a href="#cb1-4" aria-hidden="true" tabindex="-1"></a>std<span class="op">::</span>chrono<span class="op">::</span>sys_seconds last_modified <span class="op">=</span> std<span class="op">::</span>chrono<span class="op">::</span>seconds<span class="op">(</span>s<span class="op">.</span>st_mtime<span class="op">.</span>tv_sec<span class="op">)</span>;</span></code></pre></div>
<p>The Filesystem TS introduced the
<code class="sourceCode default">status</code> function returning a
<code class="sourceCode default">file_status</code> structure. This
doesn’t solve our problem, because
<code class="sourceCode default">std::filesystem::status</code> takes a
path, not a native file descriptor. Using paths is generally discouraged
in these sort of situations, because the path may not refer to the same
file it referred to previously (the file might’ve been moved), or the
file might not exist anymore at all. In short, using paths is
potentially racy.</p>
<p>Also,
<code class="sourceCode default">std::filesystem::file_status</code>
only contains member functions
<code class="sourceCode default">type()</code> and
<code class="sourceCode default">permissions()</code>, not one for last
time of modification. Extending this structure is out of scope for this
proposal, and not feasible for every single possible operation the user
may wish to do with OS APIs, of which querying simple file properties is
but a small subset.</p>
<p>If the user needs to do a single operation not supported by the
standard library, they have to make a choice between using OS APIs
exclusively, or reopening the file every time it’s necessary. The former
is unfortunate from the persective of the standard library and its
usefulness. The latter is likely to lead to forgetting to close the
file, or running into buffering or synchronization issues, as is the
case with C APIs.</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co">// Writing the latest modification date to a file</span></span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a>std<span class="op">::</span>chrono<span class="op">::</span>sys_seconds last_modified<span class="op">(</span><span class="dt">int</span> fd<span class="op">)</span> <span class="op">{</span></span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a>    <span class="co">// See above for POSIX implementation using fstat</span></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a><span class="co">// Today&#39;s code</span></span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true" tabindex="-1"></a><span class="co">// Option #1:</span></span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true" tabindex="-1"></a><span class="co">// Use iostreams by reopening the file</span></span>
<span id="cb2-10"><a href="#cb2-10" aria-hidden="true" tabindex="-1"></a><span class="op">{</span></span>
<span id="cb2-11"><a href="#cb2-11" aria-hidden="true" tabindex="-1"></a>    <span class="dt">int</span> fd <span class="op">=</span> <span class="op">::</span>open<span class="op">(</span><span class="st">&quot;~/foo.txt&quot;</span>, O_RDONLY<span class="op">)</span>; <span class="co">// CreateFile on Windows</span></span>
<span id="cb2-12"><a href="#cb2-12" aria-hidden="true" tabindex="-1"></a>    <span class="kw">auto</span> lm <span class="op">=</span> last_modified<span class="op">(</span>fd<span class="op">)</span>;</span>
<span id="cb2-13"><a href="#cb2-13" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-14"><a href="#cb2-14" aria-hidden="true" tabindex="-1"></a>    <span class="op">::</span>close<span class="op">(</span>fd<span class="op">)</span>; <span class="co">// CloseFile on Windows</span></span>
<span id="cb2-15"><a href="#cb2-15" aria-hidden="true" tabindex="-1"></a>    <span class="co">// Hope the path still points to the file!</span></span>
<span id="cb2-16"><a href="#cb2-16" aria-hidden="true" tabindex="-1"></a>    <span class="co">// Need to allocate </span></span>
<span id="cb2-17"><a href="#cb2-17" aria-hidden="true" tabindex="-1"></a>    std<span class="op">::</span>ofstream of<span class="op">(</span><span class="st">&quot;~/foo.txt&quot;</span><span class="op">)</span>;</span>
<span id="cb2-18"><a href="#cb2-18" aria-hidden="true" tabindex="-1"></a>    of <span class="op">&lt;&lt;</span> std<span class="op">::</span>chrono<span class="op">::</span>format<span class="op">(</span><span class="st">&quot;</span><span class="sc">%c</span><span class="st">&quot;</span>, lm<span class="op">)</span> <span class="op">&lt;&lt;</span> <span class="ch">&#39;</span><span class="sc">\n</span><span class="ch">&#39;</span>;</span>
<span id="cb2-19"><a href="#cb2-19" aria-hidden="true" tabindex="-1"></a>    <span class="co">// Need to flush</span></span>
<span id="cb2-20"><a href="#cb2-20" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
<span id="cb2-21"><a href="#cb2-21" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-22"><a href="#cb2-22" aria-hidden="true" tabindex="-1"></a><span class="co">// Option #2:</span></span>
<span id="cb2-23"><a href="#cb2-23" aria-hidden="true" tabindex="-1"></a><span class="co">// Abstain from using iostreams altogether</span></span>
<span id="cb2-24"><a href="#cb2-24" aria-hidden="true" tabindex="-1"></a><span class="op">{</span></span>
<span id="cb2-25"><a href="#cb2-25" aria-hidden="true" tabindex="-1"></a>    <span class="dt">int</span> fd <span class="op">=</span> <span class="op">::</span>open<span class="op">(</span><span class="st">&quot;~/foo.txt&quot;</span>, O_RDWR<span class="op">)</span>;</span>
<span id="cb2-26"><a href="#cb2-26" aria-hidden="true" tabindex="-1"></a>    <span class="kw">auto</span> lm <span class="op">=</span> last_modified<span class="op">(</span>fd<span class="op">)</span>;</span>
<span id="cb2-27"><a href="#cb2-27" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-28"><a href="#cb2-28" aria-hidden="true" tabindex="-1"></a>    <span class="co">// Using ::write() is clunky;</span></span>
<span id="cb2-29"><a href="#cb2-29" aria-hidden="true" tabindex="-1"></a>    <span class="co">// skipping error handling for brevity</span></span>
<span id="cb2-30"><a href="#cb2-30" aria-hidden="true" tabindex="-1"></a>    <span class="kw">auto</span> str <span class="op">=</span> std<span class="op">::</span>chrono<span class="op">::</span>format<span class="op">(</span><span class="st">&quot;</span><span class="sc">%c\n</span><span class="st">&quot;</span>, lm<span class="op">)</span>;</span>
<span id="cb2-31"><a href="#cb2-31" aria-hidden="true" tabindex="-1"></a>    <span class="op">::</span>write<span class="op">(</span>fd, str<span class="op">.</span>data<span class="op">()</span>, str<span class="op">.</span>size<span class="op">())</span>;</span>
<span id="cb2-32"><a href="#cb2-32" aria-hidden="true" tabindex="-1"></a>    <span class="co">// Remember to close!</span></span>
<span id="cb2-33"><a href="#cb2-33" aria-hidden="true" tabindex="-1"></a>    <span class="co">// Hope format or push_back doesn&#39;t throw</span></span>
<span id="cb2-34"><a href="#cb2-34" aria-hidden="true" tabindex="-1"></a>    <span class="op">::</span>close<span class="op">(</span>fd<span class="op">)</span>;</span>
<span id="cb2-35"><a href="#cb2-35" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span>
<span id="cb2-36"><a href="#cb2-36" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-37"><a href="#cb2-37" aria-hidden="true" tabindex="-1"></a><span class="co">// This proposal</span></span>
<span id="cb2-38"><a href="#cb2-38" aria-hidden="true" tabindex="-1"></a><span class="co">// No need to use platform-specific APIs to open the file</span></span>
<span id="cb2-39"><a href="#cb2-39" aria-hidden="true" tabindex="-1"></a><span class="op">{</span></span>
<span id="cb2-40"><a href="#cb2-40" aria-hidden="true" tabindex="-1"></a>    std<span class="op">::</span>ofstream of<span class="op">(</span><span class="st">&quot;~/foo.txt&quot;</span><span class="op">)</span>;</span>
<span id="cb2-41"><a href="#cb2-41" aria-hidden="true" tabindex="-1"></a>    <span class="kw">auto</span> lm <span class="op">=</span> last_modified<span class="op">(</span>of<span class="op">.</span>native_handle<span class="op">())</span>;</span>
<span id="cb2-42"><a href="#cb2-42" aria-hidden="true" tabindex="-1"></a>    of <span class="op">&lt;&lt;</span> std<span class="op">::</span>chrono<span class="op">::</span>format<span class="op">(</span><span class="st">&quot;</span><span class="sc">%c</span><span class="st">&quot;</span>, lm<span class="op">)</span> <span class="op">&lt;&lt;</span> <span class="ch">&#39;</span><span class="sc">\n</span><span class="ch">&#39;</span>;</span>
<span id="cb2-43"><a href="#cb2-43" aria-hidden="true" tabindex="-1"></a>    <span class="co">// RAII does ownership handling for us</span></span>
<span id="cb2-44"><a href="#cb2-44" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<p>The utility of getting a file descriptor (or other native file
handle) is not limited to getting the last modification date. Other
examples include, but are definitely not limited to:</p>
<ul>
<li>file locking (<code class="sourceCode default">fcntl()</code> +
<code class="sourceCode default">F_SETLK</code> on POSIX,
<code class="sourceCode default">LockFile</code> on Windows)</li>
<li>getting file status flags
(<code class="sourceCode default">fcntl()</code> +
<code class="sourceCode default">F_GETFL</code> on POSIX,
<code class="sourceCode default">GetFileInformationByHandle</code> on
Windows)</li>
<li>vectored/scatter-gather IO
(<code class="sourceCode default">vread()</code>/<code class="sourceCode default">vwrite()</code>
on POSIX)</li>
<li>non-blocking IO (<code class="sourceCode default">fcntl()</code> +
<code class="sourceCode default">O_NONBLOCK</code>/<code class="sourceCode default">F_SETSIG</code>
on POSIX)</li>
</ul>
<p>Basically, this paper would make standard file streams interoperable
with operating system interfaces, making iostreams more useful in that
regard.</p>
<p>An alternative would be adding a lot of this functionality to
<code class="sourceCode default">fstream</code> and
<code class="sourceCode default">filesystem</code>. The problem is, that
some of this behavior is inherently platform-specific. For example,
getting the inode of a file is something that only makes sense on POSIX,
so cannot be made part of the
<code class="sourceCode default">fstream</code> interface, and should
only accessible through the native file descriptor.</p>
<p>With <span class="citation" data-cites="P1031">[<a href="#ref-P1031" role="doc-biblioref">P1031R2</a>]</span> and <span class="citation" data-cites="P2146">[<a href="#ref-P2146" role="doc-biblioref">P2146R2</a>]</span>, we’re potentially getting a
replacement for iostreams in the standard, or at least facilities
complementing them. The author thinks, that even if these papers were to
be merged to the standard, the functionality described in this paper
would still be useful, as iostreams aren’t going anywhere soon.</p>
<h1 data-number="4" id="scope"><span class="header-section-number">4</span> Scope<a href="#scope" class="self-link"></a></h1>
<p>This paper does <em>not</em> propose enabling the construction of a
file stream or a file stream buffer from a native file handle. The
author is worried of ownership and implementation issues possibly
associated with this design.</p>
<div class="sourceCode" id="cb3"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="co">// NOT PROPOSED</span></span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a><span class="pp">#include </span><span class="im">&lt;fstream&gt;</span></span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="pp">#include </span><span class="im">&lt;fcntl.h&gt;</span></span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a><span class="kw">auto</span> fd <span class="op">=</span> <span class="op">::</span>open<span class="op">(</span><span class="co">/* ... */</span><span class="op">)</span>;</span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true" tabindex="-1"></a><span class="kw">auto</span> f <span class="op">=</span> std<span class="op">::</span>fstream<span class="op">{</span>fd<span class="op">}</span>;</span></code></pre></div>
<p>This paper also does <em>not</em> touch anything related to
<code class="sourceCode default">FILE*</code>, namely getting a native
handle out of one.</p>
<h1 data-number="5" id="design"><span class="header-section-number">5</span> Design Discussion<a href="#design" class="self-link"></a></h1>
<h2 data-number="5.1" id="impl-defined"><span class="header-section-number">5.1</span> Implementation-definedness of
native handles and presence of them<a href="#impl-defined" class="self-link"></a></h2>
<p>The wording related to native handles in <span>33.2.3
<a href="https://wg21.link/thread.req.native">[thread.req.native]</a></span>
is as follows:</p>
<blockquote>
<p>Several classes described in this Clause have members
<code class="sourceCode default">native_handle_type</code> and
<code class="sourceCode default">native_handle</code>. The presence of
these members and their semantics is implementation-defined. [
<em>Note:</em> These members allow implementations to provide access to
implementation details. Their names are specified to facilitate portable
compile-time detection. Actual use of these members is inherently
non-portable. — <em>end note</em> ]</p>
</blockquote>
<p>In more plain terms, the presence of native handles in
<code class="sourceCode default">std::thread</code>,
<code class="sourceCode default">std::mutex</code>, and
<code class="sourceCode default">std::condition_variable</code>, is
implementation-defined, without a way to query, whether they are
provided (except with SFINAE magic). This design is deemed bad by the
author and by LEWG, so this paper aims to not do that again.</p>
<p>The wording related to native handles in <span>19.6.3.3
<a href="https://wg21.link/stacktrace.entry.obs">[stacktrace.entry.obs]</a></span>
is as follows:</p>
<blockquote>
<p>The semantics of this function are implementation-defined.</p>
<p><em>Remarks:</em> Successive invocations of the
<code class="sourceCode default">native_handle</code> function for an
unchanged <code class="sourceCode default">stacktrace_entry</code>
object return identical values.</p>
</blockquote>
<p>While this design is a huge step up compared to threads, the author
would like to have more strict normative guarantees for this
facility.</p>
<p>This paper proposes to:</p>
<ul>
<li>set requirements for
<code class="sourceCode default">native_handle_type</code>:
<code class="sourceCode default">semiregular</code>ity, trivial
copyability</li>
<li>define (semi-normatively), what a <em>native handle</em> for a file
means, and how it behaves</li>
</ul>
<h1 data-number="6" id="implementation"><span class="header-section-number">6</span> Implementation<a href="#implementation" class="self-link"></a></h1>
<p>Implementing this paper should be a relatively trivial task.</p>
<p>Although all implementations surveyed (libstdc++, libc++ and MSVC)
use <code class="sourceCode default">FILE*</code> instead of native file
descriptors in their
<code class="sourceCode default">basic_filebuf</code> implementations,
these platforms provide facilites to get a native handle from a
<code class="sourceCode default">FILE*</code>;
<code class="sourceCode default">fileno</code> on POSIX, and
<code class="sourceCode default">_fileno</code> +
<code class="sourceCode default">_get_osfhandle</code> on Windows. The
following reference implementations use these.</p>
<p>For libstdc++ on Linux:</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="kw">template</span> <span class="op">&lt;</span><span class="kw">class</span> CharT, <span class="kw">class</span> Traits<span class="op">&gt;</span></span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> basic_filebuf <span class="op">:</span> <span class="kw">public</span> basic_streambuf<span class="op">&lt;</span>CharT, Traits<span class="op">&gt;</span> <span class="op">{</span></span>
<span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb4-4"><a href="#cb4-4" aria-hidden="true" tabindex="-1"></a>    <span class="kw">using</span> native_handle_type <span class="op">=</span> <span class="dt">int</span>;</span>
<span id="cb4-5"><a href="#cb4-5" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb4-6"><a href="#cb4-6" aria-hidden="true" tabindex="-1"></a>    native_handle_type native_handle<span class="op">()</span> <span class="op">{</span></span>
<span id="cb4-7"><a href="#cb4-7" aria-hidden="true" tabindex="-1"></a>        <span class="ot">assert</span><span class="op">(</span>is_open<span class="op">())</span>;</span>
<span id="cb4-8"><a href="#cb4-8" aria-hidden="true" tabindex="-1"></a>        <span class="co">// _M_file (__basic_file&lt;char&gt;) has a member function for this purpose</span></span>
<span id="cb4-9"><a href="#cb4-9" aria-hidden="true" tabindex="-1"></a>        <span class="cf">return</span> _M_file<span class="op">.</span>fd<span class="op">()</span>;</span>
<span id="cb4-10"><a href="#cb4-10" aria-hidden="true" tabindex="-1"></a>        <span class="co">// ::fileno(_M_file.file()) could also be used</span></span>
<span id="cb4-11"><a href="#cb4-11" aria-hidden="true" tabindex="-1"></a>    <span class="op">}</span></span>
<span id="cb4-12"><a href="#cb4-12" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb4-13"><a href="#cb4-13" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<p>For libc++ on Linux:</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="kw">template</span> <span class="op">&lt;</span><span class="kw">class</span> CharT, <span class="kw">class</span> Traits<span class="op">&gt;</span></span>
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> basic_filebuf <span class="op">:</span> <span class="kw">public</span> basic_streambuf<span class="op">&lt;</span>CharT, Traits<span class="op">&gt;</span> <span class="op">{</span></span>
<span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a>    <span class="kw">using</span> native_handle_type <span class="op">=</span> <span class="dt">int</span>;</span>
<span id="cb5-5"><a href="#cb5-5" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb5-6"><a href="#cb5-6" aria-hidden="true" tabindex="-1"></a>    native_handle_type native_handle<span class="op">()</span> <span class="op">{</span></span>
<span id="cb5-7"><a href="#cb5-7" aria-hidden="true" tabindex="-1"></a>        <span class="ot">assert</span><span class="op">(</span>is_open<span class="op">())</span>;</span>
<span id="cb5-8"><a href="#cb5-8" aria-hidden="true" tabindex="-1"></a>        <span class="co">// __file_ is a FILE*</span></span>
<span id="cb5-9"><a href="#cb5-9" aria-hidden="true" tabindex="-1"></a>        <span class="cf">return</span> <span class="op">::</span>fileno<span class="op">(</span>__file_<span class="op">)</span></span>
<span id="cb5-10"><a href="#cb5-10" aria-hidden="true" tabindex="-1"></a>    <span class="op">}</span></span>
<span id="cb5-11"><a href="#cb5-11" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb5-12"><a href="#cb5-12" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<p>For MSVC:</p>
<div class="sourceCode" id="cb6"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a><span class="kw">template</span> <span class="op">&lt;</span><span class="kw">class</span> CharT, <span class="kw">class</span> Traits<span class="op">&gt;</span></span>
<span id="cb6-2"><a href="#cb6-2" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> basic_filebuf <span class="op">:</span> <span class="kw">public</span> basic_streambuf<span class="op">&lt;</span>CharT, Traits<span class="op">&gt;</span> <span class="op">{</span></span>
<span id="cb6-3"><a href="#cb6-3" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb6-4"><a href="#cb6-4" aria-hidden="true" tabindex="-1"></a>    <span class="kw">using</span> native_handle_type <span class="op">=</span> HANDLE;</span>
<span id="cb6-5"><a href="#cb6-5" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb6-6"><a href="#cb6-6" aria-hidden="true" tabindex="-1"></a>    native_handle_type native_handle<span class="op">()</span> <span class="op">{</span></span>
<span id="cb6-7"><a href="#cb6-7" aria-hidden="true" tabindex="-1"></a>        <span class="ot">assert</span><span class="op">(</span>is_open<span class="op">())</span>;</span>
<span id="cb6-8"><a href="#cb6-8" aria-hidden="true" tabindex="-1"></a>        <span class="co">// _Myfile is a FILE*</span></span>
<span id="cb6-9"><a href="#cb6-9" aria-hidden="true" tabindex="-1"></a>        <span class="kw">auto</span> cfile <span class="op">=</span> <span class="op">::</span>_fileno<span class="op">(</span>_Myfile<span class="op">)</span>;</span>
<span id="cb6-10"><a href="#cb6-10" aria-hidden="true" tabindex="-1"></a>        <span class="co">// _get_osfhandle returns intptr_t, which can be cast to HANDLE (void*)</span></span>
<span id="cb6-11"><a href="#cb6-11" aria-hidden="true" tabindex="-1"></a>        <span class="cf">return</span> <span class="kw">static_cast</span><span class="op">&lt;</span>HANDLE<span class="op">&gt;(::</span>_get_osfhandle<span class="op">(</span>cfile<span class="op">))</span>;</span>
<span id="cb6-12"><a href="#cb6-12" aria-hidden="true" tabindex="-1"></a>    <span class="op">}</span></span>
<span id="cb6-13"><a href="#cb6-13" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb6-14"><a href="#cb6-14" aria-hidden="true" tabindex="-1"></a><span class="op">}</span></span></code></pre></div>
<p>For all of these cases, implementing
<code class="sourceCode default">.native_handle()</code> for
<code class="sourceCode default">ifstream</code>,
<code class="sourceCode default">ofstream</code> and
<code class="sourceCode default">fstream</code> is trivial:</p>
<div class="sourceCode" id="cb7"><pre class="sourceCode cpp"><code class="sourceCode cpp"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="kw">template</span> <span class="op">&lt;</span><span class="kw">class</span> CharT, <span class="kw">class</span> Traits<span class="op">&gt;</span></span>
<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a><span class="kw">class</span> basic_ifstream <span class="op">:</span> <span class="kw">public</span> basic_istream<span class="op">&lt;</span>CharT, Traits<span class="op">&gt;</span> <span class="op">{</span></span>
<span id="cb7-3"><a href="#cb7-3" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb7-4"><a href="#cb7-4" aria-hidden="true" tabindex="-1"></a>    <span class="kw">using</span> native_handle_type <span class="op">=</span></span>
<span id="cb7-5"><a href="#cb7-5" aria-hidden="true" tabindex="-1"></a>        <span class="kw">typename</span> basic_filebuf<span class="op">&lt;</span>CharT, Traits<span class="op">&gt;::</span>native_handle_type;</span>
<span id="cb7-6"><a href="#cb7-6" aria-hidden="true" tabindex="-1"></a>    <span class="co">// ...</span></span>
<span id="cb7-7"><a href="#cb7-7" aria-hidden="true" tabindex="-1"></a>    native_handle_type native_handle<span class="op">()</span> <span class="op">{</span></span>
<span id="cb7-8"><a href="#cb7-8" aria-hidden="true" tabindex="-1"></a>        <span class="cf">return</span> rdbuf<span class="op">()-&gt;</span>native_handle<span class="op">()</span>;</span>
<span id="cb7-9"><a href="#cb7-9" aria-hidden="true" tabindex="-1"></a>    <span class="op">}</span></span>
<span id="cb7-10"><a href="#cb7-10" aria-hidden="true" tabindex="-1"></a><span class="op">}</span>;</span>
<span id="cb7-11"><a href="#cb7-11" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb7-12"><a href="#cb7-12" aria-hidden="true" tabindex="-1"></a><span class="co">// Repeat for ofstream and fstream</span></span></code></pre></div>
<h1 data-number="7" id="specification"><span class="header-section-number">7</span> Technical Specifications<a href="#specification" class="self-link"></a></h1>
<p>The wording is based on <span class="citation" data-cites="N4928">[<a href="#ref-N4928" role="doc-biblioref">N4928</a>]</span>.</p>
<p><em>Note to editor:</em> In the wording below, replace the character
� with the appropriate section or note number.</p>
<h2 data-number="7.1" id="ft-macro"><span class="header-section-number">7.1</span> Feature test macro<a href="#ft-macro" class="self-link"></a></h2>
<p><em>Note to editor:</em> Add the macro below to the appropriate place
in <span>17.3.2
<a href="https://wg21.link/version.syn">[version.syn]</a></span>,
respecting alphabetical order.<br />
Also, set the value of the macro to the date of adoption.</p>
<div class="add" style="color: #006e28">

<div class="sourceCode" id="cb8"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a>#define __cpp_lib_fstream_native_handle 202XXXL  // also in &lt;fstream&gt;</span></code></pre></div>

</div>
<h2 data-number="7.2" id="add-the-following-section-into-file-based-streams-file.streams"><span class="header-section-number">7.2</span> Add the following section into
<em>File-based streams</em> <span>31.10
<a href="https://wg21.link/file.streams">[file.streams]</a></span><a href="#add-the-following-section-into-file-based-streams-file.streams" class="self-link"></a></h2>
<p>This section is to come between <span>31.10.1
<a href="https://wg21.link/fstream.syn">[fstream.syn]</a></span> and
<span>31.10.2
<a href="https://wg21.link/filebuf">[filebuf]</a></span>.</p>
<div class="add" style="color: #006e28">

<blockquote>
<p><strong>�.�.� Native handles [file.native]</strong></p>
<p> Several classes described in [file.streams] have a member
<code class="sourceCode default">native_handle_type</code>.</p>
<p> The type <code class="sourceCode default">native_handle_type</code>
represents a platform-specific <em>native handle</em> to a file. It is
trivially copyable and models
<code class="sourceCode default">semiregular</code>.</p>
<p> [ <em>Note �:</em> For operating systems based on POSIX,
<code class="sourceCode default">native_handle_type</code> is
<code class="sourceCode default">int</code>. For Windows-based operating
systems, <code class="sourceCode default">native_handle_type</code> is
<code class="sourceCode default">HANDLE</code>. — <em>end note</em>
]</p>
</blockquote>

</div>
<h2 data-number="7.3" id="modify-class-template-basic_filebuf-filebuf"><span class="header-section-number">7.3</span> Modify <em>Class template
<code class="sourceCode default">basic_filebuf</code></em> <span>31.10.2
<a href="https://wg21.link/filebuf">[filebuf]</a></span><a href="#modify-class-template-basic_filebuf-filebuf" class="self-link"></a></h2>
<div>
<div class="sourceCode" id="cb9"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>namespace std {</span>
<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a>  template&lt;class charT, class traits = char_traits&lt;charT&gt;&gt;</span>
<span id="cb9-3"><a href="#cb9-3" aria-hidden="true" tabindex="-1"></a>  class basic_filebuf : public basic_streambuf&lt;charT, traits&gt; {</span>
<span id="cb9-4"><a href="#cb9-4" aria-hidden="true" tabindex="-1"></a>  public:</span>
<span id="cb9-5"><a href="#cb9-5" aria-hidden="true" tabindex="-1"></a>    using char_type   = charT;</span>
<span id="cb9-6"><a href="#cb9-6" aria-hidden="true" tabindex="-1"></a>    using int_type    = typename traits::int_type;</span>
<span id="cb9-7"><a href="#cb9-7" aria-hidden="true" tabindex="-1"></a>    using pos_type    = typename traits::pos_type;</span>
<span id="cb9-8"><a href="#cb9-8" aria-hidden="true" tabindex="-1"></a>    using off_type    = typename traits::off_type;</span>
<span id="cb9-9"><a href="#cb9-9" aria-hidden="true" tabindex="-1"></a>    using traits_type = traits;</span>
<span id="cb9-10"><a href="#cb9-10" aria-hidden="true" tabindex="-1"></a><span class="va">+   using native_handle_type = <em>implementation-defined</em>; // see [file.native]</span></span>
<span id="cb9-11"><a href="#cb9-11" aria-hidden="true" tabindex="-1"></a>    </span>
<span id="cb9-12"><a href="#cb9-12" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb9-13"><a href="#cb9-13" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb9-14"><a href="#cb9-14" aria-hidden="true" tabindex="-1"></a>    // [filebuf.members], members</span>
<span id="cb9-15"><a href="#cb9-15" aria-hidden="true" tabindex="-1"></a>    bool is_open() const;</span>
<span id="cb9-16"><a href="#cb9-16" aria-hidden="true" tabindex="-1"></a>    basic_filebuf* open(const char* s, ios_base::openmode mode);</span>
<span id="cb9-17"><a href="#cb9-17" aria-hidden="true" tabindex="-1"></a>    basic_filebuf* open(const filesystem::path::value_type* s,</span>
<span id="cb9-18"><a href="#cb9-18" aria-hidden="true" tabindex="-1"></a>                        ios_base::openmode mode);  // wide systems only; see 31.10.1</span>
<span id="cb9-19"><a href="#cb9-19" aria-hidden="true" tabindex="-1"></a>    basic_filebuf* open(const string&amp; s,</span>
<span id="cb9-20"><a href="#cb9-20" aria-hidden="true" tabindex="-1"></a>                        ios_base::openmode mode);</span>
<span id="cb9-21"><a href="#cb9-21" aria-hidden="true" tabindex="-1"></a>    basic_filebuf* open(const filesystem::path&amp; s,</span>
<span id="cb9-22"><a href="#cb9-22" aria-hidden="true" tabindex="-1"></a>                        ios_base::openmode mode);</span>
<span id="cb9-23"><a href="#cb9-23" aria-hidden="true" tabindex="-1"></a>    basic_filebuf* close();</span>
<span id="cb9-24"><a href="#cb9-24" aria-hidden="true" tabindex="-1"></a><span class="va">+   native_handle_type native_handle() const noexcept;</span></span>
<span id="cb9-25"><a href="#cb9-25" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb9-26"><a href="#cb9-26" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb9-27"><a href="#cb9-27" aria-hidden="true" tabindex="-1"></a>  }</span>
<span id="cb9-28"><a href="#cb9-28" aria-hidden="true" tabindex="-1"></a>}</span></code></pre></div>
</div>
<h2 data-number="7.4" id="modify-class-template-basic_filebuf-filebuf-1"><span class="header-section-number">7.4</span> Modify <em>Class template
<code class="sourceCode default">basic_filebuf</code></em> <span>31.10.2
<a href="https://wg21.link/filebuf">[filebuf]</a></span><a href="#modify-class-template-basic_filebuf-filebuf-1" class="self-link"></a></h2>
<blockquote>
<p> An instance of <code class="sourceCode default">basic_filebuf</code>
behaves as described in [filebuf] provided
<code class="sourceCode default">traits::pos_type</code> is
<code class="sourceCode default">fpos&lt;traits::state_type&gt;</code>.
Otherwise the behavior is undefined.</p>
<div class="add" style="color: #006e28">
<p> The file associated with a
<code class="sourceCode default">basic_filebuf</code> has an associated
value of type
<code class="sourceCode default">native_handle_type</code>, called the
native handle of that file. This native handle can be obtained by
calling the member function
<code class="sourceCode default">native_handle</code>.</p>
<p> For any opened <code class="sourceCode default">basic_filebuf</code>
<code class="sourceCode default">f</code>, the native handle returned by
<code class="sourceCode default">f.native_handle()</code> is invalidated
when <code class="sourceCode default">f.close()</code> is called, or
<code class="sourceCode default">f</code> is destroyed.</p>
</div>
<p> In order to support file I/O and multibyte/wide character
conversion, conversions are performed using members of a facet, referred
to as <code class="sourceCode default">a_codecvt</code> in the following
subclauses, obtained as if by…</p>
</blockquote>
<h2 data-number="7.5" id="add-to-the-end-of-member-functions-filebuf.members"><span class="header-section-number">7.5</span> Add to the end of <em>Member
functions</em> <span>31.10.2.4
<a href="https://wg21.link/filebuf.members">[filebuf.members]</a></span><a href="#add-to-the-end-of-member-functions-filebuf.members" class="self-link"></a></h2>
<p><em>Note:</em> This would come after the defintion of
<code class="sourceCode default">basic_filebuf::close()</code>.</p>
<div class="add" style="color: #006e28">

<blockquote>
<div class="sourceCode" id="cb10"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb10-1"><a href="#cb10-1" aria-hidden="true" tabindex="-1"></a>native_handle_type native_handle() const noexcept;</span></code></pre></div>
<p> <em>Preconditions:</em>
<code class="sourceCode default">is_open()</code> is
<code class="sourceCode default">true</code>.</p>
<p> <em>Returns:</em> The native handle associated with
<code class="sourceCode default">*this</code>.</p>
</blockquote>

</div>
<h2 data-number="7.6" id="modify-class-template-basic_ifstream-ifstream"><span class="header-section-number">7.6</span> Modify <em>Class template
<code class="sourceCode default">basic_ifstream</code></em>
<span>31.10.3
<a href="https://wg21.link/ifstream">[ifstream]</a></span><a href="#modify-class-template-basic_ifstream-ifstream" class="self-link"></a></h2>
<div>
<div class="sourceCode" id="cb11"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb11-1"><a href="#cb11-1" aria-hidden="true" tabindex="-1"></a>namespace std {</span>
<span id="cb11-2"><a href="#cb11-2" aria-hidden="true" tabindex="-1"></a>  template&lt;class charT, class traits = char_traits&lt;charT&gt;&gt;</span>
<span id="cb11-3"><a href="#cb11-3" aria-hidden="true" tabindex="-1"></a>  class basic_ifstream : public basic_istream&lt;charT, traits&gt; {</span>
<span id="cb11-4"><a href="#cb11-4" aria-hidden="true" tabindex="-1"></a>  public:</span>
<span id="cb11-5"><a href="#cb11-5" aria-hidden="true" tabindex="-1"></a>    using char_type   = charT;</span>
<span id="cb11-6"><a href="#cb11-6" aria-hidden="true" tabindex="-1"></a>    using int_type    = typename traits::int_type;</span>
<span id="cb11-7"><a href="#cb11-7" aria-hidden="true" tabindex="-1"></a>    using pos_type    = typename traits::pos_type;</span>
<span id="cb11-8"><a href="#cb11-8" aria-hidden="true" tabindex="-1"></a>    using off_type    = typename traits::off_type;</span>
<span id="cb11-9"><a href="#cb11-9" aria-hidden="true" tabindex="-1"></a>    using traits_type = traits;</span>
<span id="cb11-10"><a href="#cb11-10" aria-hidden="true" tabindex="-1"></a><span class="va">+   using native_handle_type =</span></span>
<span id="cb11-11"><a href="#cb11-11" aria-hidden="true" tabindex="-1"></a><span class="va">+     typename basic_filebuf&lt;charT, traits&gt;::native_handle_type;</span></span>
<span id="cb11-12"><a href="#cb11-12" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-13"><a href="#cb11-13" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb11-14"><a href="#cb11-14" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-15"><a href="#cb11-15" aria-hidden="true" tabindex="-1"></a>    // [ifstream.members], members</span>
<span id="cb11-16"><a href="#cb11-16" aria-hidden="true" tabindex="-1"></a>    basic_filebuf&lt;charT, traits&gt;* rdbuf() const;</span>
<span id="cb11-17"><a href="#cb11-17" aria-hidden="true" tabindex="-1"></a><span class="va">+   native_handle_type native_handle() const noexcept;</span></span>
<span id="cb11-18"><a href="#cb11-18" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb11-19"><a href="#cb11-19" aria-hidden="true" tabindex="-1"></a>    bool is_open() const;</span>
<span id="cb11-20"><a href="#cb11-20" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb11-21"><a href="#cb11-21" aria-hidden="true" tabindex="-1"></a>  }</span>
<span id="cb11-22"><a href="#cb11-22" aria-hidden="true" tabindex="-1"></a>}</span></code></pre></div>
</div>
<h2 data-number="7.7" id="add-to-member-functions-ifstream.members"><span class="header-section-number">7.7</span> Add to <em>Member
functions</em> <span>31.10.3.4
<a href="https://wg21.link/ifstream.members">[ifstream.members]</a></span><a href="#add-to-member-functions-ifstream.members" class="self-link"></a></h2>
<blockquote>
<div class="sourceCode" id="cb12"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb12-1"><a href="#cb12-1" aria-hidden="true" tabindex="-1"></a>basic_filebuf&lt;charT, traits&gt;* rdbuf() const;</span></code></pre></div>
<p> <em>Returns:</em> <code class="sourceCode default">const_cast&lt;basic_filebuf&lt;charT, traits&gt;*&gt;(addressof(sb))</code>.</p>
</blockquote>
<div class="add" style="color: #006e28">

<blockquote>
<div class="sourceCode" id="cb13"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a>native_handle_type native_handle() const noexcept;</span></code></pre></div>
<p> <em>Effects:</em> Equivalent to: <code class="sourceCode default">return rdbuf()-&gt;native_handle();</code></p>
</blockquote>

</div>
<blockquote>
<div class="sourceCode" id="cb14"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a>bool is_open() const;</span></code></pre></div>
<p> <em>Returns:</em>
<code class="sourceCode default">rdbuf()-&gt;is_open()</code>.</p>
</blockquote>
<h2 data-number="7.8" id="modify-class-template-basic_ofstream-ofstream"><span class="header-section-number">7.8</span> Modify <em>Class template
<code class="sourceCode default">basic_ofstream</code></em>
<span>31.10.4
<a href="https://wg21.link/ofstream">[ofstream]</a></span><a href="#modify-class-template-basic_ofstream-ofstream" class="self-link"></a></h2>
<div>
<div class="sourceCode" id="cb15"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb15-1"><a href="#cb15-1" aria-hidden="true" tabindex="-1"></a>namespace std {</span>
<span id="cb15-2"><a href="#cb15-2" aria-hidden="true" tabindex="-1"></a>  template&lt;class charT, class traits = char_traits&lt;charT&gt;&gt;</span>
<span id="cb15-3"><a href="#cb15-3" aria-hidden="true" tabindex="-1"></a>  class basic_ofstream : public basic_ostream&lt;charT, traits&gt; {</span>
<span id="cb15-4"><a href="#cb15-4" aria-hidden="true" tabindex="-1"></a>  public:</span>
<span id="cb15-5"><a href="#cb15-5" aria-hidden="true" tabindex="-1"></a>    using char_type   = charT;</span>
<span id="cb15-6"><a href="#cb15-6" aria-hidden="true" tabindex="-1"></a>    using int_type    = typename traits::int_type;</span>
<span id="cb15-7"><a href="#cb15-7" aria-hidden="true" tabindex="-1"></a>    using pos_type    = typename traits::pos_type;</span>
<span id="cb15-8"><a href="#cb15-8" aria-hidden="true" tabindex="-1"></a>    using off_type    = typename traits::off_type;</span>
<span id="cb15-9"><a href="#cb15-9" aria-hidden="true" tabindex="-1"></a>    using traits_type = traits;</span>
<span id="cb15-10"><a href="#cb15-10" aria-hidden="true" tabindex="-1"></a><span class="va">+   using native_handle_type =</span></span>
<span id="cb15-11"><a href="#cb15-11" aria-hidden="true" tabindex="-1"></a><span class="va">+     typename basic_filebuf&lt;charT, traits&gt;::native_handle_type;</span></span>
<span id="cb15-12"><a href="#cb15-12" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb15-13"><a href="#cb15-13" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb15-14"><a href="#cb15-14" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb15-15"><a href="#cb15-15" aria-hidden="true" tabindex="-1"></a>    // [ofstream.members], members</span>
<span id="cb15-16"><a href="#cb15-16" aria-hidden="true" tabindex="-1"></a>    basic_filebuf&lt;charT, traits&gt;* rdbuf() const;</span>
<span id="cb15-17"><a href="#cb15-17" aria-hidden="true" tabindex="-1"></a><span class="va">+   native_handle_type native_handle() const noexcept;</span></span>
<span id="cb15-18"><a href="#cb15-18" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb15-19"><a href="#cb15-19" aria-hidden="true" tabindex="-1"></a>    bool is_open() const;</span>
<span id="cb15-20"><a href="#cb15-20" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb15-21"><a href="#cb15-21" aria-hidden="true" tabindex="-1"></a>  }</span>
<span id="cb15-22"><a href="#cb15-22" aria-hidden="true" tabindex="-1"></a>}</span></code></pre></div>
</div>
<h2 data-number="7.9" id="add-to-member-functions-ofstream.members"><span class="header-section-number">7.9</span> Add to <em>Member
functions</em> <span>31.10.4.4
<a href="https://wg21.link/ofstream.members">[ofstream.members]</a></span><a href="#add-to-member-functions-ofstream.members" class="self-link"></a></h2>
<p><em>Note:</em> These modifications are identical to those done to
<span>31.10.3.4
<a href="https://wg21.link/ifstream.members">[ifstream.members]</a></span>
above</p>
<blockquote>
<div class="sourceCode" id="cb16"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a>basic_filebuf&lt;charT, traits&gt;* rdbuf() const;</span></code></pre></div>
<p> <em>Returns:</em> <code class="sourceCode default">const_cast&lt;basic_filebuf&lt;charT, traits&gt;*&gt;(addressof(sb))</code>.</p>
</blockquote>
<div class="add" style="color: #006e28">

<blockquote>
<div class="sourceCode" id="cb17"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a>native_handle_type native_handle() const noexcept;</span></code></pre></div>
<p> <em>Effects:</em> Equivalent to: <code class="sourceCode default">return rdbuf()-&gt;native_handle();</code></p>
</blockquote>

</div>
<blockquote>
<div class="sourceCode" id="cb18"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb18-1"><a href="#cb18-1" aria-hidden="true" tabindex="-1"></a>bool is_open() const;</span></code></pre></div>
<p> <em>Returns:</em>
<code class="sourceCode default">rdbuf()-&gt;is_open()</code>.</p>
</blockquote>
<h2 data-number="7.10" id="modify-class-template-basic_fstream-fstream"><span class="header-section-number">7.10</span> Modify <em>Class template
<code class="sourceCode default">basic_fstream</code></em> <span>31.10.5
<a href="https://wg21.link/fstream">[fstream]</a></span><a href="#modify-class-template-basic_fstream-fstream" class="self-link"></a></h2>
<div>
<div class="sourceCode" id="cb19"><pre class="sourceCode diff"><code class="sourceCode diff"><span id="cb19-1"><a href="#cb19-1" aria-hidden="true" tabindex="-1"></a>namespace std {</span>
<span id="cb19-2"><a href="#cb19-2" aria-hidden="true" tabindex="-1"></a>  template&lt;class charT, class traits = char_traits&lt;charT&gt;&gt;</span>
<span id="cb19-3"><a href="#cb19-3" aria-hidden="true" tabindex="-1"></a>  class basic_fstream : public basic_iostream&lt;charT, traits&gt; {</span>
<span id="cb19-4"><a href="#cb19-4" aria-hidden="true" tabindex="-1"></a>  public:</span>
<span id="cb19-5"><a href="#cb19-5" aria-hidden="true" tabindex="-1"></a>    using char_type   = charT;</span>
<span id="cb19-6"><a href="#cb19-6" aria-hidden="true" tabindex="-1"></a>    using int_type    = typename traits::int_type;</span>
<span id="cb19-7"><a href="#cb19-7" aria-hidden="true" tabindex="-1"></a>    using pos_type    = typename traits::pos_type;</span>
<span id="cb19-8"><a href="#cb19-8" aria-hidden="true" tabindex="-1"></a>    using off_type    = typename traits::off_type;</span>
<span id="cb19-9"><a href="#cb19-9" aria-hidden="true" tabindex="-1"></a>    using traits_type = traits;</span>
<span id="cb19-10"><a href="#cb19-10" aria-hidden="true" tabindex="-1"></a><span class="va">+   using native_handle_type =</span></span>
<span id="cb19-11"><a href="#cb19-11" aria-hidden="true" tabindex="-1"></a><span class="va">+     typename basic_filebuf&lt;charT, traits&gt;::native_handle_type;</span></span>
<span id="cb19-12"><a href="#cb19-12" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb19-13"><a href="#cb19-13" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb19-14"><a href="#cb19-14" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb19-15"><a href="#cb19-15" aria-hidden="true" tabindex="-1"></a>    // [fstream.members], members</span>
<span id="cb19-16"><a href="#cb19-16" aria-hidden="true" tabindex="-1"></a>    basic_filebuf&lt;charT, traits&gt;* rdbuf() const;</span>
<span id="cb19-17"><a href="#cb19-17" aria-hidden="true" tabindex="-1"></a><span class="va">+   native_handle_type native_handle() const noexcept;</span></span>
<span id="cb19-18"><a href="#cb19-18" aria-hidden="true" tabindex="-1"></a><span class="va">+</span></span>
<span id="cb19-19"><a href="#cb19-19" aria-hidden="true" tabindex="-1"></a>    bool is_open() const;</span>
<span id="cb19-20"><a href="#cb19-20" aria-hidden="true" tabindex="-1"></a>    // ...</span>
<span id="cb19-21"><a href="#cb19-21" aria-hidden="true" tabindex="-1"></a>  }</span>
<span id="cb19-22"><a href="#cb19-22" aria-hidden="true" tabindex="-1"></a>}</span></code></pre></div>
</div>
<h2 data-number="7.11" id="add-to-member-functions-fstream.members"><span class="header-section-number">7.11</span> Add to <em>Member
functions</em> <span>31.10.5.4
<a href="https://wg21.link/fstream.members">[fstream.members]</a></span><a href="#add-to-member-functions-fstream.members" class="self-link"></a></h2>
<p><em>Note:</em> These modifications are identical to those done to
<span>31.10.3.4
<a href="https://wg21.link/ifstream.members">[ifstream.members]</a></span>
and <span>31.10.4.4
<a href="https://wg21.link/ofstream.members">[ofstream.members]</a></span>
above</p>
<blockquote>
<div class="sourceCode" id="cb20"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a>basic_filebuf&lt;charT, traits&gt;* rdbuf() const;</span></code></pre></div>
<p> <em>Returns:</em> <code class="sourceCode default">const_cast&lt;basic_filebuf&lt;charT, traits&gt;*&gt;(addressof(sb))</code>.</p>
</blockquote>
<div class="add" style="color: #006e28">

<blockquote>
<div class="sourceCode" id="cb21"><pre class="sourceCode default default"><code class="sourceCode default"><span id="cb21-1"><a href="#cb21-1" aria-hidden="true" tabindex="-1"></a>native_handle_type native_handle() const noexcept;</span></code></pre></div>
<p> <em>Effects:</em> Equivalent to: <code class="sourceCode default">return rdbuf()-&gt;native_handle();</code></p>
</blockquote>

</div>
<blockquote>
<div class="sourceCode" id="cb22"><pre class="sourceCode default"><code class="sourceCode default"><span id="cb22-1"><a href="#cb22-1" aria-hidden="true" tabindex="-1"></a>bool is_open() const;</span></code></pre></div>
<p> <em>Returns:</em>
<code class="sourceCode default">rdbuf()-&gt;is_open()</code>.</p>
</blockquote>
<h1 data-number="8" id="acknowledgements"><span class="header-section-number">8</span> Acknowledgements<a href="#acknowledgements" class="self-link"></a></h1>
<p>Thanks to Jonathan Wakely for reviewing the wording for R3 of this
paper.</p>
<p>Thanks to Niall Douglas for feedback, encouragement and ambitious
suggestions for this paper.</p>
<p>Thanks to the rest of the co-authors of <span class="citation" data-cites="P1750">[<a href="#ref-P1750" role="doc-biblioref">P1750R1</a>]</span> for the idea after cutting this
functionality out, especially to Jeff Garland for providing a heads-up
about a possible ABI-break that I totally would’ve missed, even though
it ended up being a non-issue.</p>
<p>Thanks to Michael Park for his paper markup framework <span class="citation" data-cites="mpark-wg21">[<a href="#ref-mpark-wg21" role="doc-biblioref">mpark/wg21</a>]</span>.</p>
<h1 data-number="9" id="bibliography"><span class="header-section-number">9</span> References<a href="#bibliography" class="self-link"></a></h1>
<div id="refs" class="references csl-bib-body hanging-indent" role="doc-bibliography">
<div id="ref-mpark-wg21" class="csl-entry" role="doc-biblioentry">
[mpark/wg21] mpark/wg21 on GitHub. <a href="https://github.com/mpark/wg21"><div class="csl-block">https://github.com/mpark/wg21</div></a>
</div>
<div id="ref-N4849" class="csl-entry" role="doc-biblioentry">
[N4849] Richard Smith. 2020-01-14. Working Draft, Standard for
Programming Language C++. <a href="https://wg21.link/n4849"><div class="csl-block">https://wg21.link/n4849</div></a>
</div>
<div id="ref-N4892" class="csl-entry" role="doc-biblioentry">
[N4892] Richard Smith. 2022. Working Draft, Standard for Programming
Language C++. <a href="https://wg21.link/N4892"><div class="csl-block">https://wg21.link/N4892</div></a>
</div>
<div id="ref-N4928" class="csl-entry" role="doc-biblioentry">
[N4928] Thomas Köppe. 2022. Working Draft, Standard for Programming
Language C++. <a href="https://wg21.link/N4928"><div class="csl-block">https://wg21.link/N4928</div></a>
</div>
<div id="ref-P1031" class="csl-entry" role="doc-biblioentry">
[P1031R2] Niall Douglas. 2019. Low level file i/o library. <a href="https://wg21.link/p1031r2"><div class="csl-block">https://wg21.link/p1031r2</div></a>
</div>
<div id="ref-P1750" class="csl-entry" role="doc-biblioentry">
[P1750R1] Klemens Morgernstern, Jeff Garland, Elias Kosunen, and Fatih
Bakir. 2019. A Proposal to Add Process Management to the C++ Standard
Library. <a href="https://wg21.link/p1750r1"><div class="csl-block">https://wg21.link/p1750r1</div></a>
</div>
<div id="ref-P2146" class="csl-entry" role="doc-biblioentry">
[P2146R2] Amanda Kornoushenko. 2020. Modern std::byte stream IO for C++.
<a href="https://wg21.link/p2146r2"><div class="csl-block">https://wg21.link/p2146r2</div></a>
</div>
</div>
</div>
</div>
</body>
</html>
