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<title>Issue 3878: import std; should guarantee initialization of standard iostreams objects</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#C++23">C++23</a> status.</em></p>
<h3 id="3878"><a href="lwg-defects.html#3878">3878</a>. <code>import std;</code> should guarantee initialization of standard iostreams objects</h3>
<p><b>Section:</b> 31.4.2 <a href="https://wg21.link/iostream.objects.overview">[iostream.objects.overview]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2023-02-09 <b>Last modified:</b> 2024-01-29</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#iostream.objects.overview">issues</a> in [iostream.objects.overview].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In the old world, <code>#include &lt;iostream></code>
behaves as if it defined a static-storage-duration <code>ios_base::Init</code> object, 
which causes the standard iostreams objects to be initialized (if necessary)
on startup and flushed on shutdown.
<p/>
But we don't include headers with <code>import std;</code>, so we need separate wording to
provide this guarantee. The proposed resolution below was adapted from a suggestion by 
Mathias Stearn on the reflector.
</p>
<p><i>[2023-02-09 Tim updates wording following LWG discussion]</i></p>


<p><i>[Issaquah 2023-02-09; LWG]</i></p>

<p>Move to Immediate for C++23</p>

<p><i>[2023-02-13 Approved at February 2023 meeting in Issaquah. Status changed: Immediate &rarr; WP.]</i></p>



<p id="res-3878"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4928" title=" Working Draft, Standard for Programming Language C++">N4928</a>.
</p>
<ol>
<li><p>Modify 31.4.2 <a href="https://wg21.link/iostream.objects.overview">[iostream.objects.overview]</a>p5  as indicated:</p>
<p>
-5- The results of including <code>&lt;iostream></code> in a translation unit shall be 
as if <code>&lt;iostream></code> defined an instance of <code>ios_base::Init</code> with static
storage duration. <ins>Each C++ library module (16.4.2.4 <a href="https://wg21.link/std.modules">[std.modules]</a>)
in a hosted implementation shall behave as if it contains an interface unit that defines
an unexported <code>ios_base::Init</code> variable with ordered initialization 
(6.10.3.3 <a href="https://wg21.link/basic.start.dynamic">[basic.start.dynamic]</a>). </ins>
<p/>
<ins>[<i>Note ?:</i> As a result, the definition of that variable is appearance-ordered
before any declaration following the point of importation of a C++ library module. 
Whether such a definition exists is unobservable by a program that does not reference
any of the standard iostream objects. &mdash; <i>end note</i>]</ins>
</p>
</li>
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