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<title>Issue 1435: Unclear returns specifications for C99 complex number functions</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++11">C++11</a> status.</em></p>
<h3 id="1435"><a href="lwg-defects.html#1435">1435</a>. Unclear returns specifications for C99 complex number functions</h3>
<p><b>Section:</b> 29.4.7 <a href="https://wg21.link/complex.value.ops">[complex.value.ops]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <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#complex.value.ops">issues</a> in [complex.value.ops].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses GB-120</b></p>

<p>
The complex number functions added for compatibility
with the C99 standard library are defined purely as a
cross-reference, with no hint of what they should return.
This is distinct from the style of documentation for the
functions in the earlier standard. In the case of the
inverse-trigonometric and hyperbolic functions, a
reasonable guess of the functionality may be made from
the name, this is not true of the cproj function, which
apparently returns the projection on the Reimann Sphere.
A single line description of each function, associated with
the cross-reference, will greatly improve clarity.
</p>

<p><i>[2010-11-06 Beman provides proposed resolution wording.]</i></p>


<p><i>[
2010 Batavia: The working group concurred with the issue's Proposed Resolution
]</i></p>


<p><i>[
Adopted at 2010-11 Batavia
]</i></p>




<p id="res-1435"><b>Proposed resolution:</b></p>

<p><i>Change 26.4.7 complex value operations [complex.value.ops] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; proj(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i> the projection of <code>x</code> onto the Riemann 
    sphere.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>cproj</code>, 
    defined in 7.3.9.4.</p>
  </blockquote>
</blockquote>

<p><i>Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; acos(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i>&nbsp; the complex arc cosine  of <code>x</code>.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>cacos</code>, 
    defined in 7.3.5.1.</p>
  </blockquote>
</blockquote>

<p><i>Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; asin(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i>&nbsp; the complex arc sine  of <code>x</code>.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>casin</code>, 
    defined in 7.3.5.2.</p>
  </blockquote>
</blockquote>

<p><i>Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; atan(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i>&nbsp; the complex arc tangent  of <code>x</code>.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>catan</code>, 
    defined in 7.3.5.3.</p>
  </blockquote>
</blockquote>

<p><i>Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; acosh(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i>&nbsp; the complex arc hyperbolic cosine of
    <code>x</code>.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>cacosh</code>, 
    defined in 7.3.6.1.</p>
  </blockquote>
</blockquote>

<p><i>Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; asinh(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i>&nbsp; the complex arc hyperbolic sine  of <code>
    x</code>.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>casinh</code>, 
    defined in 7.3.6.2.</p>
  </blockquote>
</blockquote>

<p><i>Change 26.4.8 complex transcendentals [complex.transcendentals] as indicated:</i></p>
<blockquote>
  <p><code>template&lt;class T&gt; complex&lt;T&gt; atanh(const complex&lt;T&gt;&amp; x);</code></p>
  <blockquote>
    <p><ins><i>Returns:</i>&nbsp; the complex arc hyperbolic tangent  of
    <code>x</code>.</ins></p>
    <p><del><i>Effects:</i></del> <ins><i>Remarks:</i></ins> Behaves the same as the C function <code>catanh</code>, 
    defined in 7.3.6.2.</p>
  </blockquote>
</blockquote>







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