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Add documentation for how to use the new LLVM streams.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@32390 91177308-0d34-0410-b5e6-96231b3b80d8
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Bill Wendling 2006-12-09 01:20:34 +00:00
parent 298feadd7a
commit 7f564c02cf
1 changed files with 74 additions and 2 deletions
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docs/CodingStandards.html
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@ -41,12 +41,15 @@
<li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
<li><a href="#hl_privateheaders">Keep "internal" Headers
Private</a></li>
<li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
<em>forbidden</em></a></li>
</ol></li>
<li><a href="#micro">The Low Level Issues</a>
<ol>
<li><a href="#ll_assert">Assert Liberally</a></li>
<li><a href="#ll_ns_std">Do not use 'using namespace std'</a></li>
<li><a href="#ll_virtual_anch">Provide a virtual method anchor for clases in headers</a></li>
<li><a href="#ll_virtual_anch">Provide a virtual method anchor for
clases in headers</a></li>
<li><a href="#ll_preincrement">Prefer Preincrement</a></li>
<li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
</ol></li>
@ -55,7 +58,8 @@
</ol>
<div class="doc_author">
<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
<a href="mailto:void@nondot.org">Bill Wendling</a></p>
</div>
@ -482,6 +486,73 @@ class itself... just make them private (or protected), and all is well.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is forbidden</a>
</div>
<div class="doc_text">
<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
support clients using LLVM libraries as part of larger systems. In particular,
we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
the static c'tors are run whenever an application start up that uses the dynamic
library. There are two problems with this:</p>
<ol>
<li>The time to run the static c'tors impacts startup time of
applications&mdash;a critical time for gui apps.</li>
<li>The static c'tors cause the app to pull many extra pages of memory off the
disk: both the code for the static c'tors in each .o file and the small
amount of data that gets touched. In addition, touched/dirty pages put
more pressure on the VM system on low-memory machines.</li>
</ol>
<table>
<tbody>
<tr>
<th>Old Way</th>
<th>New Way</th>
</tr>
<tr>
<td align="left"><pre>#include &lt;iostream&gt;</pre></td>
<td align="left"><pre>#include "llvm/Support/Streams.h"</pre></td>
</tr>
<tr>
<td align="left"><pre>DEBUG(std::cerr &lt;&lt; ...);</pre></td>
<td align="left"><pre>DOUT &lt;&lt; ...;</pre></td>
</tr>
<tr>
<td align="left"><pre>std::cerr &lt;&lt; "Hello world\n";</pre></td>
<td align="left"><pre>llvm::cerr &lt;&lt; "Hello world\n";</pre></td>
</tr>
<tr>
<td align="left"><pre>std::cout &lt;&lt; "Hello world\n";</pre></td>
<td align="left"><pre>llvm::cout &lt;&lt; "Hello world\n";</pre></td>
</tr>
<tr>
<td align="left"><pre>std::cin &gt;&gt; Var;</pre></td>
<td align="left"><pre>llvm::cin &gt;&gt; Var;</pre></td>
</tr>
<tr>
<td align="left"><pre>std::ostream</pre></td>
<td align="left"><pre>llvm::OStream</pre></td>
</tr>
<tr>
<td align="left"><pre>std::istream</pre></td>
<td align="left"><pre>llvm::IStream</pre></td>
</tr>
<tr>
<td align="left"><pre>std::stringstream</pre></td>
<td align="left"><pre>llvm::StringStream</pre></td>
</tr>
</tbody>
</table>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="micro">The Low Level Issues</a>
@ -631,6 +702,7 @@ it's better to use a literal <tt>'\n'</tt>.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="seealso">See Also</a>