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diff --git a/content/xdocs/BewareStdStringLiterals.html b/content/xdocs/BewareStdStringLiterals.html deleted file mode 100755 index b8388982c0..0000000000 --- a/content/xdocs/BewareStdStringLiterals.html +++ /dev/null @@ -1,69 +0,0 @@ -<html> - <head> - <title>Apache Qpid : BewareStdStringLiterals</title> - <link rel="stylesheet" href="styles/site.css" type="text/css" /> - <META http-equiv="Content-Type" content="text/html; charset=UTF-8"> - </head> - - <body> - <table class="pagecontent" border="0" cellpadding="0" cellspacing="0" width="100%" bgcolor="#ffffff"> - <tr> - <td valign="top" class="pagebody"> - <div class="pageheader"> - <span class="pagetitle"> - Apache Qpid : BewareStdStringLiterals - </span> - </div> - <div class="pagesubheading"> - This page last changed on Oct 19, 2006 by <font color="#0050B2">mmccorma</font>. - </div> - - <p>The short story: in C++ code using <tt>std::string</tt> never use string literals except to initialize static-scoped <tt>std::string</tt> constants.<br/> -(And by the way: <a href="http://cwiki.apache.org/confluence/display/qpid/NeverUseStaticLocalVariables" title="Visit page outside Confluence">NeverUseStaticLocalVariables</a></p> - -<p>The long story: <tt>std::string</tt> is all about avoiding copies. Reference counting and copy-on-write serve to maximise the sharing of a single heap-allocated char array while maintaining memory safety. When used consistently in a program it works rather nicely.</p> - -<p>However, when mixed with classic C-style string literals <tt>std::string</tt> can actually <em>cause</em> needless heap-allocated copies. Consider these innocent looking constructs:</p> - -<div class="code"><div class="codeContent"> -<pre class="code-java">void f(<span class="code-keyword">const</span> std::string& s);
-void g(<span class="code-keyword">const</span> std::string& s = <span class="code-quote">"hello"</span>);
-std::string h() { <span class="code-keyword">return</span> <span class="code-quote">"foo"</span>; }
-
-void copy_surprise {
- std::string x = <span class="code-quote">"x"</span>; <span class="code-comment">// 1
-</span> f(<span class="code-quote">"y"</span>); <span class="code-comment">// 2
-</span> g(); <span class="code-comment">// 3
-</span> x = h(); <span class="code-comment">//4
-</span> <span class="code-keyword">while</span> (x != <span class="code-quote">"end"</span>) { ... } <span class="code-comment">// 4
-</span>}</pre> -</div></div> - -<p>Lines 1-4 all cause creation and destruction of an implicit temporary <tt>std::string</tt> to hold the literal value. Line 5 does this for every execution of the while loop. That's a new/memcpy/delete each time. The heap is a heavily used resource, in tight inner loops in multi-threaded code this can be a <em>severe</em> contention bottleneck that cripples scalability.</p> - -<p>Use static class <tt>std::string</tt> constants or file-private constants instead. You can make global declarations file-private by using a nameless namespace (this is preferred over the use of the <tt>static</tt> keyword.)</p> - -<div class="code"><div class="codeContent"> -<pre class="code-java">namespace {
- <span class="code-keyword">const</span> std::string end(<span class="code-quote">"end"</span>);
-}
-void f() { std::string x; <span class="code-keyword">while</span> (x != end) {...} }</pre> -</div></div> - -<p>And once again <a href="http://cwiki.apache.org/confluence/display/qpid/NeverUseStaticLocalVariables" title="Visit page outside Confluence">NeverUseStaticLocalVariables</a></p> - - - - </td> - </tr> - </table> - <table border="0" cellpadding="0" cellspacing="0" width="100%"> - <tr> - <td height="12" background="border/border_bottom.gif"><img src="border/spacer.gif" width="1" height="1" border="0"/></td> - </tr> - <tr> - <td align="center"><font color="grey">Document generated by Confluence on Apr 22, 2008 02:47</font></td> - </tr> - </table> - </body> -</html>
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