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POAvoiding copying upon returning from a function - without relying on compiler optimizations
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  1. POAvoiding copying upon returning from a function - without relying on compiler optimizations
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    copied!<p>In this code, a huge vector <em>could be</em> (depending on compiler) copied upon return:</p> <pre><code>vector&lt;string&gt; foo() { vector&lt;string&gt; vec; //make vec huge return vec; } vector&lt;string&gt; bar = foo(); </code></pre> <p>How do I avoid copying the vector, <strong>without relying on compiler optimizations</strong>?</p> <p>Now, understand that this is just a simple example, with a single return statement. But for more complex cases, it is a possibility that even good compilers will not be able to do optimizations to avoid copying the vector. (<a href="https://stackoverflow.com/a/10479595/1859852">This answer</a> to another question mentions one such case.)</p> <p>(Relying on compiler optimizations always seemed rather strange to me in the first place, since I'm supposed to be writing <strong>good, portable, C++ code</strong>, as opposed to worrying about how this and that compiler does things under the hood. All those "compiler optimization" answers to the other questions therefore puzzle me.)</p> <p>One idea I came up with so far is to use C++11's smart pointers:</p> <pre><code>shared_ptr&lt;vector&lt;string&gt;&gt; foo() { shared_ptr&lt;vector&lt;string&gt;&gt; vec_ptr = make_shared&lt;vector&lt;string&gt;&gt;(); //make *vec_ptr (i.e. the actual vector) huge return vec_ptr; } shared_ptr&lt;vector&lt;string&gt;&gt; bar_ptr = foo(); //now, *bar_ptr is the underlying vector we can use </code></pre> <p>It looks like this will avoid the copy in all cases. The problem is that this code is getting to be quite cumbersome.</p> <p>Any good non-cumbersome alternatives? Supposedly, C++11 provides some new "move" functionality through rvalue references. Could those help?</p>
 

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