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copied!<p>Check <a href="http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/" rel="noreferrer">this answer for C++11</a>. Basically, if you pass an lvalue the rvalue reference </p> <p>From <a href="http://blogs.msdn.com/b/xiangfan/archive/2012/02/03/c-98-gt-c-11-pass-by-value-or-pass-by-reference.aspx" rel="noreferrer">this article</a>:</p> <pre><code>void f1(String s) { vector<String> v; v.push_back(std::move(s)); } void f2(const String &s) { vector<String> v; v.push_back(s); } </code></pre> <p>"For lvalue argument, ‘f1’ has one extra copy to pass the argument because it is by-value, while ‘f2’ has one extra copy to call push_back. So no difference; for rvalue argument, the compiler has to create a temporary ‘String(L“”)’ and pass the temporary to ‘f1’ or ‘f2’ anyway. Because ‘f2’ can take advantage of move ctor when the argument is a temporary (which is an rvalue), the costs to pass the argument are the same now for ‘f1’ and ‘f2’."</p> <p>Continuing: " This means in C++11 we can get better performance by using pass-by-value approach when:</p> <ol> <li>The parameter type supports move semantics - All standard library components do in C++11</li> <li>The cost of move constructor is much cheaper than the copy constructor (both the time and stack usage).</li> <li>Inside the function, the parameter type will be passed to another function or operation which supports both copy and move.</li> <li>It is common to pass a temporary as the argument - You can organize you code to do this more.</li> </ol> <p>"</p> <p>OTOH, for C++98 it is best to pass by reference - less data gets copied around. Passing const or non const depend of whether you need to change the argument or not.</p>

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