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POCopy constructor strange behavior when returning-by-value
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  1. POCopy constructor strange behavior when returning-by-value
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    copied!<p>I tested the behavior of copy constructor with functions that return an object by value, and I came across a case where copy constructor does get invoked and a case it doesn't.</p> <p>Please consider the following code:</p> <pre><code>class A { public: A() {} A(const A&amp; a) { cout &lt;&lt; "Copy CTOR: " &lt;&lt; "This address is " &lt;&lt; this &lt;&lt; " input address is "&lt;&lt; &amp;a &lt;&lt; "\n"; } }; A returnMyself(A&amp; a) { cout&lt;&lt;"Myself address is: "&lt;&lt; &amp;a &lt;&lt; "\n"; return a; } A returnLocal(A&amp; a) { A local; cout&lt;&lt;"local address in returnLocal is "&lt;&lt; &amp;local &lt;&lt; "\n"; return local; } int main () { A a; cout&lt;&lt;"Before returnMyself\n"; returnMyself(a); cout&lt;&lt;"After returnMyself\n\n"; cout&lt;&lt;"Before returnLocal\n"; returnLocal(a); cout&lt;&lt;"After returnLocal\n"; } </code></pre> <p>The output of <code>main</code> is:</p> <pre> Before returnMyself. Myself address is: 0x7fff6afd88f0. Copy CTOR Invoked: This address is 0x7fff6afd88d8. Input address is 0x7fff6afd88f0. After returnMyself. Before returnLocal. Local address in returnLocal is 0x7fff6afd88d0. After returnLocal. </pre> <p>As you can see, when I declare a local object and return it, copy constructor doesn't get invoked, as opposed to returning a given reference-object which does invoke copy constructor.</p> <p>Does anyone have an explanation for this? In general, what are the cases of invoking copy constructor from a function that returns-by-value?</p> <p>Thanks!</p>
 

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