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POC++ copy constructor invocation
 

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    <p>As far as i know, a copy constructor is invoked in the following scenarios :</p> <pre><code>1) Pass by value 2) Return by value 3) When you create and initialize a new object with an existing object </code></pre> <p>Here's the program :</p> <pre><code>#include &lt;iostream&gt; using namespace std; class Example { public: Example() { cout &lt;&lt; "Default constructor called.\n"; } Example(const Example &amp;ob1) { cout &lt;&lt; "Copy constructor called.\n"; } Example&amp; operator=(const Example &amp;ob1) { cout &lt;&lt; "Assignment operator called.\n"; return *this; } ~Example() { cout&lt;&lt;"\nDtor invoked"&lt;&lt;endl; } int aa; }; Example funct() { Example ob2; ob2.aa=100; return ob2; } int main() { Example x; cout &lt;&lt; "Calling funct..\n"; x = funct(); return 0; } </code></pre> <p>The output is:</p> <blockquote> <p>Default constructor called.</p> <p>Calling funct..</p> <p>Default constructor called.</p> <p>Assignment operator called.</p> <p>Dtor invoked</p> <p>Dtor invoked</p> </blockquote> <p>Please correct me, IIRC the following sequence of calls should occur :</p> <p>1) Constructor of x is called</p> <p>2) Constructor of ob2 is called</p> <p>3) The function returns and so copy constructor is invoked (to copy ob2 to unnamed temporary variable i.e funct() )</p> <p>4) Destructor of ob2 called </p> <p>5) Assign the unnamed temporary variable to x</p> <p>6) Destroy temporary variable i.e invoke its destructor</p> <p>7) Destroy x i.e invoke x's destructor</p> <p>But then why copy constructor is not invoked and also only 2 calls to dtors are there whereas i expect 3.</p> <p>I know compiler can do optimizations, however, is my understanding correct ?</p> <p>Thanks a lot :)</p> <p>Regards</p> <p>lali</p>
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    1. COHere's an interesting article on this topic: http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/
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    2. COThere's no real question here... Check your compiler documentation, because Copy-const can be optimized (as you already told us)
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    3. COYup, the behaviour is due to return value optimization, thanks a lot for pointing it out. The program behaves as expected when compiled with -fno-elide-constructors on gcc. Thanks to UncleBens for that :)
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