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POoperator= become to copy construtor in c++11 test
 

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  1. POoperator= become to copy construtor in c++11 test
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    <p>I have the following test in g++ 4.8.1 :</p> <p>g++ -std=c++11 testclass.cpp -o testclass.exe</p> <pre><code>template&lt;typename T&gt; class XRef { private : int inum ; T * ptr ; bool owner ; public : XRef(int i,T *ptrx):inum{i},ptr{ptrx},owner{true} {cout &lt;&lt; "natural" &lt;&lt; endl ;} XRef(XRef&amp; x):inum{x.inum},ptr{x.ptr},owner{false} {cout &lt;&lt; "copy" &lt;&lt; endl ;} XRef&amp; operator=(XRef&amp; x) { inum = x.inum ; ptr = x.ptr ; owner = false ; cout &lt;&lt; "assign" &lt;&lt; endl ; return *this ; } XRef(XRef&amp;&amp; x):inum{x.inum},ptr{move(x.ptr)},owner{true} {cout &lt;&lt; "move" &lt;&lt; endl ;} ~XRef() { if(owner) delete ptr ; } } ; int main() { char *ptr1 ; char *ptr2 ; ptr1 = (char *) malloc(100) ; ptr2 = (char *) malloc(100) ; XRef&lt;char&gt; x1 = XRef&lt;char&gt;(1,ptr1) ; cout &lt;&lt;"==============" &lt;&lt; endl ; XRef&lt;char&gt; x2 = x1 ; cout &lt;&lt;"==============" &lt;&lt; endl ; XRef&lt;char&gt; x3(x2) ; cout &lt;&lt;"==============" &lt;&lt; endl ; XRef&lt;char&gt; x4(XRef&lt;char&gt;(123,ptr2)) ; cout &lt;&lt;"==============" &lt;&lt; endl ; XRef&lt;char&gt; x5(move(XRef&lt;char&gt;(123,ptr2))) ; cout &lt;&lt;"==============" &lt;&lt; endl ; XRef&lt;char&gt; x6{123,ptr2} ; } </code></pre> <p>Then , the output :</p> <pre><code>natural ============== copy ============== copy ============== natural ============== natural move ============== natural </code></pre> <p>What surprise me is that : XRef x2 = x1 ; , I think this should call XRef&amp; operator=(XRef&amp; x) , but this test showes it call XRef(XRef&amp; x) instead .... </p> <p>I like to know what i do is wrong , so that operator= is not called !!</p> <p>Edit :</p> <pre><code>XRef&lt;char&gt; x7{123,ptr2} ; cout &lt;&lt;"==============" &lt;&lt; endl ; x7 = x6 ; cout &lt;&lt;"==============" &lt;&lt; endl ; </code></pre> <p>Showes :</p> <pre><code>natural ============== assign ============== </code></pre> <p>So , </p> <pre><code>XRef&lt;char&gt; x2 = x1 ; </code></pre> <p>is different with</p> <pre><code>XRef&lt;char&gt; x7{123,ptr2} ; x7 = x6 ; </code></pre> <p>How come this happened ?</p> <p>PS. I refered to : <a href="https://stackoverflow.com/questions/16865239/copy-construtor-called-extra?rq=1">copy construtor called extra</a> for reference ...</p>
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    1. USCommunity
    1. USbarfatchen
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    1. COThe line `XRef<char> x2 = x1 ;` is __creating a new object__ so the copy constructor is called (even though it looks something like an assignment). [See this related answer.](http://stackoverflow.com/a/5368273/445976)
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      1. POoperator= become to copy construtor in c++11 test
      1. USBlastfurnace
    2. COThank you,Blastfurnace,that is a excellent information to me ~!!
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      1. USbarfatchen
    3. COYour code has Undefined Behavior since it invokes double freeing memory.
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      1. USsoon
 

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