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POCopying and destruction when returning a C++ object
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  1. POCopying and destruction when returning a C++ object
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    copied!<p>I have a fairly simple piece of test code:</p> <pre><code>#include &lt;stdio.h&gt; class PG { public: PG(){ m_ptr = new int; printf("Created PG %i\n", (int)m_ptr); } ~PG(){ printf("Deleted PG %i\n", (int)m_ptr); delete (m_ptr); } PG&amp; operator =(const PG&amp; src) { printf("Copied PG %i %i\n", (int)m_ptr, (int)src.m_ptr); return(*this); } private: int * m_ptr; }; PG CreatePG() { PG ret; return ret; } int main(int argc, char* argv[]) { PG test; test = CreatePG(); printf("Ending\n"); return 0; } </code></pre> <p>If I compile this with GCC, VS2008 or VS2012 with full optimization and run it I get exactly what I expect:<br> Created PG 7837600 <em>-created test</em><br> Created PG 7689464 <em>-created ret</em><br> Copied PG 7837600 768946 <em>-copied ret to test</em><br> Deleted PG 7689464 <em>-deleted ret</em><br> Ending<br> Deleted PG 7837600 <em>-deleted test</em><br></p> <p>However when I compile on VS2008 or VS2012 with no optimization I get this:<br> Created PG 3888456 <em>-created test</em><br> Created PG 4036144 <em>-created ret</em><br> Deleted PG 4036144 <em>-deleted ret. Hang on, we haven't copied it yet!</em><br> Copied PG 3888456 4036144 <em>-We are now trying to copy deleted data</em><br> Deleted PG 4036144 <em>-This has already been deleted. The application crashes</em><br></p> <p>I can't believe that it is a bug in VS that has never been fixed but I also can't see what I am doing wrong. In my application I have an instance where this behaviour also occurs when compiling a more complicated class optimized for speed. I know it would be more efficient to use:</p> <pre><code> PG test = CreatePG(); </code></pre> <p>but I still get a similar problem though it is obviously using copy elision in this case:<br> Created PG 11228488<br> Deleted PG 11228488<br> Ending<br> Deleted PG 11228488<br> I am still getting the double delete.</p> <p>If anyone can throw some light on this I would be very grateful.</p>
 

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