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POstd::auto_ptr Compile Issue in Visual Studio 6.0
 

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  1. POstd::auto_ptr Compile Issue in Visual Studio 6.0
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    <p>Update: Edited code example to use AutoA for the workaround (which was the original intention). Realized this after seeing rlbond's answer.</p> <p>I am trying to incorporate the usage of <code>auto_ptr</code> in my code based on recommendations from this thread:</p> <p><a href="https://stackoverflow.com/questions/478482/express-the-usage-of-c-arguments-through-method-interfaces/478678">Express the usage of C++ arguments through method interfaces</a></p> <p>However, I am receiving some unexpected compile errors when compiling with Visual Studio 6.0. It has a problem when dealing with assignments/copies of a <code>std::auto_ptr</code> of a derived type to a <code>std::auto_ptr</code> of the base type. Is this an issue specific to my compiler?</p> <p>I know there's a strong recommendation to use Boost, but on my project it is not an option. If I still want to use <code>auto_ptr</code>, am I forced to use the workaround of calling <code>std::auto_ptr::release()</code>? From what I have encountered so far, this issue results in a compiler error, so it's easy enough to catch. However, could adopting the convention of calling release to assign to a 'auto_ptr' of base type throughout expose me to any maintenance issues? Especially if built with a different compiler (assuming other compilers don't have this issue).</p> <p>If the <code>release()</code> workaround is not good due to my circumstances, should I fall back on using a different convention for describing transfer of ownership?</p> <p>The following is an example illustrating the problem.</p> <pre><code>#include "stdafx.h" #include &lt;memory&gt; struct A { int x; }; struct B : public A { int y; }; typedef std::auto_ptr&lt;A&gt; AutoA; typedef std::auto_ptr&lt;B&gt; AutoB; void sink(AutoA a) { //Some Code.... } int main(int argc, char* argv[]) { //Raws to auto ptr AutoA a_raw_to_a_auto(new A()); AutoB b_raw_to_b_auto(new B()); AutoA b_raw_to_a_auto(new B()); //autos to same type autos AutoA a_auto_to_a_auto(a_raw_to_a_auto); AutoB b_auto_to_b_auto(b_raw_to_b_auto); //raw derive to auto base AutoB b_auto(new B()); //auto derive to auto base AutoA b_auto_to_a_auto(b_auto); //fails to compile //workaround to avoid compile error. AutoB b_workaround(new B()); AutoA b_auto_to_a_auto_workaround(b_workaround.release()); sink(a_raw_to_a_auto); sink(b_raw_to_b_auto); //fails to compile return 0; } </code></pre> <p>Compile Error:</p> <pre><code>Compiling... Sandbox.cpp C:\Program Files\Microsoft Visual Studio\MyProjects\Sandbox\Sandbox.cpp(40) : error C2664: '__thiscall std::auto_ptr&lt;struct A&gt;::std::auto_ptr&lt;struct A&gt;(struct A *)' : cannot convert parameter 1 from 'class std::auto_ptr&lt;struct B&gt;' to 'struct A *' No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called C:\Program Files\Microsoft Visual Studio\MyProjects\Sandbox\Sandbox.cpp(47) : error C2664: 'sink' : cannot convert parameter 1 from 'class std::auto_ptr&lt;struct B&gt;' to 'class std::auto_ptr&lt;struct A&gt;' No constructor could take the source type, or constructor overload resolution was ambiguous Error executing cl.exe. Sandbox.exe - 2 error(s), 0 warning(s) </code></pre>
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    1. COSeriously? an 11 years old compiler? You'd think people would move on.
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    2. COYou'd think there would be something to move to. 10 is the new 6, but 10 is still in beta.
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