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POProblems with shared_ptr<T[]> wrapping a dynamic array
 

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  1. POProblems with shared_ptr<T[]> wrapping a dynamic array
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    <p>I wanted to replace some raw pointers in my class with a <code>std::shared_ptr</code> so that I don't have to worry when I create copies of that class. But the raw pointers point to a dynamic array. Using a shared_ptr with dynamic arrays is possible when you give it a custom deleter, e.&thinsp;g. <code>default_delete&lt;T[]&gt;</code>.</p> <p>But I get a big error list as soon as I try to assign a new value to that field, even on construction.</p> <p>Here's a minimal code sample:</p> <pre><code>#include &lt;memory&gt; #include &lt;cstddef&gt; using namespace std; template&lt;typename T&gt; shared_ptr&lt;T[]&gt; make_shared_array(size_t size) { return shared_ptr&lt;T[]&gt;(new T[size], default_delete&lt;T[]&gt;()); } struct Foo { shared_ptr&lt;char[]&gt; field; }; int main() { Foo a; // This line produces the error. a.field = make_shared_array&lt;char&gt;(256); return 0; } </code></pre> <hr> <p><strong>NB:</strong> Yes, I know that I could/should <code>vector</code> instead of dynamic arrays. But their performance is not the same. I do some heavy image processing and the arrays hold the pixels. On less than VGA resolution the processing time increased from 8 to 11&thinsp;s. That's quite a lot.</p> <hr> <p><strong>Update:</strong> Of course I can provide the errors here. I just didn't know if I should clutter the problem description with it. But here it is:</p> <blockquote> <p>C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(754) : error C2664: 'std::_Ptr_base&lt;_Ty>::_Reset0' : cannot convert parameter 1 from 'char <em>' to 'char (</em>)[]'<br> with<br> [<br> _Ty=char []<br> ]<br> Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast<br> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(723) : see reference to function template instantiation 'void std::shared_ptr&lt;_Ty>::_Resetp0&lt;_Ux>(_Ux *,std::_Ref_count_base *)' being compiled<br> with<br> [<br> _Ty=char [],<br> _Ux=char<br> ]<br> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(723) : see reference to function template instantiation 'void std::shared_ptr&lt;_Ty>::_Resetp0&lt;_Ux>(_Ux *,std::_Ref_count_base *)' being compiled<br> with<br> [<br> _Ty=char [],<br> _Ux=char<br> ]<br> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(494) : see reference to function template instantiation 'void std::shared_ptr&lt;_Ty>::_Resetp&lt;_Ux,_Dx>(_Ux *,_Dx)' being compiled<br> with<br> [<br> _Ty=char [],<br> _Ux=char,<br> _Dx=std::default_delete<br> ]<br> C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\INCLUDE\memory(494) : see reference to function template instantiation 'void std::shared_ptr&lt;_Ty>::_Resetp&lt;_Ux,_Dx>(_Ux *,_Dx)' being compiled<br> with<br> [<br> _Ty=char [],<br> _Ux=char,<br> _Dx=std::default_delete<br> ]<br> problem.cpp(9) : see reference to function template instantiation 'std::shared_ptr&lt;_Ty>::shared_ptr>(_Ux *,_Dx)' being compiled<br> with<br> [<br> _Ty=char [],<br> T=char,<br> _Ux=char,<br> _Dx=std::default_delete<br> ]<br> problem.cpp(9) : see reference to function template instantiation 'std::shared_ptr&lt;_Ty>::shared_ptr>(_Ux *,_Dx)' being compiled<br> with<br> [<br> _Ty=char [],<br> T=char,<br> _Ux=char,<br> _Dx=std::default_delete<br> ]<br> problem.cpp(21) : see reference to function template instantiation 'std::shared_ptr&lt;_Ty> make_shared_array(size_t)' being compiled<br> with<br> [<br> _Ty=char []<br> ] </p> </blockquote>
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    1. COWould you, perchance, share this "big error list?"
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    2. COI hear this "their performance is not the same" quite often, can you show some evidence? I have tried quite hard, testing all kinds of operations, but all my results always result in both being of exactly the same speed...
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      1. POProblems with shared_ptr<T[]> wrapping a dynamic array
      1. USPlasmaHH
    3. COif using vector::reserve when initializing the vector (or simply initializing it to a fixed size) the performance should be "close enough to same"
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      1. POProblems with shared_ptr<T[]> wrapping a dynamic array
      1. USeladidan
 

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