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POboost::shared_ptr and Inheritance
 

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    <p>I am facing a situation in which I have a <code>std::vector</code> of <code>boost::shared_ptr</code>s of a base class. During the course of my program I need to store shared pointers to derived class objects in that vector too and at some time later in the program, need to retrieve those shared pointers.</p> <p>Following code illustrates my problem:</p> <pre><code>#include &lt;iostream&gt; #include &lt;vector&gt; using namespace std; #include &lt;boost/make_shared.hpp&gt; #include &lt;boost/foreach.hpp&gt; class Base { public: virtual ~Base() { } }; /******************************************/ typedef boost::shared_ptr&lt; Base &gt; BasePtr; /******************************************/ class Derived1 : public Base { public: void derived1_test() { cout &lt;&lt; "derived1_test" &lt;&lt; endl; } /******************************************/ int i1; }; /******************************************/ typedef boost::shared_ptr&lt; Derived1 &gt; Derived1Ptr; /******************************************/ class Derived2 : public Base { public: void derived2_test() { cout &lt;&lt; "derived2_test" &lt;&lt; endl; } /******************************************/ int i2; }; /******************************************/ typedef boost::shared_ptr&lt; Derived2 &gt; Derived2Ptr; /******************************************/ int main() { Derived1Ptr d1 = boost::make_shared&lt; Derived1 &gt;(); Derived2Ptr d2 = boost::make_shared&lt; Derived2 &gt;(); vector&lt; BasePtr &gt; v; v.push_back( d1 ); v.push_back( d2 ); BOOST_FOREACH(BasePtr bPtr, v) { try { Derived1&amp; d11 = dynamic_cast&lt; Derived1&amp; &gt;( *bPtr ); d11.derived1_test(); } catch (const std::bad_cast&amp; e) { Derived2&amp; d22 = dynamic_cast&lt; Derived2&amp; &gt;( *bPtr ); d22.derived2_test(); } } return 0; } </code></pre> <p>In the above code, if I change the code in <code>BOOST_FOREACH</code> from</p> <pre><code>Derived1&amp; d11 = dynamic_cast&lt; Derived1&amp; &gt;( *bPtr ); </code></pre> <p>to</p> <pre><code>Derived1Ptr d11 = dynamic_cast&lt; Derived1Ptr &gt;( bPtr ); </code></pre> <p>, I get following compile time error on VS2010</p> <pre><code>invalid target type for dynamic_cast target type must be a pointer or reference to a defined class </code></pre> <p>My problem is that I want to work with <code>boost::shared_ptr</code> not references. Secondly, I am using <code>dynamic_cast</code> which will throw a <code>std::bad_cast</code> exception when object reference is of a different type (tried using it with shared pointers but get the compiler error mentioned previously). That is clearly very slow. I want to be able to use a more performance oriented approach. What I am looking for here is any solution instead of using <code>dynamic_cast</code> and exception handling.</p> <p>Any suggestion with regards to code or change in design are welcome.</p>
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    1. COIf there is only one derived class or you are certain of it's type, you can just use `static_cast` to downcast.
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    2. COActually this is a much simpler version. In the actual code there are 3 different derived classes.
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    3. COAnd I realized that you are using `shared_ptr` not plain pointers, so disregard my advice.
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