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PONested templates gcc compiler 4.1.2 error
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  1. PONested templates gcc compiler 4.1.2 error
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    copied!<p>I'm trying to create a template class to insulate the users from a data type. I would have preferred to use an adapter class, but the function signatures needed to change requiring a template.</p> <p>In the code sample below(not the actual project just a simplified version to illustrate the problem), while in the main routine I'm able to use the ob_traits interface. But when I attempt to create the templated StructWrapper which uses the ob_traits as a base class, I get errors and gcc doesn't recognize the IntAdapter class created. This compiles on MSVC 8.0 but fails on gcc 4.1.2 20070626 ( Red hat 4.1.2-14)</p> <p>So two questions first, do you understand why the compile fails with the errors specified below?</p> <p>Second, any suggestions on how to implement this concept in a more simple manner?</p> <pre><code> #include &lt;iostream&gt; template &lt;typename T &gt; struct ob_traits { ob_traits( T&amp; param ) { value = param; }; T value; }; struct GeneralStructure { int a; GeneralStructure(int param):a(param){} }; struct DifferentStructure { GeneralStructure hidden; DifferentStructure( int param ):hidden(param){}; } ; /*template&lt; typename T &gt; struct ob_traits { }; */ template&lt;&gt; struct ob_traits&lt; GeneralStructure &gt; { struct IntAdapter { IntAdapter( GeneralStructure&amp; valueParam ):value(valueParam){} GeneralStructure value; int&amp; getValue() { return value.a; }; }; }; template&lt;&gt; struct ob_traits&lt; DifferentStructure &gt; { struct IntAdapter { IntAdapter( DifferentStructure&amp; valueParam):value( valueParam ){} DifferentStructure value; int&amp; getValue( ){ return value.hidden.a; }; }; void dump() { DifferentStructure testLocal(44); IntAdapter local( testLocal ); std::cout &lt;&lt; local.getValue()&lt;&lt;std::endl; } }; template &lt;typename T &gt; struct StructWrapper:public ob_traits&lt; T &gt; { StructWrapper(){}; /*main.cpp:60: error: 'IntAdapter' was not declared in this scope main.cpp:60: error: expected `;' before 'inner' main.cpp:60: error: 'inner' was not declared in this scope */ void dumpOuter(const T&amp; tempParam) { IntAdapter inner(tempParam); inner.dump(); }; /* main.cpp: In member function 'void StructWrapper&lt;T&gt;::dumpOuterFailsAsWell(const T&amp;)': main.cpp:66: error: expected `;' before 'inner' main.cpp:66: error: 'inner' was not declared in this scope */ void dumpOuterFailsAsWell(const T&amp; tempParam) { ob_traits&lt;T&gt;::IntAdapter inner(tempParam); inner.dump(); }; }; int main(int argc, char* argv[]) { GeneralStructure dummyGeneral(22); ob_traits&lt;struct GeneralStructure &gt;::IntAdapter test(dummyGeneral); DifferentStructure dummyDifferent(33); ob_traits&lt;struct DifferentStructure &gt;::IntAdapter test2(dummyDifferent); std::cout &lt;&lt; "GeneralStructure: "&lt;&lt;test.getValue()&lt;&lt;std::endl; std::cout &lt;&lt; "DifferentStructure: "&lt;&lt;test2.getValue()&lt;&lt;std::endl; ob_traits&lt;struct DifferentStructure &gt; test3; test3.dump(); std::cout &lt;&lt; "Test Templated\n"; return 0; } </code></pre>
 

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