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POFixing order of inclusion when there is circular dependency in C++ template classes
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  1. POFixing order of inclusion when there is circular dependency in C++ template classes
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    copied!<p>I came across a circular dependency issue, where the order of inclusion of headers matters. <a href="https://stackoverflow.com/questions/3353831/resolving-a-circular-dependency-between-template-classes">This</a> problem is similar, but it does not document the solution where one class instantiates an object of the other. </p> <p><strong>Problem:</strong> </p> <ul> <li>I have two classes: Foo and Bar. Bar is templatized. (Foo may or may not be templatized). </li> <li>Foo has an instance of Bar, and Bar has a pointer of type Foo, and the implementation of Bar needs to access members of Foo through this pointer. </li> <li>Foo and Bar have to be implemented <strong>within separate files</strong>. As Bar is templatized, its declaration and implementation have to be in the same file.</li> </ul> <p>In the following code, if main.cpp includes Bar.h before Foo.h the code compiles, and does not when Foo.h is included before Bar.h. <em>Is there a way to make the code compile, irrespective of the order in which headers are included in main.cpp?</em></p> <p><strong>Foo.h</strong></p> <pre><code>#ifndef FOO_H #define FOO_H #include"Bar.h" class Foo { public: Bar&lt;&gt; B; void fooStuff(){}; }; #endif </code></pre> <p><strong>Bar.h</strong></p> <pre><code>#ifndef BAR_H #define BAR_H class Foo; template&lt;int N=0&gt; class Bar { public: Foo * F; void barStuff(); }; #include"Foo.h" template&lt;int N&gt; void Bar&lt;N&gt;::barStuff() { F-&gt;fooStuff(); }; #endif </code></pre> <p><strong>main.cpp</strong></p> <pre><code>#include"Foo.h" #include"Bar.h" int main() { Foo F; F.B.barStuff(); }; </code></pre>
 

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