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POC++ Tricky Inheritance Class Definition Problem
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  1. POC++ Tricky Inheritance Class Definition Problem
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    copied!<p>I'm getting this error when dealing with a number of classes including each other:</p> <pre><code>error: expected class-name before '{' token </code></pre> <p>I see what is going on, but I do not know how to properly correct it. Here is an abstracted version of the code:</p> <p><em>A.h</em></p> <pre><code>#ifndef A_H_ #define A_H_ #include "K.h" class A { public: A(); }; #endif /*A_H_*/ </code></pre> <p><em>A.cpp</em></p> <pre><code>#include "A.h" A::A() {} </code></pre> <p><em>B.h</em></p> <pre><code>#ifndef B_H_ #define B_H_ #include "A.h" class B : public A { // error: expected class-name before '{' token public: B(); }; #endif /*B_H_*/ </code></pre> <p><em>B.cpp</em></p> <pre><code>#include "B.h" B::B() : A() {} </code></pre> <p><em>J.h</em></p> <pre><code>#ifndef J_H_ #define J_H_ #include "B.h" class J { public: J(); }; #endif /*J_H_*/ </code></pre> <p><em>J.cpp</em></p> <pre><code>#include "J.h" J::J() {} </code></pre> <p><em>K.h</em></p> <pre><code>#ifndef K_H_ #define K_H_ #include "J.h" class K : public J { // error: expected class-name before '{' token public: K(); }; #endif /*K_H_*/ </code></pre> <p><em>K.cpp</em></p> <pre><code>#include "K.h" K::K() : J() {} </code></pre> <p><em>main.cpp</em></p> <pre><code>#include "A.h" int main() { return 0; } </code></pre> <hr> <p>Starting in <em>main.cpp</em>, I can determine that this is what the compiler sees:</p> <pre><code>#include "A.h" #ifndef A_H_ #define A_H_ #include "K.h" #ifndef K_H_ #define K_H_ #include "J.h" #ifndef J_H_ #define J_H_ #include "B.h" #ifndef B_H_ #define B_H_ #include "A.h" class B : public A { // error: expected class-name before '{' token </code></pre> <p>So, <em>A</em>'s definition is not complete when we get to <em>B</em>. I've been told that sometimes you need to use a forward declaration and then move the <em>#include</em> statement into the <em>.cpp</em> file, but I'm not having any luck with that. If I try anything like that, I simply get the additional error:</p> <pre><code>error: forward declaration of 'struct ClassName' </code></pre> <p>I think maybe I'm just not doing things in the right places. Can someone please show me how to get this code to compile? Thank you very much!</p> <hr> <p>Edit: I want to point out that this is just abstracted version of the real code. I realize that there are no references to <em>K</em> in <em>A</em> or <em>B</em> in <em>J</em>, but there are in the real code and I feel that they're completely necessary. Perhaps if I give a brief description of the real classes, someone can help me restructure or fix my code.</p> <p>Class <em>A</em> is an abstract node class that acts as an interface for nodes in a graph. Class <em>B</em> is one of what will be a number of different implementations of <em>A</em>. In the same manner, class <em>J</em> is an abstract Visitor class and <em>K</em> is the corresponding implementation. Here is the code with a little more context:</p> <p><em>A.h</em> (Abstract Node)</p> <pre><code>#ifndef A_H_ #define A_H_ #include "K.h" class K; class A { public: A(); virtual void accept(const K&amp;) const = 0; }; #endif /*A_H_*/ </code></pre> <p><em>A.cpp</em></p> <pre><code>#include "A.h" A::A() {} </code></pre> <p><em>B.h</em> (Concrete Node)</p> <pre><code>#ifndef B_H_ #define B_H_ #include "A.h" class K; class B : public A { // error: expected class-name before '{' token public: B(); virtual void accept(const K&amp;) const; }; #endif /*B_H_*/ </code></pre> <p><em>B.cpp</em></p> <pre><code>#include "B.h" B::B() : A() {} void B::accept(const K&amp; k) const { k.visit(this); } </code></pre> <p><em>J.h</em> (Abstract Visitor)</p> <pre><code>#ifndef J_H_ #define J_H_ #include "B.h" class B; class J { public: J(); virtual void visit(const B*) const = 0; }; #endif /*J_H_*/ </code></pre> <p><em>J.cpp</em></p> <pre><code>#include "J.h" J::J() {} </code></pre> <p><em>K.h</em> (Concrete Visitor)</p> <pre><code>#ifndef K_H_ #define K_H_ #include "J.h" class B; class K : public J { // error: expected class-name before '{' token public: K(); virtual void visit(const B*) const; }; #endif /*K_H_*/ </code></pre> <p><em>K.cpp</em></p> <pre><code>#include "K.h" K::K() : J() {} void K::visit(const B*) const {}; </code></pre> <p><em>main.cpp</em></p> <pre><code>#include "A.h" int main() { return 0; } </code></pre> <p>I had to add some forward declarations to make some additional errors that appeared (when I added detail) go away. Some of them may not be necessary or correct.</p>
 

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