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POC++ operator overloading with inheritance
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  1. POC++ operator overloading with inheritance
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    copied!<p>Let's say I have a class called <code>Vehicle</code> and another called <code>Car</code> that extends <code>Vehicle</code> class. I want to implement <code>++</code> operators for both classes. </p> <pre><code>#include &lt;cstdio&gt; #include &lt;cmath&gt; #include &lt;cstring&gt; #include &lt;ctime&gt; #include &lt;iostream&gt; #include &lt;algorithm&gt; #include &lt;set&gt; #include &lt;map&gt; #include &lt;vector&gt; #include &lt;sstream&gt; #include &lt;typeinfo&gt; #define debug(args...) // Just strip off all debug tokens using namespace std; // CUT begin #define debug(args...) {dbg,args;cout&lt;&lt;endl;} struct debugger{template&lt;typename T&gt; debugger&amp; operator ,(const T&amp; v){cout&lt;&lt;v&lt;&lt;" ";return *this;}}dbg; template &lt;typename T1,typename T2&gt; inline ostream&amp; operator&lt;&lt;(ostream&amp; os,const pair&lt;T1,T2&gt;&amp; p){return os&lt;&lt;"("&lt;&lt;p.first&lt;&lt;", "&lt;&lt;p.second&lt;&lt;")";} template&lt;typename T&gt;inline ostream&amp;operator&lt;&lt;(ostream&amp; os,const vector&lt;T&gt;&amp; v){string delim="[";for(unsigned int i=0;i &lt; v.size();i++){os&lt;&lt;delim&lt;&lt;v[i];delim=", ";}return os&lt;&lt;"]";} template&lt;typename T&gt;inline ostream&amp;operator&lt;&lt;(ostream&amp; os,const set&lt;T&gt;&amp; v){string delim="[";for (typename set&lt;T&gt;::const_iterator ii=v.begin();ii!=v.end();++ii){os&lt;&lt;delim&lt;&lt;*ii;delim=", ";}return os&lt;&lt;"]";} template&lt;typename T1,typename T2&gt;inline ostream&amp;operator&lt;&lt;(ostream&amp; os,const map&lt;T1,T2&gt;&amp; v){string delim="[";for (typename map&lt;T1,T2&gt;::const_iterator ii=v.begin();ii!=v.end();++ii){os&lt;&lt;delim&lt;&lt;*ii;delim=", ";}return os&lt;&lt;"]";} // CUT end class Vehicle { public: int n; Vehicle(int n):n(n){cout&lt;&lt;"Ctor Vehicle "&lt;&lt;n&lt;&lt;endl;} Vehicle(Vehicle&amp; v):n(v.n){cout&lt;&lt;"Copy Ctor Vehicle "&lt;&lt;n&lt;&lt;endl;} virtual ~Vehicle(){cout&lt;&lt;"Dtor Vehicle "&lt;&lt;n&lt;&lt;endl;} virtual ostream&amp; dump(ostream&amp; os){return os&lt;&lt;"Vehicle("&lt;&lt;n&lt;&lt;")";} string to_str(){stringstream s; dump(s); return s.str();} virtual Vehicle&amp; operator++(){n++;return *this;} virtual Vehicle operator++(int x){Vehicle v(*this); operator++(); return v;} }; class Car: public Vehicle { public: Car(int n): Vehicle(n){cout&lt;&lt;"Ctor Car "&lt;&lt;n&lt;&lt;endl;} virtual ~Car(){cout&lt;&lt;"Dtor Car "&lt;&lt;n&lt;&lt;endl;} virtual ostream&amp; dump(ostream&amp; os){return os&lt;&lt;"Car("&lt;&lt;n&lt;&lt;")";} virtual Car operator++(int x){Car v(*this); operator++(); return v;} /* data */ }; ostream&amp; operator&lt;&lt;(ostream&amp; os, Vehicle&amp; v) { return v.dump(os); } int main(int argc, char const *argv[]) { Vehicle * v = new Car(10); // cout&lt;&lt;c++&lt;&lt;endl; // cout&lt;&lt;c&lt;&lt;endl; return 0; } </code></pre> <p>I get the following error with gcc:</p> <pre><code>C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:16:0: warning: "debug" redefined [enabled by default] C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:13:0: note: this is the location of the previous definition C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:14: error: invalid covariant return type for 'virtual Car Car::operator++(int)' C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:35:18: error: overriding 'virtual Vehicle Vehicle::operator++(int)' C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp: In member function 'virtual Car Car::operator++(int)': C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:57: error: no matching function for call to 'Car::operator++()' C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:57: note: candidate is: C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:14: note: virtual Car Car::operator++(int) C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:14: note: candidate expects 1 argument, 0 provided </code></pre> <p>How do I get <code>++</code> operators for both <code>Car</code> and <code>Vehicle</code> with minimum number of virtual overrides?</p>
 

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