virtual method of header give errors during g++ compilation - c++

Question

I'm initiating to C++ and I'm struggling with a compiling problem
I have a source file "binomial.cpp" in which I define the methods of my classes :
#include "binomial.hpp"
using namespace std;
int Bernoulli::operator()(){
return (rand() < p*RAND_MAX) ? a : b;
};
int Binomial::operator()(){
int result(0);
for(int i(0);i<n;++i){
int a;
a = B();
result += a;
};
return result;
};
and a header file "binomial.hpp" where I declare all my classes :
#include <iostream>
#ifndef BINOMIAL
#define BINOMIAL
class RandVar {
virtual int operator()() =0;
};
struct Bernoulli : public RandVar {
Bernoulli(int a = -1,int b = 1, double p = 0.5) : a(a), b(b), p(p) {};
int operator()(){};
private:
int a,b;
double p;
};
class Binomial : public RandVar {
public:
Binomial(Bernoulli B, int n=2)
: B(B), n(n) {}
int operator()(){};
private:
Bernoulli B;
int n;
};
#endif
But when I try to compile that through g++ using the command : g++ -Wall binomial.cpp -o binomial those errors occur :
binomial.hpp: In member function ‘virtual int Bernoulli::operator()()’:
binomial.hpp:14:19: warning: no return statement in function returning non-void [-Wreturn-type]
int operator()(){};
^
binomial.hpp: In member function ‘virtual int Binomial::operator()()’:
binomial.hpp:26:19: warning: no return statement in function returning non-void [-Wreturn-type]
int operator()(){};
^
binomial.cpp: At global scope:
binomial.cpp:4:5: error: redefinition of ‘int Bernoulli::operator()()’
int Bernoulli::operator()(){
^~~~~~~~~
In file included from binomial.cpp:2:0:
binomial.hpp:14:6: note: ‘virtual int Bernoulli::operator()()’ previously defined here
int operator()(){};
^~~~~~~~
binomial.cpp:8:5: error: redefinition of ‘int Binomial::operator()()’
int Binomial::operator()(){
^~~~~~~~
In file included from binomial.cpp:2:0:
binomial.hpp:26:6: note: ‘virtual int Binomial::operator()()’ previously defined here
int operator()(){};
^~~~~~~~
I don't really know how to fix that so if someone can take some time to help a beginner it would be great !

Answer 1

You should replace both
int operator()(){};
with
int operator()();
in the header files. You meant to provide declarations, not definitions. To provide just a declaration (not provide the code right away), just drop the {}.