C++ polymorphism, overloading and inheritance

Question

Given

#include <iostream>
#include <string>

using std::cout;
using std::endl;

class A
{
public:
    virtual int a() const = 0;
    virtual int a(const int i) const = 0;
};

class B : public A
{
public:
    virtual int a() const { return A::a(0); }    
};

class C : public B
{
public:
    virtual int a(const int i) const { return i; }
};


int main()
{
    C c;
    cout << c.a() << endl;
    cout << c.a(1) << endl; 
}

I did not tests with different compilers but i have the following errors:

main.cpp:31:17: error: no matching function for call to ‘C::a()’
     cout << c.a() << endl;
                 ^
main.cpp:24:17: note: candidate: virtual int C::a(int) const
     virtual int a(const int i) const { return i; }
                 ^
main.cpp:24:17: note:   candidate expects 1 argument, 0 provided

I do not understand really why, I was expecting that class C can access at B::a() .

It seems that is resolving the Ca() as Ca(int) . Basically the virtual method from B is not visible. Anyone knows why?

EDIT

The idea is something like: A as "interface", B as "abstract class", C the "concrete class"

SOLUTION

What i was trying to achieve is possible with using A::a using B::a and changing the B::a() call from A::a(0) to a(0) .

Like the example here provided by songyuanyao

Answer 1

C::a hides B::a . When the name a is found at the scope of class C , name lookup stops, further scopes including class B won't be checked.

name lookup examines the scopes as described below, until it finds at least one declaration of any kind, at which time the lookup stops and no further scopes are examined.

You can add using to introduce B::a into C 's scope.

class C : public B
{
public:
    using B::a;
    virtual int a(const int i) const { return i; }
};