C inheritance from multiple base classes with the same virtual function name

I tried this code:

class A
{
 virtual void foo() = 0;
}; 

class B
{
 virtual void foo() = 0;
};

class C: public A, public B
{
 //virtual void A::foo(){} 
 //virtual void B::foo(){}

 virtual void A::foo();
 virtual void B::foo();
 };

void C::A::foo(){}
void C::B::foo(){}

int main() 
{
 C c;
 return 0;
}

It is ok when using the comment section, but when I try to write the definition outside the class declaration, The compiler will report an error.
I am using the MSVC11 compiler, does anyone know how to write this?
I need to move the code to the cpp file.

Thank you~~

The function overrides the base class according to the name and parameter type (See below). Therefore, your class C has two virtual functions foo, one inherits from each of A and B. But the function void C :: foo() will cover both:

[class.virtual] / 2

If a virtual member function vf is declared in a class Base and in a class Derived, derived directly or indirectly from Base, a member function vf with the same name, parameter-type-list, cv-qualification, and ref-qualifier (or absence of same) as Base::vf is declared, then Derived::vf is also virtual (whether or not it is so declared) and it overrides Base::vf.

As I am commenting As already mentioned in [dcl.meaning]/1, it is prohibited to use qualified-id in the declaration of (member) functions:

When the declarator-id is qualified, the declaration shall refer to a previously declared member of the class or namespace to which the qualifier refers […]”

Therefore any virtual void X ::foo(); as C internal The declaration is illegal.

Code

class C: public A, public B
{
 virtual void foo() ;
};

is AFAIK the only way to overwrite foo, it will overwrite A::foo and B::foo. For A::foo and B::foo, except for introducing another Outside the inheritance layer, there is no way to cover it in two different ways:

#include 

struct A
{ 
 virtual void foo() = 0;
};

struct B
{
 virtual void foo() = 0;
} ;

struct CA: A
{
 virtual void foo() {std::cout << "A" << std::endl; }
} ;

struct CB: B
{
 virtual void foo() {std::cout << "B" << std::endl; }
} ;

struct C: CA, CB {};

int main() {
 C c;
 //c.foo(); // ambiguous

 A& a = c;
 a.foo();

 B& b = c;
 b.foo();< br />}