Nested class' function: implementation code

[Robertlzw]

Hi C++ folks,

I can implement a function inside a nested class as follows:

class A {
  struct B {
   void f() { //impl code here; }
  };
};

or with this:

class A {
  struct B {
   void f(); // declaration only
  };
};

struct A::B {  
   void f() { //impl code here; }
};

But I got a compilation error if I try this:

class A {
  struct B {
   void f(); // declaration only
  };
};

void A::B::f() { //impl code here; } // compilation error 

How can I get rid of the compilation error of the third approach?

[hamsterman]

The third one works fine for me (except the commented '}' )
What error are you getting?

But the second one fails. And it should. Struct redefinition is not allowed.

[Robertlzw]

Sorry for the confusion with my original sample code. I got it (the issue is with the return type):

class A {
  struct C;  // defined later
  struct B {
   C f(); // declaration only
  };
};

instead of:

C A::B::f() { //impl code here; } // compilation error 

It should be:

B::C  A::B::f() { //impl code here; } // return type: B::C 

BWT( @hamsterman): the second one should be:

class A {
   struct B;
};

struct A::B { // imp code here }; 

[Disch]

C is not part of B, it's part of A

therefore it should be:

A::C A::B::f()
{
 // ...
}

[Robertlzw]

A typo.It should be:

A::C  A::B::f() { //impl code here; } // return type: A::C  

[Disch]

That's correct (except for the commented out closing brace, which you seem to keep doing in your examples)

So... what's the problem? What compilation error are you getting?

[Robertlzw]

The problem solved. To summarize:

class A {
  struct C;  // defined later
  struct B {
   C f(); // declaration only
  };
};

I got an compilation error "return type is not defined" when I used:

C A::B::f() { // impl } 

The correct one should be:

A::C A::B::f() { // impl }