Forward declaring an enum in C++?

Question

I'm trying to do something like the following: enum E; void Foo(E e); enum E {A, B, C}; which the compiler rejects. I've had a quick look on Google and the consensus seems to be "you can't do it", but I can't understand why. Can anyone explain? Clarification 2: I'm doing this as I have private methods in a class that take said enum, and I do not want the enum's values exposed - so, for example, I do not want anyone to know that E is defined as enum E { FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X } as project X is not something I want my users to know about. So, I wanted to forward declare the enum so I could put the private methods in the header file, declare the enum internally in the cpp, and distribute the built library file and header to people. As for the compiler - it's GCC.

Answer 1

//Declares and defines the enum in the private section of the class

using namespace std;

#include <iostream>

class test

{

private:

typedef enum _TEnumFunctionality

{

FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X

} TEnumFunctionality;

TEnumFunctionality projectX;

public:

test ( int x)

{

// sets the enum based on the value of x

switch (x)

{

case 0: { projectX = FUNCTIONALITY_NORMAL;

break;

}

case 1: {

projectX = FUNCTIONALITY_RESTRICTED;

break;

}

case 2:

{

projectX = FUNCTIONALITY_FOR_PROJECT_X;

}

} //switch

} //constructor

GetProjX() { return(projectX); }

};

int main()

{

test T(1);

test t(0);

test X(2);

cout << T.GetProjX( ) << endl;

cout << t.GetProjX( ) << endl;

cout << X.GetProjX( ) << endl;

}