Bitmask as member enum with default parameter

Question

I can't figure out how to implement a bitmask parameter for my class.

Specifically my CreateMenuDlg function

I've searched google quite a bit, finding all sorts of forum questions that ask about bitmasks, bitfields, etc. and everyone posts minimal example code
I keep finding people using #define but that wouldn't work for my class since I need to call it from main dialog with something like this:

DialogMenu *p_dlgMenu = new DialogMenu( this, &p_dlgMenu, this );
p_dlgMenu->CreateMenuDlg( ( DialogMenu::CLOSES | DialogMenu::WINDOW_HANDLER ), DialogMenu::DLG_CHECKOUT );

Here's my code:

class DialogMenu : public CDialog
{
    DECLARE_DYNAMIC(DialogMenu)

public:
    enum dlgFlags
    {
        HIDES = 2^0,
        CLOSES = (2^0)+1,
        WINDOW_HANDLER = 2^1,
        MSG_HANDLER = (2^1)+1,
        DLG_SHOPPING_MENU = 2^2,
        DLG_DYNAMIC_MENU = (2^2)+1,
    };

    dlgFlags operator|=( dlgFlags first, flgFlags second)
    {
        return (dlgFlags)( (unsigned)first | (unsigned)second );
    }

    enum dlgType { DLG_CHECKOUT, DLG_INVENTORY_EDIT, DLG_SHIPPING_RECEIVING };

    DialogMenu( CDialog * const, DialogMenu ** const, CWnd* pParent = NULL );
    void PostNcDestroy();
    virtual ~DialogMenu();

    void CreateMenuDlg( dlgFlags paramFlags = ( CLOSES | MSG_HANDLER | DLG_DYNAMIC_MENU ), dlgType paramType = DLG_CHECKOUT );

protected:
    virtual void DoDataExchange(CDataExchange * pDX);

    CDialog * m_parent;
    DialogMenu ** m_self;  
};

For which I'm receiving errors from my bitmask enumeration not being int.

dialogmenu.h(21): error C2440: 'default argument' : cannot convert from 'int' to 'DialogMenu::dlgFlags'
Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast)

But my OR operator overload should be taking care of that cast!

If I have to I'll abandon bitflags altogether, but I'm trying to get the hang of them and I get more points on my project per C++ subject covered and bitfields was the most recent thing we learned. (Although we never learned how to implement them as enumerations, only playing with them on character variables.)

Doesn't applying the recommended cast from the error message fix your problem? — πάντα ῥεῖ, Nov 27 '14 at 09:09
How do I do that? Cast it directly in the default parameter? I need users of this class (my group-mates) to be able to use the function with just DialogMenu::CLOSES and not have to cast it each time they call the function. — Numerials, Nov 27 '14 at 09:14
Awh thats what was wrong with it. I didn't know that I just knew it wasn't coming out correctly so I had to go change it to Hides = 0, Closes = 1, Window_Handler = 0, Msg_Handler = 2, Dlg_Shop = 0, Dlg_Dynamic = 4 — Numerials, Nov 27 '14 at 18:23

score 1 · Accepted Answer · answered Nov 27 '14 at 09:19

This is not an OR operator for enum dlgFlags, instead it's an operator|= for DialogMenu (having 3 operands including *this, so it doesn't compile):

dlgFlags operator|=( dlgFlags first, flgFlags second)
{
    return (dlgFlags)( (unsigned)first | (unsigned)second );
}

Change it to

friend dlgFlags operator|(dlgFlags first, dlgFlags second)
{
    return (dlgFlags)( (unsigned)first | (unsigned)second );
}

friend keyword is needed to make it not a member of DialogMenu. Personally I'd prefer to move it out of the DialogMenu class together with enum dlgFlags itself:

enum dlgFlags
{
    HIDES = 2^0,
    // ...
};

dlgFlags operator|(dlgFlags first, dlgFlags second)
{
    return (dlgFlags)( (unsigned)first | (unsigned)second );
}

class DialogMenu : public CDialog
{
     // ...
}

This one worked!
Just had to add DialogMenu:: scope for the casting after return.

Only reason I want it to stay inside class is because I'm trying to emulate fstream's ios::open, which is the instruction given by our instructor, so I need scope resolution to use class DialogMenu.
Thanks! — Numerials, Nov 27 '14 at 09:24

score 0 · Answer 2 · answered Nov 27 '14 at 09:21

0

Use an explicit cast for each value within the enum declaration itself.

answered Nov 27 '14 at 09:21

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Bitmask as member enum with default parameter

2 Answers2