Removing bitwise flags

Question

How would i remove flags from my enum

I can add them easy with m_Buttons | (button);

enum WindowButton
{
    None = 0,

    Minimize = (1 << 0),
    Maximize = (1 << 1),
    Close = (1 << 2),
};
inline WindowButton operator|(WindowButton a, WindowButton b)
{
    return static_cast<WindowButton>(static_cast<int>(a) | static_cast<int>(b));
}
inline WindowButton& operator |= (WindowButton& lhs, WindowButton rhs)
{
    return lhs = static_cast<WindowButton>(static_cast<WindowButton>(lhs) | static_cast<WindowButton>(rhs));
}

This is the function where im trying to add / remove

void Window::SetButton(WindowButton button, bool show)
{
    if (show)
        m_Buttons |= (button);
    else
        m_Buttons | ~(button); // This is not working to remove flags
}

Using `|` instead of `|=` means `m_Buttons` isn't going to be modified... but `|=` wouldn't be right either. — , Apr 16 '17 at 10:40
Hint: Turning a bitflag on `flags |= f`. Turning a bitflag off: `flags &= ~f`. — Nik Bougalis, Apr 16 '17 at 10:40

score 4 · Answer 1 · edited Apr 16 '17 at 10:42

4

m_Buttons | ~(button); // This is not working to remove flags

Of course not. It sets where it should clear, and then throws away the result. Should be

m_Buttons &= ~button;

NB parentheses are redundant here.

edited Apr 16 '17 at 10:42

Peter Hall

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answered Apr 16 '17 at 10:40

user207421

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'&=': no operator found which takes a left-hand operand of type – xuzisijuya Apr 16 '17 at 10:45
1

@xuzisijuya So define `&=` the same way you defined `|=`, except using `&`. – Apr 16 '17 at 10:51
1

@xuzisijuya (And I'd almost forget, `operator~` as well.) – Apr 16 '17 at 10:56
@hvd still getting the same errors – xuzisijuya Apr 16 '17 at 10:59
Of type *what*? What type have you defined `m_buttons` as? Should be `int` or `long`. – user207421 Apr 16 '17 at 11:51
@EJP `m_Buttons` is defined as `WindowButton` – xuzisijuya Apr 16 '17 at 13:10
@xuzisijuya Well that's wrong. WindowButton can only have the values enumerated within it. Or else *define* that operator, just as you've defined the others. – user207421 Apr 17 '17 at 00:40

Removing bitwise flags

1 Answers1