How do I use low-level 8 bit flags as conditionals?

In my keyboard hook, each keypress gets a flag that states if it was injected or not. http://msdn.microsoft.com/en-us/library/ms644967(VS.85).aspx

I've distilled a KBDLLHOOKSTRUCT from the lParam. I can access kbd.flags.XXX. I just don't know how to convert this 8bit flag into an if (injected) {... type conditional 开发者_开发百科that I know how to use.

If one of you smart computer-science types would help me out I'd really appreciate it.

    private static IntPtr HookCallback(int nCode, IntPtr wParam, IntPtr lParam)
    {
        KBDLLHOOKSTRUCT kbd = new KBDLLHOOKSTRUCT();
        Marshal.PtrToStructure(lParam, kbd);

        //if (injected) {...

Cheers!

.NET supports this with the [Flags] attribute:

[Flags]
enum KbdHookFlags {
  Extended = 0x01,
  Injected = 0x10,
  AltPressed = 0x20,
  Released = 0x80
}

Sample usage:

  KBDLLHOOKSTRUCT info = (KBDLLHOOKSTRUCT)Marshal.PtrToStructure(lParam, typeof(KBDLLHOOKSTRUCT));
  if ((info.flags & KbdHookFlags.Released) == KbdHookFlags.Released) {
    // Key was released
    // etc..
  }

You need to bitwise-and it with a mask. For example, the injected bit is bit 4. That's binary 00010000, hex 0x10. So you bitwise-and it with 0x10, and see if anything's left:

bool isInjected = ((kbd.flags & 0x10) != 0);

(Of course, as per Andrew's answer, it would be a good idea to define a LLKHF_INJECTED constant for this rather than including the hex value directly in your code!)

Use the bitwise AND operator to check if the relevant bit is set in the flags variable:

if (kbd.flags & LLKHF_INJECTED)
{
    ...
}

You need to check that the bitflag is set. Easy to do with bitwise operations. The documentation states that bit four is used for the injected flag, bit 4 (or 5 if you count the first bit as 1) equals 16, so you can do a bitwise AND against the flag.

if ((kbd.flags & 16) == 16)
{
    FireTorpedoes();
}

You can learn more about bitwise operations here:

• Bitwise operation and usage
• http://en.wikipedia.org/wiki/Bitwise_operation
• http://en.wikipedia.org/wiki/Mask_(computing)

The reason everyone is saying to use a bitwise & and then compare to zero or the flag:

  0111 1000        // kbd.flags 
& 0001 0000        // Injected
          =
  0001 0000        // (!= 0 or ==Injected)