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c++winapiwindows-messagesbit-shift

Get 30th bit of the lParam param in WM_KEYDOWN message

I need to get the 30th bit of the lParam param passed with the WM_KEYDOWN message. This bit as written here allows me to know if the key was pressed before. Is this code right to get it?

(lParam >> 30) & 1
Solution

  • I would just use lParam & 0x40000000. If that's non-zero, then b30 was set (I consider that the thirty first bit of the thirty two, by the way). And there's more likelihood that it will be a {logical-and, compare} operation rather than {shift, logical-and, compare}.

    Mind you, there's a good chance that a decent compiler would generate the more efficient code anyway even if you used (lParam >> 30) & 1 but why take the risk?