在WM_KEYDOWN消息中获取lParam参数的第30位 [英] Get 30th bit of the lParam param in WM_KEYDOWN message

问题描述

我需要获取通过WM_KEYDOWN消息传递的lParam参数的第30位。此位写入此处允许我知道键是否被按下。这个代码是否正确？

 （lParam>> 30）& 1 
  

解决方案

lParam& 0x40000000 。如果这不是零，那么设置 b30 （我认为三十二的三十个位，顺便说一句）。更有可能是 {logical-and，compare} 操作，而不是 {shift，logical-and，compare} （lParam），你也可以使用一个合适的编译器生成更高效的代码。 >> 30）& 1 但为什么要承担风险？

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

解决方案

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?

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