测试是否在 DWORD 标志中设置了特定位

Question

我有一个 DWORD 变量，我想测试其中是否设置了特定位。我的代码如下，但我不确定我是否从 win32 数据类型 KBDLLHOOKSTRUCT 传输位我的 lparam 数据类型正确吗？

请参阅记录 DWORD 标志变量的 MSDN：http://msdn.microsoft.com/en-us/library/ms644967(v=vs.85).aspx

union KeyState 
{
    LPARAM lparam;      

    struct     
    {         
        unsigned nRepeatCount : 16;         
        unsigned nScanCode    : 8;         
        unsigned nExtended    : 1;         
        unsigned nReserved    : 4;         
        unsigned nContext     : 1;         
        unsigned nPrev        : 1;         
        unsigned nTrans       : 1;     
    }; 
}; 


KBDLLHOOKSTRUCT keyInfo = *((KBDLLHOOKSTRUCT*)lParam);
KeyState myParam;
myParam.nRepeatCount    = 1;
myParam.nScanCode       = keyInfo.scanCode;
myParam.nExtended       = keyInfo.flags && LLKHF_EXTENDED; // maybe it should be keyInfo.flags & LLKHF_EXTENDED or keyInfo.flags >> LLKHF_EXTENDED
myParam.nReserved       = 0;        
myParam.nContext        = keyInfo.flags && LLKHF_ALTDOWN;     
myParam.nPrev           = 0; // can store the last key pressed as virtual key/code, then check against this one, if its the same then set this to 1 else do 0   
myParam.nTrans          = keyInfo.flags && LLKHF_UP;


// Or maybe I shd do this to transfer bits...
myParam.nRepeatCount    = 1;
myParam.nScanCode       = keyInfo.scanCode;
myParam.nExtended       = keyInfo.flags & 0x01;
myParam.nReserved       = (keyInfo.flags >> 0x01) & (1<<3)-1;      
myParam.nContext        = keyInfo.flags & 0x05;     
myParam.nPrev           = 0;       // can store the last key pressed as virtual key/code, then check against this one, if its the same then set this to 1 else do 0   
myParam.nTrans          = keyInfo.flags & 0x07;

Answer 1

而不是

myParam.nExtended = keyInfo.flags && LLKHF_EXTENDED

你需要

myParam.nExtended = (keyInfo.flags & LLKHF_EXTENDED) != 0;

它是& 而不是&&，因为您需要位与而不是逻辑与。 !=0 确保答案是 0 或 1（而不是 0 或其他非零值），因此它可以在您的一位位域中表示。

Answer 2

CheckBits(DWORD var, DWORD mask)
{
    DWORD setbits=var&mask; //Find all bits are set
    DWORD diffbits=setbits^mask; //Find all set bits that differ from mask
    return diffbits!=0; //Retrun True if all specific bits in variable are set
}

Answer 3

如果你想合并两个位，你会使用 | (bitwise OR) 运算符：

myParam.nExtended = keyInfo.flags | LLKHF_EXTENDED;

myParam.nExtended = keyInfo.flags | 0x01;

要检查是否设置了位，您可以使用 &（按位与）运算符：

if(myParam.nExtended & LLKHF_EXTENDED) ...