c - bool 代数 NOT 和 DWORD - 建议修复

Question

这个问题已经有答案了:

How can I remove a flag in C? (3 个回答)

How to set, clear, and toggle a single bit? (27 个回答)

已关闭 5 年前。

我发现一些遗留代码在设置文件属性时出错。它看起来像这样 -

flag1 = 0x0001;
flag2 = 0x0002;

DWORD flags = flag1 | flag2;

//great - flags is 3

DWORD prevValue  = 0x0010; //say

//add our new flags to prevValue
DWORD newVal = prevValue | flags;

//newVal is 19

//but now I want to remove those flags from newVal

DWORD backToPrev = newVal & !flags;

//but according to my compiler (vs2012)
//!flags is 0, it can't do the logical NOT on the DWORD

ASSERT (backToPrev); // it's 0, should be 16

有什么修复建议吗？

Answer 1

! 运算符是逻辑 NOT。该运算符的结果是 0 或 1。您想要的是按位 NOT 运算符 ~:

DWORD backToPrev = newVal & ~flags;