按位运算比较结果错误

Question

我一定是哪里做错了：我有这个枚举

enum OperetionFlags
{
        NONE = 0x01,
        TOUCHED = 0x02,
        MOVE_RIGHT = 0x04,
        MOVE_LEFT = 0x08,
        GAME_START = 0x10,
        GAME_END = 0x20
};

int curentState ;

我的程序没有启动，我设置了：

main()
{
    curentState = 0 

    if (( curentState & GAME_START) == 0)
    {
        curentState |= GAME_START;
    }

    if ((curentState & MOVE_RIGHT) == 0)
    {
        curentState |= TOUCHED & MOVE_RIGHT;
    }

    if (curentState & GAME_START)
    {
        if (curentState & TOUCHED & MOVE_RIGHT) // HERE IS WHERE IT FAILED
        {

        }
    }

}

curentState & TOUCHED & MOVE_RIGHT 即使我将 TOUCHED & MOVE_RIGHT 位设置为 on

也是错误的

Answer 1

尝试

 curentState |= TOUCHED | MOVE_RIGHT;

Answer 2

对于按位运算，|类似于按位加法，&类似于按位乘法（如果有进位则丢弃进位）。
（很容易认为a & b是"the one bits from a and the one bits from b"，其实是"the bits that are one in both a and b"。）

让我们跟随：

curentState = 0 

    curentState is 00000000

if (( curentState & GAME_START) == 0)
{
    curentState |= GAME_START;
}

    curentState is now 00010000

if ((curentState & MOVE_RIGHT) == 0)
{
    curentState |= TOUCHED & MOVE_RIGHT;

        TOUCHED & MOVE_RIGHT is 00000000
        so curentState is still 00010000
}

if (curentState & GAME_START)
{
        curentState & TOUCHED is 00010000 & 00000010 = 00000000
        and 00000000 & MOVE_RIGHT is 00000000      

    if (curentState & TOUCHED & MOVE_RIGHT) // HERE IS WHERE IT FAILED
    {
    }
}

如果你想设置两个位，你需要使用|； TOUCHED | MOVE_RIGHT.

如果你想测试两个位，你需要非常冗长：

(curentState & (TOUCHED | MOVE_RIGHT)) == (TOUCHED | MOVE_RIGHT)

或者用逻辑 and

单独测试它们

(curentState & TOUCHED) && (curentState & MOVE_RIGHT)

按位运算比较结果错误

Bitwise operation compare result is wrong

c++

bit-manipulation

bitwise-operators