如何检查我的字节标志，验证特定位是 1 还是 0? [英] How can I check my byte flag, verifying that a specific bit is at 1 or 0?

问题描述

我使用一个字节来存储像 10101010 这样的标志，我想知道如何验证特定位是在 1 还是 0.

I use a byte to store some flag like 10101010, and I would like to know how to verify that a specific bit is at 1 or 0.

推荐答案

这里有一个函数可以用来测试任何需要的位:

Here's a function that can be used to test any desired bit:

bool is_bit_set(unsigned value, unsigned bitindex)
{
    return (value & (1 << bitindex)) != 0;
}

一点解释:

左移运算符 (<<) 用于创建位掩码.(1 <<0) 将等于 00000001，(1 <<1) 将等于 00000010，(1 <<3) 将等于 00001000，等等.所以 0 测试的移位最右边的位.31 的移位将是 32 位值的最左边的位.

The left shift operator (<<) is used to create a bit mask. (1 << 0) will be equal to 00000001, (1 << 1) will be equal to 00000010, (1 << 3) will be equal to 00001000, etc. So a shift of 0 tests the rightmost bit. A shift of 31 would be the leftmost bit of a 32-bit value.

按位与运算符 (&) 给出的结果是两边的所有位都为 1.示例:1111 &0001 = 0001；1111&0010 == 0010;0000 &0001 = 0000.因此，表达式 (value & (1 << bitindex)) 如果关联位的值是 1，则返回位掩码，如果关联位为 0，则返回 0.

The bitwise-and operator (&) gives a result where all the bits that are 1 on both sides are set. Examples: 1111 & 0001 = 0001; 1111 & 0010 == 0010; 0000 & 0001 = 0000. So, the expression (value & (1 << bitindex)) will return the bitmask if the associated bit is 1 in value, or will return 0 if the associated bit is 0.

最后，我们只检查结果是否为非零.(这实际上可以省略，但我喜欢明确说明.)

Finally, we just check whether the result is non-zero. (This could actually be left out, but I like to make it explicit.)

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