如何检查我的字节标志，以验证特定位是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诸如10101010之类的标志，并且我想知道如何验证特定位在1或0上.

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

以下是可用于测试任何所需位的函数:

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;
}

一些解释:

左移运算符(<<)用于创建位掩码. (1< 0)等于00000001，(1<< 1)等于00000010，(1<< 3)等于00001000，依此类推.因此，移位0个测试最右边的位. 31的移位将是32位值的最左位.

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，将两侧的所有位都设置为1.示例:1111& 0001 = 0001; 1111& 0010 == 0010; 0000& 0001 =0000.因此，表达式(value&(1<< bitindex))如果关联的位的值为1，则将返回位掩码，如果关联的位为0，则将返回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. (实际上可以将其排除在外，但我想明确指出.)

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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