如何在C中获取无符号8位类型的最高有效位

Question

I'm trying to get the most significant bit of an unsigned 8-bit type in C.

This is what I'm trying to do right now:

uint8_t *var = ...;
...
(*var >> 6) & 1

Is this right? If it's not, what would be?

Answer 1

要从uint8_t指针指向的存储器中获取最高有效位，您需要移位7位。

(*var >> 7) & 1

Answer 2

The most standard/correct way of masking bits is to use a readable bit mask of the form 1u << bit . Any C programmer spotting 1u << n in code will know that it is a bit mask - so it is self-documenting code.

So if you want bit number 7, you would write

*var & (1u << 7)

The u suffix is important for rugged code, since you want to avoid accidental implicit promotions to signed types.

Answer 3

另一种选择是简单地应用位掩码并检查结果值：

*var & 0x80u // 1000 0000