屏蔽并提取C中的位 [英] Mask and extract bits in C

问题描述

我一直在寻找有关遮罩的帖子，但仍然无法理解如何从C中的数字中提取某些位.

I've been looking at posts about mask but still can't get my head around how to extract certain bits from a number in C.

假设我们有一个int number 0001 1010 0100 1011，那么它的十六进制表示形式是x1a4b对吗?如果我想知道第5到第7个数字(在这种情况下为101)，我应该使用int mask= 0x0000 1110 0000 0000, int extract = mask&number吗?

Say if we have a int number 0001 1010 0100 1011 , so it's hex representation is x1a4b right? If I want to know the 5th to 7th number, which is 101 in this case, shall I use int mask= 0x0000 1110 0000 0000, int extract = mask&number?

我又如何检查它是否为101?我想==在这里不起作用...非常感谢！

Also how can I check if it is 101? I guess == won't work here... Many thanks!

推荐答案

假定gcc扩展0b定义二进制文字:

Assuming the gcc extension 0b to define binary literals:

int number = 0b0001101001001011; /* 0x1a4b */
int mask =   0b0000111000000000; /* 0x0e00 */
/* &'ed:     0b0000101000000000;    0x0a00 */
int extract = mask & number;     /* 0x0a00 */

if (extract == 0b0000101000000000)
/* or if 0b is not available:
if (extract == 0x0a00 ) */
{
  /* success */
}
else
{
  /* failure */
}

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