C语言 c 获取整数的第 n 个字节
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c get nth byte of integer
提问by Kamran224
I know you can get the first byte by using
我知道你可以通过使用获得第一个字节
int x = number & ((1<<8)-1);
or
或者
int x = number & 0xFF;
But I don't know how to get the nth byte of an integer. For example, 1234 is 00000000 00000000 00000100 11010010 as 32bit integer How can I get all of those bytes? first one would be 210, second would be 4 and the last two would be 0.
但我不知道如何获取整数的第 n 个字节。例如，1234 是 00000000 00000000 00000100 11010010 作为 32 位整数 我怎样才能得到所有这些字节？第一个是 210，第二个是 4，最后两个是 0。
回答by Vaughn Cato
int x = (number >> (8*n)) & 0xff;
where n is 0 for the first byte, 1 for the second byte, etc.
其中 n 为第一个字节为 0，第二个字节为 1，依此类推。
回答by Dmitri
For the (n+1)th byte in whatever order they appear in memory (which is also least- to most- significant on little-endian machines like x86):
对于它们出现在内存中的任何顺序的第 (n+1) 个字节（这在像 x86 这样的小端机器上也是最低到最高的）：
int x = ((unsigned char *)(&number))[n];
For the (n+1)th byte from least to most significant on big-endian machines:
对于 big-endian 机器上从最低到最高有效的第 (n+1) 个字节：
int x = ((unsigned char *)(&number))[sizeof(int) - 1 - n];
For the (n+1)th byte from least to most significant (any endian):
对于从最低到最高有效（任何字节序）的第 (n+1) 个字节：
int x = ((unsigned int)number >> (n << 3)) & 0xff;
Of course, these all assume that n< sizeof(int), and that numberis an int.
当然，这些都假设n< sizeof(int)，那number就是int.
回答by akappa
int nth = (number >> (n * 8)) & 0xFF;
int nth = (number >> (n * 8)) & 0xFF;
Carry it into the lowest byte and take it in the "familiar" manner.
将其放入最低字节并以“熟悉”的方式取出。
回答by David Fletcher
If you are wanting a byte, wouldn't the better solution be:
如果你想要一个字节，更好的解决方案不是：
byte x = (byte)(number >> (8 * n));
byte x = (byte)(number >> (8 * n));
This way, you are returning and dealing with a byte instead of an int, so we are using less memory, and we don't have to do the binary and operation & 0xffjust to mask the result down to a byte. I also saw that the person asking the question used an int in their example, but that doesn't make it right.
这样，您将返回并处理一个字节而不是一个 int，因此我们使用的内存更少，而且我们不必执行二进制和操作& 0xff只是为了将结果屏蔽为一个字节。我还看到提出问题的人在他们的示例中使用了 int ，但这并不正确。
I know this question was asked a long time ago, but I just ran into this problem, and I think that this is a better solution regardless.
我知道很久以前就有人问过这个问题，但我刚刚遇到了这个问题，我认为无论如何这是一个更好的解决方案。
