删除前16个字节? [英] Remove First 16 Bytes?

问题描述

如何从字节数组中删除多个字节?

How would I go about removing a number of bytes from a byte array?

推荐答案

正如nobugz的评论(和Reed Copsey的回答)所提到的，如果您实际上不需要将结果作为字节数组，则应考虑使用 ArraySegment<T> :

As nobugz's comment (and Reed Copsey's answer) mentions, if you don't actually need the result as a byte array, you should look into using ArraySegment<T>:

ArraySegment<byte> segment = new ArraySegment<byte>(full, 16, full.Length - 16);

否则，将需要复制-数组始终具有固定大小，因此您不能从现有数组中删除"前16个字节.取而代之的是，您必须创建一个较小的新数组，并将相关数据复制到其中.

Otherwise, copying will be necessary - arrays always have a fixed size, so you can't "remove" the first 16 bytes from the existing array. Instead, you'll have to create a new, smaller array and copy the relevant data into it.

对于非LINQ方法，Zach的建议是正确的，但是可以使它更简单(假设您已经知道原始数组的长度至少为16个字节):

Zach's suggestion is along the right lines for the non-LINQ approach, but it can be made simpler (this assumes you already know the original array is at least 16 bytes long):

byte[] newArray = new byte[oldArray.Length - 16];
Buffer.BlockCopy(oldArray, 16, newArray, 0, newArray.Length);

或

byte[] newArray = new byte[oldArray.Length - 16];
Array.Copy(oldArray, 16, newArray, 0, newArray.Length);

我可疑 Buffer.BlockCopy会稍快一些，但我不确定.

I suspect Buffer.BlockCopy will be slightly faster, but I don't know for sure.

请注意，如果涉及的数组很大，则这两种方法都可能比LINQ方法效率更高:LINQ方法要求每个字节都从迭代器中分别返回，并可能要进行中间复制(以相同的方式)因为将项目添加到List<T>需要定期增长后备阵列).显然，不要进行微优化，但是如果这部分代码是性能瓶颈，则值得检查.

Note that both of these could be significantly more efficient than the LINQ approach if the arrays involved are big: the LINQ approach requires each byte to be individually returned from an iterator, and potentially intermediate copies to be made (in the same way as adding items to a List<T> needs to grow the backing array periodically). Obviously don't micro-optimise, but it's worth checking if this bit of code is a performance bottleneck.

我对这三种方法进行了非常快速而肮脏的"基准测试.我不相信基准可以区分Buffer.BlockCopy和Array.Copy-它们非常接近-但是LINQ方法慢了100倍以上.

I ran a very "quick and dirty" benchmark of the three approaches. I don't trust the benchmark to distinguish between Buffer.BlockCopy and Array.Copy - they were pretty close - but the LINQ approach was over 100 times slower.

在我的笔记本电脑上，使用10,000个元素的字节数组，用LINQ花了近10秒钟执行了40,000个拷贝；上述方法完成相同数量的工作大约需要80毫秒.我将迭代次数增加到4,000,000，但仍然只花了大约7秒钟.显然，适用于微基准测试的一般警告，但这是一个相当大的差异.

On my laptop, using byte arrays of 10,000 elements, it took nearly 10 seconds to perform 40,000 copies using LINQ; the above approaches took about 80ms to do the same amount of work. I upped the iteration count to 4,000,000 and it still only took about 7 seconds. Obviously the normal caveats around micro-benchmarks apply, but this is a pretty significat difference.

如果这在对性能很重要的代码路径中，请绝对使用上述方法:

Definitely use the above approach if this is in a code path which is important to performance :)

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