如何在 .NET 中的较大集合中定位值序列（特别是字节）

发布于 2024-08-22 23:38:22 字数 318 浏览 7 评论 0原文

我需要解析文件中的字节，以便仅在识别出特定的字节序列后才获取数据。例如，如果序列只是 0xFF（一个字节），那么我可以在集合上使用 LINQ：

byte[] allBytes = new byte[] {0x00, 0xFF, 0x01};
var importantBytes = allBytes.SkipWhile(byte b => b != 0xFF);
// importantBytes = {0xFF, 0x01}

但是有没有一种优雅的方法来检测多字节序列 - 例如 0xFF、0xFF - 特别是在它开始时回溯的方法获得误报匹配？

原文

I need to parse the bytes from a file so that I only take the data after a certain sequence of bytes has been identified. For example, if the sequence is simply 0xFF (one byte), then I can use LINQ on the collection:

byte[] allBytes = new byte[] {0x00, 0xFF, 0x01};
var importantBytes = allBytes.SkipWhile(byte b => b != 0xFF);
// importantBytes = {0xFF, 0x01}

But is there an elegant way to detect a multi-byte sequence - e.g. 0xFF, 0xFF - especially one that backtracks in case it starts to get a false positive match?

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你好，陌生人 2024-08-29 23:38:22

我不知道任何内置的方式；像往常一样，您始终可以编写自己的扩展方法。这是我的想法（可能有更有效的方法来实现它）：

public static IEnumerable<T> AfterSequence<T>(this IEnumerable<T> source,
    T[] sequence)
{
    bool sequenceFound = false;
    Queue<T> currentSequence = new Queue<T>(sequence.Length);
    foreach (T item in source)
    {
        if (sequenceFound)
        {
            yield return item;
        }
        else
        {
            currentSequence.Enqueue(item);

            if (currentSequence.Count < sequence.Length)
                continue;

            if (currentSequence.Count > sequence.Length)
                currentSequence.Dequeue();

            if (currentSequence.SequenceEqual(sequence))
                sequenceFound = true;
        }
    }
}

我必须检查以确保这是正确的，但它应该为您提供基本的想法；迭代元素，跟踪检索到的最后一个值序列，找到序列时设置一个标志，设置标志后，开始返回每个后续元素。

编辑-我确实运行了测试，它确实工作正常。这是一些测试代码：

static void Main(string[] args)
{
    byte[] data = new byte[]
    {
        0x01, 0x02, 0x03, 0x04, 0x05,
        0xFF, 0xFE, 0xFD, 0xFC, 0xFB, 0xFA
    };
    byte[] sequence = new byte[] { 0x02, 0x03, 0x04, 0x05 };
    foreach (byte b in data.AfterSequence(sequence))
    {
        Console.WriteLine(b);
    }
    Console.ReadLine();
}

I'm not aware of any built-in way; as per usual, you can always write your own extension method. Here's one off the top of my head (there may be more efficient ways to implement it):

public static IEnumerable<T> AfterSequence<T>(this IEnumerable<T> source,
    T[] sequence)
{
    bool sequenceFound = false;
    Queue<T> currentSequence = new Queue<T>(sequence.Length);
    foreach (T item in source)
    {
        if (sequenceFound)
        {
            yield return item;
        }
        else
        {
            currentSequence.Enqueue(item);

            if (currentSequence.Count < sequence.Length)
                continue;

            if (currentSequence.Count > sequence.Length)
                currentSequence.Dequeue();

            if (currentSequence.SequenceEqual(sequence))
                sequenceFound = true;
        }
    }
}

I'll have to check to make sure that this is correct, but it should give you the basic idea; iterate through the elements, track the last sequence of values retrieved, set a flag when the sequence is found, and once the flag is set, start returning each subsequent element.

Edit - I did run a test, and it does work correctly. Here's some test code:

static void Main(string[] args)
{
    byte[] data = new byte[]
    {
        0x01, 0x02, 0x03, 0x04, 0x05,
        0xFF, 0xFE, 0xFD, 0xFC, 0xFB, 0xFA
    };
    byte[] sequence = new byte[] { 0x02, 0x03, 0x04, 0x05 };
    foreach (byte b in data.AfterSequence(sequence))
    {
        Console.WriteLine(b);
    }
    Console.ReadLine();
}

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