Swap bytes within an byte array

Question

Does anyone know if there's a .NET function to swap bytes within an Byte Array?

For example, lets say I have a byte array with the following values:

byte[] arr = new byte[4];

[3] 192
[2] 168
[1] 1
[0] 4

I want to swap them so that the array becomes:

[3] 168
[2] 192
[1] 4
[0] 1

Val of [3] was swapped with val of [2] and val of [1] with val of [0]

I'm not aware of anything. Chances are you'll just need to write yourself a helper function that takes an array and two indexes to swap (as Jon shows below). — GEEF
– GEEF, Commented Jun 25, 2014 at 16:34
@VP. I feel that a comment essentially instructing the OP to continue reading this page is somewhat redundant. — Jonathon Reinhart
– Jonathon Reinhart, Commented Jun 25, 2014 at 16:39
When I had originally posted the comment, you had not yet posted the answer, so the comment just said 'go ahead and roll your own'. However, after I saw you post that immediately thereafter, I figured I should mention there now exists an example further down the page. — GEEF
– GEEF, Commented Jun 25, 2014 at 16:42
@VP. Understood. That happens to me all the time; I would have just deleted the comment. — Jonathon Reinhart
– Jonathon Reinhart, Commented Jun 25, 2014 at 16:44

Jonathon Reinhart · Accepted Answer · 2014-06-25 16:40:27Z

6

How about this extension method:

public static class ExtensionMethods
{
    /// <summary>Swaps two bytes in a byte array</summary>
    /// <param name="buf">The array in which elements are to be swapped</param>
    /// <param name="i">The index of the first element to be swapped</param>
    /// <param name="j">The index of the second element to be swapped</param>
    public static void SwapBytes(this byte[] buf, int i, int j)
    {
        byte temp = buf[i];
        buf[i] = buf[j];
        buf[j] = temp;
    }
}

Usage:

class Program
{
    void ExampleUsage()
    {
        var buf = new byte[] {4, 1, 168, 192};
        buf.SwapBytes(0, 1);
        buf.SwapBytes(2, 3);
    }
}

edited Jun 25, 2014 at 16:40

answered Jun 25, 2014 at 16:34

Jonathon Reinhart

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1 Comment

Eric Bergman Over a year ago

Thanks for the example, I created a method similar to this one but making it an extension is a nice addition, thanks for the help, I thought maybe there was already one defined in .NET.

Nicholas Carey · Accepted Answer · 2014-06-25 17:36:12Z

0

I sounds like you want to swap byte pairs in-place across the entire array. You could do something like this, process the array from left to right:

public static void SwapPairsL2R( this byte[] a )
{
  for ( int i = 0 ; i < a.Length ; i+=2 )
  {
    int t  = a[i]   ;
    a[i]   = a[i+1] ;
    a[i+1] = a[i]   ;
    a[i]   = t      ;
   }
   return ;
}

Swapping right-left wouldn't be much different.

answered Jun 25, 2014 at 17:36

Nicholas Carey

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