[RESOLVED] Mod array

[hitesh 2000]

hello i want to add elements in a byte array at the Begin of an array confuse any help

[.paul.]

try this:

Dim b1() As Byte = {&H4, &H5, &H6}
Dim b2() As Byte = {&H1, &H2, &H3}
Dim b3() As Byte = b2.Concat(b1).ToArray

[dunfiddlin]

You can't. You'll need to create a new array combining an array of the new elements and the original array, so ...

Dim CombinedArray() As Byte = NewElementsArray.Concat(OriginalByteArray)

[Shaggy Hiker]

You will need to create a new array, as noted, and there are a variety of ways to do that. The older way, making use of Array.Copy, is not quite as easy to read as what dunfiddlin showed, but I tested it out a while back, and Array.Copy is considerably faster than the alternatives. I think it uses some low level memory management code to perform a fast copy under the hood, though I'm not sure about that.

[hitesh 2000]

Thanks everyone

[dbasnett]

You will need to create a new array, as noted, and there are a variety of ways to do that. The older way, making use of Array.Copy, is not quite as easy to read as what dunfiddlin showed, but I tested it out a while back, and Array.Copy is considerably faster than the alternatives. I think it uses some low level memory management code to perform a fast copy under the hood, though I'm not sure about that.

I'd say it is faster! So much so that if this code was intended for a high use area of the application I would NOT use concat.

        Const alen As Integer = 99999
        Dim a1(alen) As Byte
        Dim a2(alen) As Byte

        'some data
        'For x As Integer = 1 To a1.Length - 1
        '    a1(x) = CByte(x And &HFE) 'note mask
        'Next
        a1(0) = &HFF 'set start of this array
        Array.Copy(a1, a2, a2.Length) 'copy a1 to a2
        a2(1) = &HFF 'a2 starts with FF FF

        Dim stpw As New Stopwatch
        Const tries As Integer = 10
        Dim c12() As Byte = New Byte() {}
        Dim li As Integer

        'use array copies to get combined array
        stpw.Restart()
        For x As Integer = 1 To tries
            Array.Resize(c12, 0) 'set size of destination
            Array.Resize(c12, a1.Length + a2.Length) 'set size of destination
            Array.Copy(a1, c12, a1.Length) 'copy a1 to combined
            Array.Copy(a2, 0, c12, a1.Length, a2.Length) 'copy a2 to combined
        Next
        stpw.Stop()
        Debug.WriteLine(stpw.Elapsed.TotalMilliseconds.ToString("n3"))

        li = Array.LastIndexOf(c12, CByte(&HFF)) 'show ffff
        Debug.WriteLine("{0}{1}  {2}", Convert.ToString(c12(li - 1), 16), Convert.ToString(c12(li), 16), li.ToString("n0"))
        Debug.WriteLine("")

        Array.Resize(c12, 0) 'set size of destination
        stpw.Restart()
        For x As Integer = 1 To tries
            c12 = a1.Concat(a2).ToArray '<<<<<<<<<<<< using concat
        Next
        stpw.Stop()
        Debug.WriteLine(stpw.Elapsed.TotalMilliseconds.ToString("n3"))

        li = Array.LastIndexOf(c12, CByte(&HFF)) 'show ffff
        Debug.WriteLine("{0}{1}  {2}", Convert.ToString(c12(li - 1), 16), Convert.ToString(c12(li), 16), li.ToString("n0"))
        Debug.WriteLine("")

edit: I created a function to combine arrays using Array.Copy, and using it the code was still much faster(50x) than concat.