VBA (Excel) Initialize Entire Array without Looping

Question

This is easy, at least if you want a 1-based, 1D or 2D variant array:

Sub StuffVArr()
    Dim v() As Variant
    Dim q() As Variant
    v = Evaluate("=IF(ISERROR(A1:K1), 13, 13)")
    q = Evaluate("=IF(ISERROR(A1:G48), 13, 13)")
End Sub

Byte arrays also aren’t too bad:

Private Declare Sub FillMemory Lib "kernel32" Alias "RtlFillMemory" _
        (dest As Any, ByVal size As Long, ByVal fill As Byte)

Sub StuffBArr()
    Dim i(0 To 39) As Byte
    Dim j(1 To 2, 5 To 29, 2 To 6) As Byte
    FillMemory i(0), 40, 13
    FillMemory j(1, 5, 2), 2 * 25 * 5, 13
End Sub

You can use the same method to fill arrays of other numeric data types, but you’re limited to only values which can be represented with a single repeating byte:

Sub StuffNArrs()
    Dim i(0 To 4) As Long
    Dim j(0 To 4) As Integer
    Dim u(0 To 4) As Currency
    Dim f(0 To 4) As Single
    Dim g(0 To 4) As Double

    FillMemory i(0), 5 * LenB(i(0)), &HFF 'gives -1
    FillMemory i(0), 5 * LenB(i(0)), &H80 'gives -2139062144
    FillMemory i(0), 5 * LenB(i(0)), &H7F 'gives 2139062143

    FillMemory j(0), 5 * LenB(j(0)), &HFF 'gives -1

    FillMemory u(0), 5 * LenB(u(0)), &HFF 'gives -0.0001

    FillMemory f(0), 5 * LenB(f(0)), &HFF 'gives -1.#QNAN
    FillMemory f(0), 5 * LenB(f(0)), &H80 'gives -1.18e-38
    FillMemory f(0), 5 * LenB(f(0)), &H7F 'gives 3.40e+38

    FillMemory g(0), 5 * LenB(g(0)), &HFF 'gives -1.#QNAN
End Sub

If you want to avoid a loop in other situations, it gets even hairier. Not really worth it unless your array is 50K entries or larger. Just set each value in a loop and you’ll be fast enough, as I talked about in an earlier answer.

Leave a Comment Cancel reply