ReDim sizes or resizes a dynamic array at runtime. With Preserve the existing values are kept, but only the last dimension can change.

Code

ReDim Preserve names(1 To n)

• Size at runtime

  Dim names() As String ReDim names(1 To n) → An array sized to n after n is known

  Dynamic sizing.

• Grow with Preserve

  ReDim Preserve names(1 To n + 1) → One more slot, values kept

  Growing a list.

• Two dimensions

  ReDim Preserve data(1 To 10, 1 To cols + 1) → Only the last dimension can grow with Preserve

  The 2D limitation.

• ReDim Preserve in a loop is slow; size once to the maximum, or use a Collection.
• ReDim without Preserve clears the array.
• Erase releases the memory.

• Preserve cannot change the first dimension of a 2D array; transpose your layout.
• ReDim on a fixed-size array is a compile error.