Preserve with ReDim

Each time you execute the ReDim statement, all the values currently stored in the array are lost. Visual Basic resets the values to the Empty value (for Variant arrays), to zero (for numeric arrays), to a zero-length string (for string arrays), or to Nothing (for arrays of objects).

This is useful when you want to prepare the array for new data, or when you want to shrink the size of the array to take up minimal memory. Sometimes you may want to change the size of the array without losing the data in the array. You can do this by using ReDim with the Preserve keyword. For example, you can enlarge an array by one element without losing the values of the existing elements using the UBound function to refer to the upper bound:

ReDim Preserve DynArray(UBound(DynArray) + 1)

Only the upper bound of the last dimension in a multidimensional array can be changed when you use the Preserve keyword; if you change any of the other dimensions, or the lower bound of the last dimension, a run-time error occurs. Thus, you can use code like this:

ReDim Preserve Matrix(10, UBound(Matrix, 2) + 1)

But you cannot use this code:

ReDim Preserve Matrix(UBound(Matrix, 1) + 1, 10)

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James Crowley James first started this website when learning Visual Basic back in 1999 whilst studying his GCSEs. The site grew steadily over the years while being run as a hobby - to a regular monthly audience ...


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