How to: Change the Size of an Array

Artigo
11/18/2006

You resize an array variable by assigning a new array object to it. You can use either a standard assignment statement or the ReDim Statement (Visual Basic). In either case, the original array is replaced with a completely new one, and the array variable points to the new array.

Resizing an array helps you manage memory efficiently. For example, you can start with a small array and then increase its size if you need more elements. Alternatively, you can start with a large array and then reduce its size when you no longer need all of it. This technique takes up the additional memory only when you need it.

To resize an array variable using a standard assignment statement

Create the new array object, specifying the new dimension lengths.

Assign the new array object to the array variable.

Dim thisArrayVariable() As Integer = New Integer(99) {}
thisArrayVariable = New Integer(49) {}

To resize an array variable using the ReDim statement

Specify the new dimension lengths for the array variable in the ReDim statement.

Dim thisArrayVariable() As Integer = New Integer(99) {}
ReDim thisArrayVariable(9)

When you ReDim an array, the existing values of its elements are normally lost. However, you can retain them by including the Preserve keyword in the ReDim statement.

To resize an array variable preserving existing element values

Specify the new dimension lengths for the array variable in the ReDim statement.
Add the Preserve keyword in the ReDim statement. The following example creates a new array, initializes its elements from the corresponding elements of the existing array in arrayToIncrease, and assigns the new array to the array variable arrayToIncrease.
```
Dim arrayToIncrease(9, 49)
ReDim Preserve arrayToIncrease(9, 199)
```

If you use Preserve on a multidimensional array, you can change only the last dimension length. If you attempt to change any of the other dimensions, an ArrayTypeMismatchException exception occurs.

If you resize a large array using the Preserve keyword, keep in mind that Visual Basic must copy all the existing elements into the new array. This can make your performance slower.

Compartilhar via

How to: Change the Size of an Array

To resize an array variable using a standard assignment statement

To resize an array variable using the ReDim statement

To resize an array variable preserving existing element values

See Also

Tasks

Concepts

Other Resources

Recursos adicionais