Redim

Home › Array Functions › ReDim

ReDim

Creates or resizes a variable-length array; elements are reset unless Preserve is used.

Syntax

Declaring a Dynamic Array:
ReDim [ Shared ] symbolname([subscript [, ...]]) As datatype [, ...]
ReDim [ Shared ] As datatype symbolname([subscript [, ...]]) [, ...]
Resizing a Dynamic Array:
ReDim [ Preserve ] symbolname([subscript [, ...]]) [, ...]
or:
ReDim [ Preserve ] [ ( ] expression [ ) ] ([subscript [, ...]]) [, ...]

Parameters

• symbolname
• expression
• (expression)
• subscript
• lowerbound To ] upperbound

Description

ReDim can be used to define new variable-length arrays, or resize existing variable-length arrays while keeping the same number of dimensions. ReDim always produces variable-length arrays, so, unlike Dim, variable-length arrays can be defined with constant subscripts.

When defining a new variable-length array, its elements are default constructed. For simple data types like Integer or Double, the elements are initialized to zero (0). For user-defined types with a default constructor, that will be called.

When used with in a user-defined type, ReDim creates variable-length arrays while being able to pre-size them with constant subscripts.

NOTES:

Remarks

Differences from QB

• Preserve was in Visual Basic, but not in QBASIC.
• Multi-dimensional arrays in FreeBASIC are in row-major order, rather than column-major order.

See also

• Common
• Dim
• Erase
• Extern
• LBound
• Preserve
• Shared
• Static
• UBound
• Var

Examples

'' Define a variable-length array with 5 elements

ReDim array(0 To 4) As Integer

For index As Integer = LBound(array) To UBound(array)

    array(index) = index

Next

'' Resize a variable-length array with 10 elements

'' (the lower bound should be kept the same)

ReDim Preserve array(0 To 9)

Print "index", "value"

For index As Integer = LBound(array) To UBound(array)

    Print index, array(index)

Next

This program will produce the following output:

index         value
 0             0
 1             1
 2             2
 3             3
 4             4
 5             0
 6             0
 7             0
 8             0
 9             0

'' Define a variable-length array

Dim array() As Integer

'' ReDim array to have 3*4 elements

ReDim array(1 To 3, 1 To 4)

Dim As Integer n = 1, i, j

Print "3 * 4:"

Print

For i = LBound(array, 1) To UBound(array, 1)

    For j = LBound(array, 2) To UBound(array, 2)

        array(i, j) = n

        Print Using "##  "; array(i, j);

        n += 1

    Next

    Print

Next

Print

'' ReDim Preserve array to have 4*4 elements, preserving the contents

'' (only the first upper bound should be changed)

ReDim Preserve array(1 To 4, 1 To 4)

Print "4 * 4:"

Print

For i = LBound(array, 1) To UBound(array, 1)

    For j = LBound(array, 2) To UBound(array, 2)

        Print Using "##  "; array(i, j);

    Next

    Print

Next

Print

'' ReDim Preserve array to have 2*4 elements, preserving but trancating the contents

'' (only the first upper bound should be changed)

ReDim Preserve array(1 To 2, 1 To 4)

Print "2 * 4:"

Print

For i = LBound(array, 1) To UBound(array, 1)

    For j = LBound(array, 2) To UBound(array, 2)

        Print Using "##  "; array(i, j);

    Next

    Print

Next

Print

This program will produce the following output:

3 * 4:

 1   2   3   4
 5   6   7   8
 9  10  11  12

4 * 4:

 1   2   3   4
 5   6   7   8
 9  10  11  12
 0   0   0   0

2 * 4:

 1   2   3   4
 5   6   7   8

'' Define a variable-length array as UDT field

Type UDT

   Dim As Integer array(Any)

End Type

Dim As UDT u(0 To 3)

'' For use of Redim with a complex array expression

'' (especially if the array expression itself contains parentheses),

'' the array expression must be enclosed in parentheses

'' in order to solve the parsing ambiguity:

''    Redim u(0).array(0 To 9)

''    induces error 4: Duplicated definition, u in 'Redim u(0).array(0 To 9)'

ReDim (u(0).array)(0 To 9)

---

Category: Array Functions
Kind: keyword

---

Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.