View Full Version : Simple dynamic UDT-subarrays

24-10-2014, 14:11
This is a very simple tutorial script at beginner level

How to append different length dynamic subarrays to some udt
using heap-memory and virtual variables or layovers.

It is meant for fixed size-elements of any type - so no dynamic string-arrays.
(but with a little effort you can create a DWord-array to store pointers for each "string")

This example stores some different sized arrays of Long-variables and shows how to access them again.
To clearify that this Long is just a placeholder for any fixed-size variable or udt it's aliased as "someType"

uses only built-in functions but needs 1.9.8 for the Redim-fix on virtual variables.

Uses "Console"

' this just to make the example better readeable:
Alias Long As someType

Type t_Type ' whatever udt, don't care
' it's just an example-type

' myArray() As someType is sadly not possible
' but we can help it...

pArray As DWord ' here node a dynamic array of some type
' "pArray As DWord" here equals pointer of "myArray() As someType"

End Type

Dim foo(3) As t_Type ' have an array of t_Type...
' but ".myArray()" shall be something different to each,
' maybe an array of someType in this example
' each different number of elements

Function TBMain()
Dim i, j As Long ' some counters

PrintL $CRLF & "different length sub-arrays example:" & $CRLF

' -- creating the data:

' a virtual array As datatype At ( now allocated space ) and fill in data

Local myArray(5) As someType At HEAP_Alloc(5 * SizeOf(someType)) Value = 1,2,3,4,5

' store pointer in foo(1).pArray using GetAt

foo(1).pArray = GetAt(myArray)

' done with foo(1)...

' now re-use myArray() for the next members of foo and

' redim it new size At now allocated space...

ReDim myArray(7) At HEAP_Alloc(7* SizeOf(someType))

' VarPtr to FIRST element of myArray equals GetAT

foo(2).pArray = VarPtr(myArray(1))

' fill in some data

Array Assign myArray = -1,-2,-3,-4,-5,-6,-7

' finally do the same to foo(3).pArray but another way:

' store pointer of allocated space for 8 elements of someType

foo(3).pArray = HEAP_Alloc(8 * SizeOf(someType))

' Redim myArray(8) At allocated space

ReDim myArray(8) At foo(3).pArray

' fill in members data one by one this time:

For i = 1 To UBound(myArray)
myArray(i) = i * i

' -- retrieving the data:

' go through all of foo()

For i = 1 To UBound(foo)

PrintL "foo(" & i & ").myArray :"

' place virtual array in correct size upon allocated heap:

ReDim myArray(HEAP_Size(foo(i).pArray)/SizeOf(someType)) At foo(i).pArray

' now can access it:

PrintL Str$(UBound(myArray)) & " elements:"

' print out each array-member:

For j = 1 To UBound(myArray)
Print myArray(j) & $TAB

PrintL $CRLF & "--------------------------" & $CRLF

PrintL "-------------------------> key to continue"

' now how is this dynamic?

' want to add 1 more element to foo(1)-array...

foo(1).pArray = HEAP_Realloc(foo(1).pArray, HEAP_Size(foo(1).pArray) + SizeOf(someType) * 1 )

ReDim myArray(HEAP_Size(foo(1).pArray)/SizeOf(someType)) At foo(1).pArray

' set new value to last element of "foo(1).myArray()"
myArray(UBound(myArray)) = 123

' see if the old ones are still there:
For j = 1 To UBound(myArray)
Print myArray(j) & $TAB

PrintL $CRLF & "-------------------------> key to end"

End Function

' allocated heap gets freed by thinBasic if script ends