Redim an array by pointer?

[Edwin Knoppert]

I would like to use a pointer to redim an array like this test code:

Type xxttt
    h As Long
    Moreparams1 as long
    Moreparams2 as long
End Type

Function Test2( ByRef x As xxttt ) As Long

    Dim h() As Long At x.h
    ReDim Preserve h( 0 To 100 )

End Function

Function Test() As Long

    Dim h( 0 To 0 ) As Local Long
    Dim x As xxttt
    x.h = VarPtr( h() )    
    Test2( x )

    MsgBox Str$( UBound( h ) )

End Function

Usually i am using alternative code but i would like to do it this way if possible.

[Chris Holbrook]

I don't think so, but you could put the UBOUND of the array into the first element when you DIM it?

BTW PRESERVE is not needed with DIM/REDIM AT.

[Michael Mattias]

>BTW PRESERVE is not needed with DIM/REDIM AT

More like, it has no meaning. When absolute arrays are used, the programmer is 100% responsible for the management of the underlying memory.

Should probably be a compile-time error, "PRESERVE Option not allowed with DIM/REDIM 'AT' "

Actually it should be a "warning only" but the compiler does not do warnings.. compilation has a binary solution set : pass/fail. But warning messages would be really cool.

Edwin, if you want to REDIM an array in a procedure, just pass the whole array...

   REDIM   Z(0) 
   CALL    SizeMyArray (Z(), other params) 

FUNCTION SizeMyArray (X() AS something, other params) 
   REDIM [PRESERVE] X (value based on params) 
END FUNCTION

MCM

[Edwin Knoppert]

In fact it was for a callback.
I had luck with BYREF as String so i thought a pointer to an array would do as well.
I think it is possible but maybe not with dim at.

Don't know..

[Michael Mattias]

Edwin I can't see what you are trying to accomplish with your function.

If you want to resize the array in a separate procedure, just pass it...

FUNCTION Test2 (X() AS something) 
     REDIM X(100) 
END FUNCTION 
....

LOCAL h() AS LONG

 REDIM h( 0 To 0 )    ' just use REDIM, compiler can be weird with DIM
 Test2( h() )

  Print LBOUND and ubound of h() here, they will be 0 and 100.

MCM

[Erich Schulman]

Actually it should be a "warning only" but the compiler does not do warnings.. compilation has a binary solution set : pass/fail. But warning messages would be really cool.
[/code]
MCM

*puts on a Red Hat*
There are quite a few things I can think of that should have warnings, and warning messages doesn't exclude a pass/fail result. (Though I would prefer an exit code of 0-255 where 0 is full success and 1-255 represent any kind of compile/link/resource/whatever problems.) There should also be warning options (think of http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html ) I would also like to see a pragma to "escape" a single warning.

[Gösta H. Lovgren-2]

Edwin I can't see what you are trying to accomplish with your function.

If you want to resize the array in a separate procedure, just pass it...

Is what he wants to accomplish really important here? I mean, Edwin asked if An array could be redimmed using a pointer? Obviously he knows there are other ways to do it. After all, he is Edwin Knoppert, quite clearly neither a newby nor PB dummy.

It seems to me the appropriate responses would be one (or combination) of "Yes, Eddie, and here's how ...", or "No Edwin, and here's why ..." or "Gee, Mr. Knoppert, I really don't know but could it be maybe done this way ...".

[Edwin Knoppert]

I want to pass it to enumwindows() api for example.
A string's varptr can be passed and in the callback obtained byref directly.
This way i can reset the length or contents of the string fine.
Though i am not able to do that using a type var.
The type var is passed the same but the array's varptr resides in the type var and is not passed as lparam.

[Michael Mattias]

>Edwin asked if An array could be redimmed using a pointer?

The answer is "yes," if that pointer is to the array descriptor.

Then he pointed out ...
>I want to pass it to enumwindows() api for example

So, you pass the address of the array descriptor by defining your callback function thus....

FUNCTION CallbackProc (BYVAL Hwnd AS LONG, X() AS SomeType) AS LONG

... and calling the Enum function with your lparam/dwUser value = VARPTR(Array()) (with the empty parens)


No muss, no fuss, no bother.

MCM

[John Gleason]

It can be done, but you haven't allocated the necessary memory (and PB doesn't allocate it in DIM AT), it may GPF.

#COMPILE EXE
#DIM ALL

TYPE xxttt
    h AS LONG
    Moreparams1 AS LONG
    Moreparams2 AS LONG
END TYPE

FUNCTION PBMAIN () AS LONG

    DIM h( 0 ) AS LOCAL LONG    'dimension to max needed size, eg. here it would need to be h(100)
    DIM x AS xxttt
    x.h = VARPTR( h() )
    Test2( x, h() )             'If the array h() is not passed, Test2 creates a 2nd different array entirely.
    
    ? STR$(h(0))
    ? STR$(h(1))                'unallocated memory, possible GPF. To solve problem, dimension h() above to
    ? STR$(h(100))              'the max needed size, eg. 100
    MSGBOX STR$( UBOUND( h ) )

END FUNCTION

FUNCTION Test2( BYREF x AS xxttt, h() AS LONG ) AS LONG

'   Dim h() As Long At x.h
'   REDIM PRESERVE h( 0 TO 100 ) AS LONG    '<this will no longer be at x.h
'   So to keep the array at x.h, the above can be done in one statement:
    REDIM h( 0 TO 100 ) AS LONG AT x.h 'this will however, be dimensioning into unallocated memory. Could GPF.

END FUNCTION

[Eros Olmi]

What about some dynamic string fake buffers and some dummy DIM ... AT ?
Graet flexibility, great power.

Type xxttt
  MyArray1 As Long
  MyArray2 As Long
  '...
End Type
Function Allocate_My_X( ByRef x As xxttt ) As Long
  '---Allocate room for 100 LONG: 100 * sizeof(LONG)
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray1)
  DummyString(1&) = Repeat$(100 * 4, $Nul)
  
  ReDim DummyLong(1& To 100&) As Long At VarPtr(x.MyArray1)
  '---Do whatever with DummyLong
  
  '---Allocate room for 100 EXT: 100 * sizeof(EXT)
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray2)
  DummyString(1&) = Repeat$(100 * 10, $Nul)
  ReDim DummyExt(1& To 100&) As Ext At VarPtr(x.MyArray2)
  '---Do whatever with DummyLong
End Function
Function Free_My_X( ByRef x As xxttt ) As Long
  '---Remove
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray1)
  Reset DummyString(1&)
  
  '---Remove
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray2)
  Reset DummyString(1&)
End Function
Function ReDim_My_X( ByRef x As xxttt ) As Long
  
  '---Add 150 LONG numbers
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray1)
  DummyString(1&) += Repeat$(150 * 4, $Nul)
  
  '---Add 350 EXT number
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray2)
  DummyString(1&) += Repeat$(350 * 10, $Nul)
End Function
Function Use_My_X( ByRef x As xxttt ) As Long 
  Local nItems As Long
  
  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray1)
  nItems = Len(DummyString(1&))/4
  ReDim DummyLong(1& To nItems) As Long At VarPtr(x.MyArray1)
  '---Do whatever with DummyLong
  MsgBox "My array of LONGs has" & Str$(UBound(DummyLong)) & " elements"
    

  ReDim DummyString(1& To 1&) As String At VarPtr(x.MyArray2)
  nItems = Len(DummyString(1&))/10
  ReDim DummyExt(1& To nItems) As Ext At VarPtr(x.MyArray2)
  '---Do whatever with DummyLong
  MsgBox "My array of EXTs has" & Str$(UBound(DummyExt)) & " elements"
End Function

Function PBMain() As Long
    Dim x As xxttt
    Allocate_My_X ( x )
    Use_My_X      ( x )
    MsgBox "Now making some redim ..."
    ReDim_My_X    ( X )
    Use_My_X      ( x )
    Free_My_X     ( x )
End Function

[Michael Mattias]

Call me set in my ways, but setting up the callback to have a parameter of "MyArray() AS MyType" sure seems the easiest way.

When you do this you may use any array functions you want - including REDIM [PRESERVE] - without doing anything else anywhere.

[Edwin Knoppert]

Haven't you seen the other params?!!

[Michael Mattias]

>Haven't you seen the other params?!!

Code not shown.

You said you wanted to pass the array to EnumWIndows and REDIM it there. I did that.

You want more params, pass 'em as additional members of MyArray().

Or, I suppose you can contact my office for a quotation.

[Edwin Knoppert]

Gee, can't find the terminate thread button..