Passing multidimensional array to a function?

[Mike Joseph]

Hmm... i thought i read in another post that to pass a
multidimensional array, you simply enter the number
of dimensions in array in the Function declaration.

e.g.
Declare Function Pass2(test(2) as long) as long

But this does not seem to be allowed. How does one pass
a multidimensional array to a function?

-Mike
p.s. In a future version, id really like to see Types that
can hold real array and not just "tables."


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[Lance Edmonds]

That is the technique employed in PB/DOS. In PB/CC and PB/DLL, you just pass the array descriptor -- that is, you leave the parentheses empty.

Regarding real arrays within UDT's... you can easily do this by using DIM..AT to dim an aray over the top of the array member of the UDT. You still cannot use dynamic (variable-length) strings this way though, as they are not valid UDT members.



------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Mike Joseph]

Thanks. Passing the multidimensioanl array works. Can you show
me an example of using Dim AT with an array in a UDT?

If i have
Type Test
t(1 to 20) as long
End Type

and subsequently i fill the values of t()
and then later want to dim a local variable
as a LONG array, at the location of Test.t()
can that be done without overwriting the contents
of Test.t() ? I want to preserve the values already
in test.t() and use the local array to reference
it. Possible?

Thanks
-Mike

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[Mike Joseph]

I guess my confusion is, how do i Dim AT an "array" member
of a UDT if it has no descriptor? It seems incorrect to
DIM AT the first element of that UDT array member, but thats
the only thing that seems to work.

#COMPILE EXE
#DIM ALL
DECLARE FUNCTION Pass(lp AS LONG ptr) AS LONG

TYPE TEST
   x(0 TO 2) AS LONG
END TYPE

FUNCTION PBMAIN() AS LONG
   DIM tt AS TEST
   DIM lp AS LONG PTR

   tt.x(0) = 100
   tt.x(1) = 200
   tt.x(2) = 300
   lp = VARPTR(tt.x())  ' <-- Doesnt Work and if
                        '     I try using tt.x(0) then
                        '     that will result in the
                        '    local array in the following 
                        '    function to not be aligned properly
   
END FUNCTION

FUNCTION Pass (lp AS LONG PTR) AS LONG
   DIM t() AS LONG AT lp
   
   REDIM PRESERVE t(0 TO 2)
  
   MSGBOX "T.X(0) = " & STR$(t(0)) & " T.X(1) = " & STR$(t(1))
END FUNCTION

I hope this explanation makes sense. Is what im trying to
do possible? Otherwise using Dim AT doesnt seem like its
much use when working with "arrays" in UDTs.

-Mike


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[Lance Edmonds]

DIM..AT does not initialize the memory, it simply "maps" an array over the top of the existing memory.

#COMPILE EXE
 
TYPE a
  b(1 TO 100) AS LONG
END TYPE
 
FUNCTION PBMAIN
    DIM z AS a
    z.b(75) = RND(1,100)
    DIM y(1:100) AS LONG AT VARPTR(z.b(1))
    ARRAY SORT y(), DESCEND
    MSGBOX STR$(y(1))
END FUNCTION

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Mike Joseph]

Excellent. Thanks. That works just the way i need it.
-Mike

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[Lance Edmonds]

uh,uh... since you are using DIM..AT, you cannot use REDIM PRESERVE... that would effectively move the memory (arrays almost always "move" during a REDIM). Since DIM..AT does not "own" the memory, you cannot move it this way... since the UDT member array is a fixed size (determined at compile time), you must limit your DIM..AT array to within the constraints of the member array size. If you want to resize your DIM..AT array, use REDIM..AT.

For example:

#COMPILE EXE

TYPE a
  b(1 TO 100) AS LONG
END TYPE

FUNCTION PBMAIN
    DIM z AS a
    z.b(75) = RND(1,100)
    DIM y(1:100) AS LONG AT VARPTR(z.b(1))
    ARRAY SORT y(), DESCEND
    MSGBOX STR$(y(1)) + STR$(z.b(1))
    REDIM y(1:50) AS LONG AT VARPTR(z.b(50))
    z.b(75) = RND(1,100)
    ARRAY SORT y(), DESCEND
    MSGBOX STR$(y(1)) + STR$(z.b(50))
END FUNCTION

Essentially, DIM..AT is a powerful way of creating a psuedo-union with an array. However, if you want a truly dynamic and expandable array, use a normal array to start with.



------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>