ARRAY POINTER

[Joe Speroni]

The following program does not compile correctly because
I'm trying to pass the pointer of an array to a function
instead of the array itself. Is there a syntax that will
accomplish this?
------------------------------------------------------------
#COMPILE EXE
#REGISTER NONE
#INCLUDE "Win32Api.Inc"

FUNCTION ShowS3(x() AS STRING) AS LONG
MSGBOX X(3)
END FUNCTION

FUNCTION PBMAIN()
DIM S(1:10) AS STRING:FOR i&=1 TO 10:S(i&)=STR$(100+i&):NEXT
SPtr&=VARPTR(S())
'ShowS3 S() ' works fine, but how to pass a pointer instead?
ShowS3 SPtr&
END FUNCTION

[LRantanen]

Joe,

if you want to pass to sub the pointer to an string array and an index to this array, you have to do e.g. following

FUNCTION ShowS3(x AS STRING PTR, idx AS INTEGER) AS LONG
   LOCAL i AS INTEGER
   
   FOR i = 0 TO idx - 2
       INCR x
   NEXT

   MSGBOX @X

END FUNCTION

FUNCTION PBMain
    DIM S(1:10) AS STRING
    DIM SPtr AS STRING PTR
    
    FOR i&=1 TO 10
        S(i&)=STR$(100+i&)
    NEXT
    
    SPtr=VARPTR(S(1))
    ShowS3 BYVAL SPtr, 3
END FUNCTION

or if you dont have to pass the index as argument, do following

FUNCTION ShowS3(x AS STRING PTR) AS LONGINCR x

   MSGBOX @X

END FUNCTION

FUNCTION PBMain
    DIM S(1:10) AS STRING
    DIM SPtr AS STRING PTR
    
    FOR i&=1 TO 10
        S(i&)=STR$(100+i&)
    NEXT
    
    SPtr=VARPTR(S(3))
    ShowS3 BYVAL SPtr
END FUNCTION

Hope this helps,

Lasse Rantanen
[email protected]

[LRantanen]

A typo !!!

Instead of

FUNCTION ShowS3(x AS STRING PTR) AS LONGINCR x

of course there should be

FUNCTION ShowS3(x AS STRING PTR) AS LONG

Sorry,

Lasse Rantanen
[email protected]

[Joe Speroni]

Well Lasse, your code was not quite what I wanted, but I used
it to produce the following. I want to make an array of
string pointers (indexed by a COMBOBOX ID, and pointing to
the string array that have all the text for that COMBOBOX's
list. I greatly simplies the CallBack functions.

The code I got working follows. Thanks much for the samples
that got me working on the problem.
--------------------------------------------------------------
#COMPILE EXE
FUNCTION ShowS3(x() AS STRING) AS LONG
MSGBOX x(4)+"|"+str$(UBOUND(x))
END FUNCTION

FUNCTION PBMAIN() AS LONG
DIM S(1:10) AS STRING
FOR i&=1 TO 10:S(i&)=STR$(100+i&):NEXT
DIM SPtr AS STRING PTR:SPtr=VARPTR(S())
ShowS3 BYVAL SPtr
END FUNCTION


------------------

[Lance Edmonds]

You dont need to DIM a String Pointer just to get the addressm you can pass the address of the array directly to the function:

ShowS3 BYVAL VARPTR(s())

Of course, this is exactly the same as just passing the array, afterall!

ShowS3 s()

Joe, can you please use UUB codes when posting your source code...? Thanks!


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

[Joe Speroni]

Lance, I guess I was not clear (as usual) about why I was trying
to understand the syntax for handling string pointer parameters.
I understood how to pass an array as a parameter to a function,
in fact up at the top of this thread my first code submission
showed exactly that.

The problem I was trying to solve is how could a CALLBACK
function which has no parameters (other than CBCTL) access
the string array associated with the CONTROL ADD COMBOBOX
that created it. It can be done with a series of IF CBCTL=xxx,
ELSEIF CBCTL=yyy, ... , etc. But this is unwieldly and I was
looking for a way to just have an array of pointers indexed
by CBCTL to get to the array. I have around 50 COMBOXBOXES
and the code was getting out of hand!

I now "understand" the syntax to get this to work and I'd
recommend an example including such a usage.

The following code is a better example of what I was trying to
do (ShowS3 no longer has a parameter, like a CALLBACK function).

BTW I don't know what UBB stands for, but I searched the forum
and came up with your recommentation to put {code}, and
{/code} bracketing the code (where { and } are square brackets). I don't know
It is not clear why this is needed (get rid of spaces from
copy/paste operation?). I can access the code w/o them? But
I'll be sure to include them in the future. Does this address
the UBB code problem? Please clarify if I'm still not doing
it right.

And as always thanks to you and the many others who make this
forum so valuable! This forum should be a bigger part of
your advertising -- in addition to a great compiler.

Aloha,

Joe Speroni
-----------------------------------------------------------------

#COMPILE EXE
GLOBAL SPtr AS STRING PTR

FUNCTION GetElement(X() AS STRING,i AS LONG) AS STRING
FUNCTION=X(i):END FUNCTION

FUNCTION ShowS3() AS LONG
MSGBOX GetElement(BYVAL SPtr,3)
END FUNCTION

FUNCTION PBMAIN() AS LONG
DIM S(1:10) AS STRING:FOR i&=1 TO 10:S(i&)=STR$(100+i&):NEXT
DIM T(1:20) AS STRING:FOR i&=1 TO 20:T(i&)=STR$(200+i&):NEXT
DIM SPtr AS STRING PTR
SPtr=VARPTR(S())
ShowS3
SPtr=VARPTR(T())
ShowS3
END FUNCTION

------------------

[Lance Edmonds]

The UUB token pair [ CODE ] and [ /CODE ] tell the BBS software to preserve leading whitespace - this has the effect of preserving the code indenting so code is easier to read (with out the tokens, the BBS displays the text with leading whitespace stripped off).

Which of the following is easier to read?

for x& = 1 to 10
a = b + c + d + e
for y! = 1.1! to 2.1!
e = y! + z! + q!
if y! > 2! then exit for
next
a = b + c + d + e
next

for x& = 1 to 10
  a = b + c + d + e
  for y! = 1.1! to 2.1!
    e = y! + z! + q!
    if y! > 2! then exit for
  next 
  a = b + c + d + e
next

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

[Charles Dietz]

It seems to me that there are two different ways to pass an array
to a sub or function. Both ways actually pass an address but they
differ in how the address is taken.

Method 1: pass array by reference
Method 2: pass pointer to first element of array

   #COMPILE EXE
   #DIM ALL
   SUB ShowArray1(x() AS STRING, n AS INTEGER)
      MSGBOX x(n),, "Method 1"
   END SUB
   SUB ShowArray2(x AS STRING PTR, n AS INTEGER)
      MSGBOX @x[n - 1],, "Method 2"
   END SUB

   FUNCTION PBMAIN() AS LONG
      DIM S(1:10) AS STRING
      DIM SPtr AS STRING PTR
      LOCAL i AS INTEGER
      FOR i=1 TO 10
         S(i)=STR$(100+i) + " " + STRING$(i, "z")
      NEXT
      SPtr=VARPTR(S(1))
      ShowArray1 BYREF s(), 4      'method 1
      ShowArray2 BYVAL SPtr, 7     'method 2 
   END FUNCTION

------------------

[Lance Edmonds]

YOu are correct in that there are two ways to pass an array to a sub or function... the following information is found in the Inline Assembler chapter of the Help File:

Passing arrays

Each array in your program has an associated array descriptor. This descriptor is saved in a proprietary format, which may change from version to version of PowerBASIC. Since most of the information in the descriptor is not relevant to assembler code, it is usually best to simply pass a pointer to the first element of the array instead. You can use the VARPTR() function to retrieve that address. Subsequent elements of the array will immediately follow the first in memory, while multi-dimensional arrays are stored in column-major order.

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