Question about dynamic arrays

[Arnold]

Hi Charles,

may I ask for help? I refer to the demo \OxygenBasic\examples\WinGui\Toolbar1.o2bas in about line 147 and about line 187:

  ' bitmap for each button
  static tbBmp(7) as sys 'as BYTE
..
      for i = 0 to 6
..

I tried to replace 7 with a variable but this does not work. If I use a constant

  %count=7
  static tbBmp(count) as sys 'as BYTE
..
      for i = 0 to count-1

this will work and I see a difference if I change the value for count. So I tried:

int num=7
%count=num

this does fail. Is there a possibility to dimension arrays at runtime? I inspected Dynamic.inc but I do not know if I could use a function of this file? (I have not yet tried to test this)

Roland

[Charles Pegge]

Hi Roland,

Very briefly, this shows how to use a dynamic array:

Code: OxygenBasic

1. indexbase 0
2. sys i
3. sys be=256
4. byte b at getmemory be
5.  
6. for i=0 to be-1
7. 'access as b[i]
8. next
9. print i
10. ...
11. freememory @b
12.  

[Arnold]

Thanks Charles,

I now tried this:

Code: OxygenBasic

1. ...
2.  
3.   function WndProc(hWnd, wMsg, wParam,lparam) as sys callback
4.   ===========================================================
5.    
6.   static sys hdc, htools, hInstance
7.  
8.   static tbAddBmp as TBADDBITMAP
9.   static tbb      as TBBUTTON
10.   static iccx     as INITCOMMONCONTROLSEXtype
11.  
12. int num=7
13. sys ie=num
14.  
15.   '' bitmap for each button
16.  '  static tbBmp(7) as sys 'as BYTE
17. static int tbBmp at getmemory ie
18.  
19. ...
20.  
21.       '' apply bitmap to toolbar buttons
22.    '
23.      dim i,k as LONG
24.       for i = 0 to num-1
25.         if i=3 then k=TBSTYLE_SEP else k=TBSTYLE_BUTTON
26.         with tbb
27.         .iBitmap   = tbBmp(i)
28.         .fsState   = TBSTATE_ENABLED
29.         .fsStyle   = k
30.         .idCommand = -1
31.         .dwData    = 0
32.         end with
33.         SendMessage( hTools, TB_ADDBUTTONS, 1, @tbb)
34.       next
35.     end if
36. freememory @tbBmp
37.  
38.     case WM_DESTROY
39.     '===============
40. ...
41.  

Now everthing works as expected. If I did everthing correctly then the dynamic short-cut for dimensioning / allocating will be helpful in other situations too.


Roland

[Charles Pegge]

When allocating space for int arrays you will need to scale up by 4:

Code: OxygenBasic

1. static int tbBmp at getmemory ie*4 'sizeof int
2.  

[Arnold]

Hi Charles,

out of curiosity I tried this:

int num=7

  ' bitmap for each button
   static bstring tbBmp = news num*sizeof(int)
...
     '' apply bitmap to toolbar buttons
    '
      dim i,k as LONG
      for i = 0 to num-1
...

freememory @tbBmp

This seems to work and if it is correct I would have finally understood the meaning of bstring (block of bytes, allocated in memory which must be freed at some time).

Roland

[Charles Pegge]

Hi Roland,

Bstrings contain the string pointer, and should be freed using one of these: (without an address operator)

frees tbBmp

freememory tbBmp

[Arnold]

Hi Charles,

thanks again. You explained the usage of frees and freememory clearly in the Help file but I overlooked that the @ operator was omitted. I assume that I will free something different when I use freememory / frees with an address operator but not the block itself?

Is it correct that bstring means a block of bytes? I must admit that at least in the past few years I associated string only with "Text" and was astonished when I looked in a dictionary today and there were many translations and synonyms but text was not mentioned. Somehow this was my personel blackout. In the meantime I remember that in fact I learned something different in school.

Roland

[Charles Pegge]

Hi Roland,

Bstrings and Strings may contain any bytes including nulls, so they can be used for any binary data up to 2 gig in length.

Oxygen uses OleStrings/Bstr for all its dynamic memory allocations, in common with PowerBasic and thinBasic. (Under Linux it would have to be Malloc and Free).

When releasing dynamic objects and arrays, freememory requires the '@' or '&' operator, but not with individual bstrings. This is due to OxygenBasics implicit pointering.