Pointer lesson 2 needed I think :)

[Mike Doty]

TYPE TEST
   TX AS LONG       ' member 'tx' is a pointer variable  (removed pointer)
END TYPE
 
FUNCTION PBMAIN () AS LONG
  LOCAL t1$, blk AS test
  LOCAL  K AS ASCIIZ PTR                 'changed from STRING PTR
  t1$="pointers-grr pointers" + CHR$(0)  'or use ASCIIZ strings
  blk.tx = STRPTR(t1$)
  blk.tx = blk.tx + 9
  K = blk.tx : ? @K
END FUNCTION

TYPE TEST
   TX AS LONG
END TYPE
 
FUNCTION PBMAIN () AS LONG
  LOCAL t1 AS ASCIIZ * 128
  LOCAL blk AS test
  LOCAL k AS ASCIIZ PTR
  t1="pointers-grr pointers"
  k = VARPTR(t1) + 9
  ? @k
END FUNCTION

FUNCTION PBMAIN () AS LONG
  LOCAL t1 AS STRING
  LOCAL x AS LONG
  LOCAL Address AS DWORD
  t1="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  Address = STRPTR(t1)
  FOR X = 1 TO LEN(t1)
   ? CHR$(PEEK(Address+x-1));
  NEXT
  ?
  LOCAL count AS LONG
  count = 1
  FOR X = 1 TO LEN(t1)
    ? PEEK$(address + x-1, count&);
  NEXT
  ?
  ? PEEK$(address,LEN(t1))
  WAITKEY$
END FUNCTION

[Michael Mattias]

If you want substrings, use the provided substring functions, don't increment pointers like that...

 LOCAL S  AS AS STRING, T AS STRING
 LOCAL ps AS STRING PTR 
  S   = "Hello World"
  pS = VARPTR (s) 
  T   = MID$(@ps, 7,5) 
  MSGBOX T

MCM

[Adrian Verkuil]

Yes , one thing MM

IF you use the pointer like I did :

blk.tx = blk.tx + 9

K = varptr(blk.tx)

msgbox @K

Then the string comes out ok in MSGBOX so offset 9 plus, but when you try this:

[email protected] then it fails, would it not be nice it gives back a new substring Then?

[Michael Mattias]

>Is this correct ..?

Does it work as you intended? Then it's correct.

[Adrian Verkuil]

MM This what I needed,

Use a member of a struct as pointer to a string.
Is this correct Michael?

#COMPILE EXE
#DIM ALL

TYPE TEST
   TX AS long ptr      ' member 'tx' is a pointer variable
END TYPE 

FUNCTION PBMAIN () AS LONG
LOCAL t1$, blk AS test    
LOCAL  K as string ptr

t1$="pointers-grr pointers"
 
blk.tx = strptr(t1$)

blk.tx = blk.tx + 9

K = varptr(blk.tx) : msgbox @K  

END FUNCTION

Output grr pointers

[Adrian Verkuil]

MM Thanks ,

These 2 below grrrr.. cost me e a few hours !
Now I see it I understand. but that is mostly the case.

@blk.TX and [email protected]

[Michael Mattias]

The "@" must immediately precede the name of a pointer variable:

TYPE TEST
   TX  AS string PTR    ' member 'tx' is a pointer variable
END TYPE 

FUNCTION PBMAIN () AS LONG
LOCAL t1$,_
   blk AS test    ' blk is NOT a pointer variable, it is a 'test' 

 @blk.TX  <<< invalid, "blk" is not a pointer variable
  [email protected]   <<< valid, "tx" member of blk IS defined as pointer variable

[Adrian Verkuil]

I think I mix up a a few things in my mind for sure

#COMPILE EXE
#DIM ALL

TYPE TEST
   TX  AS string PTR
END TYPE 


FUNCTION PBMAIN () AS LONG
LOCAL t1$, blk AS test

t1$="TEST"

blk.TX = strptr(t1$)
msgbox @blk.TX 

' both give pointer var error ??
 
blk.TX = varptr(t1$)
msgbox @blk.TX        

     

END FUNCTION