Absolute Types

[Dave Stanton]

I'm trying to use types to extract information at fixed locations
in memory.
For example to modify the PBVUSERAREA.
I can do it this way.

     TYPE PBVUSERTYPE
          Check AS BYTE
          Action AS BYTE
          Level AS BYTE
          Retval AS BYTE
          Caller AS STRING * 12
          Spare AS STRING * 16
     END TYPE

     DIM Pu AS PBVUSERTYPE
     Q$=PBVUSERAREA
     LSET Pu=Q$
     Pu.Caller="MYPROG.BAS"
     PBVUSERAREA=Pu

I thought it may be easier to DIM the type at an absolute address

     DIM ABSOLUTE Pu AS PBVUSERTYPE AT VARPTR32(PBVUSERAREA)/16

but the compiler complained.

Is my syntax wrong, or it just can't be done.

Any comments appreciated.

Dave

<[email protected]>

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[This message has been edited by Dave Stanton (edited October 26, 2000).]

[Lance Edmonds]

Sorry, but there is no native way to get a pointer to the pbvUserArea internal variable... you'll have to stick with the conventional assignment method.

Of course, if you copy the data in pbvUserArea to your UDT, you can use a pointer to the UDT... just not to pbvUserArea itself.


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

[Dave Stanton]

Thanks Lance, you'r still awake, no rest for the wicked.
Dave.


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[Lance Edmonds]

Dave, it's only 10:45pm in New Zealand (I telecommute to work!). NZ is almost a whole day ahead of the US (Pacific time), because NZ is at GMT+12:00.

Living in NZ does have benefits... we see the new year in before the rest of the world!



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

[Dave Stanton]

I know, I'm in the Emerald City (Sydney).
I take your point about the PBVUSERAREA, but how would I go
using a TYPE over the BIOS area, for example.

TYPE Kbdbuftype
     Unused   AS STRING * 10
     Nextchar AS WORD
     Lastchar AS WORD
     Kbdbuf   AS STRING * 16   
END TYPE

Using  

   DIM ABSOLUTE Kb AS Kbdbuftype AT &H41

doesn't want to compile.

Any thoughts?

Dave

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[This message has been edited by Dave Stanton (edited October 26, 2000).]

[Michael Mattias]

You can DIM ABSOLUTE a single UDT by making a one-element array:

DIM foo (0) AS whatever AT whereever

Then you can move the data using a pointer to element 0.

But why bother? Just use a dataname as UdtType PTR

(But why you are dividing VARPTR32 by 16 is a mystery to me)

MCM

[Dave Stanton]

MCM
I'm probably wrong, but I understood that DIM AT required a segment
address; VARPTR returns the full Segment : offset.
Seg=VARPTR\16 reduces the offset to usually <16.
Thanks for your pointers (sorry)

Dave



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[This message has been edited by Dave Stanton (edited October 27, 2000).]

[Michael Mattias]

Duh. I forgot that in PB/DOS, you DIM AT "segment" rather than as in PB/Win, where you DIM AT "absoluteaddress."

It's just that I never used divide by 16 to get the segment from a VARPTR32.

Under DOS, the segment is just VARSEG (variable).

MCM

[Dave Stanton]

Michael,
Actually, I was wrong.
For a segment with the minimum offset, I should have used.

     Xseg???= VARSEG(PBVUSERAREA)+VARPTR(PBVUSERAREA)\16

but as arrays always start at an offset of 0 in a sement

    DIM ABSOLUTE Pu(0) AS PBVUSERTYPE AT VARSEG(PBVUSERAREA)

works well.
Thanks.

Dave



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[Lance Edmonds]

Hmmm... I stand corrected... I have always believed it was not possible to get access to the pbvUserArea block that way.

Cute solution!


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

[Michael Mattias]

Isn't it easier to just...

DIM Udt AS UdtType
DIM UDTPtr AS UdtType PTR
UDTPtr = VARPTR32(pbvUserArea)
UDT= @UdtPtr

MCM

[Dave Stanton]

Magic Michael,
Thank you
Dave

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