Argument can`t be assigned to
lazarus / 64-FPC development

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nitinjain · 2014-05-15 12:45

Hi,

I am trying to implimenting the below code but there are showing error
that is : "Argument can`t be assigned to ".

**Implimenting Code
-------------------------------------------------------
type Pbyte = ^Byte, Pword = ^Word, Pdword = ^LongWord;

function GetMem( addr: LongWord ) : Byte;
begin
var ptr : PByte;
ptr := PByte(addr)
GetMem := ptr^
end;

procedure SetMem( addr: LongWord; value: Byte );
begin
var ptr: PByte;
ptr := PWord(addr);
ptr^ := value
end;
-----------------------------------------------------

**And My code is shown below, where i want to implement the above
code.
--------------------------------
BEGIN
MEMW[$B800:(width_offset-1)*2
+(height_offset-1)*160]:=current_locatio...
current_location:=current_location^.next...
END;
-----------------------------------
BEGIN
offset:=(top_left_x-1)*2
+(top_left_y-1)*160;
MEM[$B800:offset]:=top_left_corner[style...
MEM[$B800:offset+1]:=back*16+fore;
---------------------------------------...

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marcov · 2014-05-15 13:43

That code

1) doesn't compile, and fails basic syntax checks on several places.
2) will never be any use in implementing the bottom code anyway, since
the textmode screen is not memory mapped in linear addres space in any
modern system. (and even in Dos, there it is in the first MB)

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nitinjain · 2014-05-15 14:11

Yes, I agreed and i have fixed those basic errors and after that I got
this error "Argument can`t be assigned to" on both places (at MEM and
MEMW starting point)

**Implimanting Code after changed
----------------------------------------------------
TYPE Pbyte = ^Byte; Pword = ^Word; Pdword = ^LongWord;

FUNCTION GetMem( addr: LongWord ) : Byte;
var ptr : Pbyte;
BEGIN
        addr :=$B800;
   ptr := PByte(addr);
   GetMem := ptr^;
END;

PROCEDURE SetMem( addr: LongWord; value: Byte );
var ptr: Pbyte;
BEGIN
        addr :=$B800;
   ptr := Pbyte(addr);
   ptr^ := value;
END;

FUNCTION GetMemW( addr: LongWord ) : Word;
var ptr : Pword;
BEGIN
        addr :=$B800;
   ptr := Pword(addr);
   GetMemW := ptr^;
END;

PROCEDURE SetMemW( addr: LongWord; value: Word );
var ptr: Pword;
BEGIN
        addr :=$B800;
   ptr := Pword(addr);
   ptr^ := value;
END;
------------------------------------------

2) actually this code used for formating. If I commented this code (as
you said), my messages box borders and colors not appeared.

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typo · 2014-05-15 14:25

http://www.freepascal.org/docs-html/user/userse63.html

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nitinjain · 2014-05-15 14:29

could you please guide me what and where I need to change in my code.

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typo · 2014-05-15 14:36

In fact I can compile your code with no error messages, but with these
hints:

Code: [Select]type Pbyte = ^Byte;
     Pword = ^Word;
     Pdword = ^LongWord; // Hint: Local type "Pdword" is not used

FUNCTION GetMem( addr: LongWord ) : Byte;
var
  ptr : Pbyte;
BEGIN
  addr :=$B800;
  ptr := PByte(addr);  // <<<<< Hint: Conversion between ordinals and
pointers is not portable
  GetMem := ptr^;
END;

PROCEDURE SetMem( addr: LongWord; value: Byte );
var
  ptr: Pbyte;
BEGIN
  addr :=$B800;
  ptr := Pbyte(addr);  // <<<<< Hint: Conversion between ordinals and
pointers is not portable
  ptr^ := value;
END;

FUNCTION GetMemW( addr: LongWord ) : Word;
var
  ptr : Pword;
BEGIN
  addr :=$B800;
  ptr := Pword(addr); // <<<<< Hint: Conversion between ordinals and
pointers is not portable
  GetMemW := ptr^;
END;

PROCEDURE SetMemW( addr: LongWord; value: Word );
var
  ptr: Pword;
BEGIN
  addr :=$B800;
  ptr := Pword(addr);  // <<<<< Hint: Conversion between ordinals and
pointers is not portable
  ptr^ := value;
END;

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marcov · 2014-05-15 14:37

Quote from: nitinjain on May 15, 2014, 04:11:02 pmYes, I agreed and i
have fixed those basic errors and after that I got this error
"Argument can`t be assigned to" on both places (at MEM and MEMW
starting point)

See point (2).   memw is never going to work on something else than
dos.
 
The whole "screen is at $B800" concept is a DOSism.