[Lazarus] Use of Move()?

[Bo Berglund]

On Tue, 01 Feb 2011 23:33:58 +0100, Marc Weustink
<marc at dommelstein.net> wrote:

>
>Just tested:
>
>program MoveTest;
>{$mode objfpc}{$H+}
>uses
>   SysUtils;
>var
>   S: String;
>   I: Integer;
>   P: Pointer;
>begin
>   S := 'Bla';
>   S := S + S;
>   P := @I;
>   Move(S[1], P^, SizeOf(I));
>
>   WriteLn(Format('%x %x %x %x %8.8x', [Ord(S[1]), Ord(S[2]), Ord(S[3]), 
>Ord(S[4]), i]));
>end.
>
>$ ./movetest
>42 6C 61 42 42616C42
>

My code is a bit more complex because I want to be able to read and
write different types of variables to the buffer handler.
As an example I have the case of a string variable. To write it into
the buffer I use this overloaded write:

function TSSCommBuf.Write(const Source: string): boolean;
begin
  Result := Write(@Source[1], Length(Source));
end;

and for a Cardinal argument I use this:

function TSSCommBuf.Write(const Source: Cardinal): boolean;
begin
  Result := Write(@Source, SizeOf(Source));
end;

both of which then calls the main Write:

function TSSCommBuf.Write(Source: Pointer; Count: Cardinal): boolean;
var
  b: byte; //For debugging, will be removed later
  Dst: Pointer; //Suggestion from Marc Weustink
begin
  Result := false;
  //Check buffer size and grow if needed
  if (FBufSize - FWriteIndex) < Count then
    ExpandBuffer(FWriteIndex - FBufSize + Count);
  Dst := @FBuf[FWriteIndex];
  Move(Source, Dst^, Count); // Source and Dst are pointers
  b := FBuf[FWriteIndex]; //To check what actually was written
  FWriteIndex := FWriteIndex + Count;
  Result := true;
end;

When I call the Write method with a string argument I get first to the
small overloaded function, which unifies the arguments and calls the
main Write.

But when I test this with the string containing the single char #6
then the value that actually gets written is #64....

So somehow I am missing something important here...


Bo Berglund